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Soil water characteristic curve (SWCC) can show the soil water holding capacity, and is the relationship between the soil matric potential and saturation. The expansive soil has the characteristics of strong swell-shrink, developing fissures and over consolidation, especially under drying-wetting cycles. Its water holding capacity, which has an important impact on the soil properties, is totally different from the capacity of full soil. Therefore, how to exactly obtain the matric suction of expansive soil under drying-wetting cycles is very important to analyze the characteristics of mechanics and deformation of expansive soil. In order to analyze the change rule of matric suction of expansive soil under drying-wetting cycles, the artificial rainfall and evaporation was applied in drying-wetting tests of expansive soil. The specimens sized at 102 mm × 40 mm (diameter × height) were made by compaction apparatus and the initial dry density was 1.68 g/cm3. All the specimens were saturated after compaction and undergoing drying-wetting cycles in constant temperature (22 ℃) environment. The small electric fans were adopted to increase the rate of evaporation until the mass of specimens was kept constant under the condition of drying. Then the water vapours were sprayed to the surface of specimens by humidifiers until the process of infiltration stopped under the condition of wetting. That is one drying-wetting cycle so far. In this paper, 4 set of experiments under drying-wetting cycles were carried out and the cycle times were 1, 2, 3 and 4 respectively. Then 11 specimens sampled by cutting rings (61.8 mm × 20 mm (diameter × height)) in different volumetric water content were obtained in each process of drying and wetting respectively. The matric suction of each specimen was measured with filter paper of Whatman No. 42 and then the SWCCs were obtained under drying-wetting cycles. The corresponding air-entry values and residual values in different drying-wetting cycle times were calculated from SWCC. Ulteriorly, the different SWCCs obtained in different drying-wetting cycle times were fitted by the Fredlund SWCC model. Based on the above analysis, an SWCC model of expansive soil considering drying-wetting cycle effect was established finally. The results showed that: 1) With the increase of drying-wetting cycle time, the air-entry value of expansive soil was evidently reduced. Compared with the air-entry value (134.5 kPa) of expansive soil undergoing one drying-wetting cycle, the air-entry value was 58.5 kPa and reduced by 56.5% undergoing 4 drying-wetting cycles. The most effect of drying-wetting cycles on air-entry value occurred in the first cycle. 2) With the increase of drying-wetting cycle time, the residual value of expansive soil was also reduced. Compared with the residual value (1040.5 kPa) of expansive soil undergoing one drying-wetting cycle, the residual value was 528.5 kPa and reduced by 49.2% undergoing 4 drying-wetting cycles. Moreover, the residual value is reduced evidently after undergoing one drying-wetting cycle and it cannot yet be stabilized with the increase of drying-wetting cycle time. That means the effect of drying-wetting cycles on ari-entry value is much greater than on residual value. 3) The fitted parameters in the SWCC model of expansive soil considering the effect of drying-wetting cycle have a good linear correlation with the drying-wetting cycle time. With the increase of drying-wetting cycle time, the soil air-entry value and change rate of water content reduce while the residual value increases gradually. The results can provide a reference for the further analysis on soil matric suction and its application in engineering. [ABSTRACT FROM AUTHOR]

Purple soil is widely distributed in southwestern China and is one of the important natural resources. Because of the loose parent rock and low degree of differentiation, purple soil is characterized by a loose structure that is easily eroded and high soil fertility. Soil erosion is very serious in the purple soil region, which is one of the main sources of sediment in the upper reaches of the Yangtze River, and has a certain impact on the agricultural production and engineering development in the purple soil region. After erosion, purple soil shows the characteristics of reduced dry density of soil and serious loss of fine particles, which affects its water-holding characteristics. In order to explore the changes of soil water-holding properties of purple soil after rainfall erosion, this study was carried out to analyze the effect of missing grain groups on the water-holding properties of sandy clayey purple soil under rainfall conditions by selecting three test methods, namely, axial translation technique, filter paper method, and saturated salt saturated saline solution vapor equilibrium technique for the three grain groups which are the most susceptible to changes in the rainfall conditions, and carrying out the Soil-Water Characteristic Curve (SWCC) test with the absence of grain groups within the full suction range to analyze the effect of the missing grain groups on the water-holding properties of sandy clayey purple soil. The results show that: 1) the missing grain group reduces the water-holding characteristics of sandy clayey purple soil, which is most obvious in the boundary effect zone and transition zone, and has less effect on the residual zone. The mass of the missing grain group is inversely proportional to the air intake value and the residual water content. 2) Using the grain size parameters (Constrained diameter、Average diameter、Median diameter、Effective diameter) to characterize the soil grading condition, the relationship between the soil grading curves and the characteristic values of SWCC was established. It was found that except for effective diameter, the other parameters were linearly inversely related to the air intake value and residual water content; 3) The data obtained from different methods were fitted using the Fredlund-Xing model, and it was found that the results of the data obtained from a single test method fitted better, but the SWCC significantly deviated from the test data points in the boundary effect zone and the transition zone. Root mean square error (RMSE)、 percent bias (PB) and mean absolute percent relative error (MAPRE) were introduced as evaluation indexes, and it was found that the suction range was the main factor affecting the fitting effect of SWCC, and within a certain suction range, the larger the range of data points involved, the better the model fitting effect was, and after a certain suction value was reached, the suction range had very little effect on the model fitting effect. It is proposed that to obtain the accurate SWCC of purple soil quickly, only the maximum suction value needs to be determined, and the number of test points with high suction is reduced, which can effectively shorten the SWCC test period. The results lay a foundation for the subsequent study of the role of soil erosion and water-holding characteristics of purple soil, and also provide reliable ideas for the prevention of soil erosion and the application of soil-water characteristic curves in the Three Gorges Reservoir area. [ABSTRACT FROM AUTHOR]

Grapevine in seasonally frozen regions needs to be warm-insulated by soil in winter with the antifreezing soil removed in spring most mechanically by a soil removal machine. The purpose of this paper is to simulate the interaction between the insulating soil (with sandy loam texture) and the soil-cleaning materials (Q235 steel, rubber) commonly used in the soil removal machine, based on the discrete element method. The simulation model was constructed based on properties of the soil by integrating the hysteretic spring contact model (HSCM) and the linear cohesion model (LCM) as the contact model between soil particles. We took soil-soil restitution coefficient, soil-soil frictional coefficient, soil-soil rolling coefficient and soil cohesion energy density as the determinants and the soil accumulation angle as an evaluation index. The 4-factor universal rotation center combination simulation test, based on the EDEM, was used to regress the relationship between the determinants and the index using the Design-Expert software. The results showed that the soil-soil frictional coefficient was the only parameter that did not have significant effects on the soil accumulation angle. The best contact-parameter combination between soil particles was obtained by taking the physically measured soil accumulation angle as the optimization objective, which gave 0.51 for the soil-soil restitution coefficient, 0.65 for the soil-soil frictional coefficient, 0.06 for the soil-soil rolling frictional coefficient, and 10 495 J/m³ for the soil cohesion energy density. The associated soil accumulation angle was 31.74°, with a relative error of 0.83% compared with the physically measured results. The universal testing machine for soil yield test was used to obtain the HSCM model parameters based on the change in penetration stress with the displacement, and the resultant soil yield strength was 0.38 MPa. The static frictional coefficient between soil and Q235 steel as well as the rubber measured by the inclination test bench was 0.38 and 0.48 respectively. These data and the EDEM were used to conduct the simulation test of the soil slip, with the restitution coefficient and the rolling frictional coefficient between soil and the materials taken as the determinants and the sliding frictional angle as evaluating index. Regressing the test date with the two-factor universal rotation center combination test showed that the rolling frictional coefficient between soil and the materials had a significant effect on the sliding frictional angle between soil and the steel plate and rubber. In contrast, the restitution coefficient between the soil and the materials impacted significantly on the sliding frictional angle between the soil and the rubber but not on the soil and the steel plate. The restitution coefficient and the rolling frictional coefficient between the soil and the Q235 steel as well as the rubber were optimized by using the measured sliding frictional angle as the optimization objective. The resultant restitution coefficient and the rolling frictional coefficient were 0.60 and 0.37 respectively for the soil and the Q235 steel, and 0.61 and 0.23 respectively for the soil and the rubber. Soil bin test and simulation test of the scraper were conducted to verify the calibrated discrete element model parameters. The horizontal forward resistance of the scraper in the soil bin test and simulation test was 228.36 and 213.79 N respectively, with a relative error of 6.38%. The results presented in this paper have important implications for using discrete element method to analyze the removal of grapevine-insulating soil. [ABSTRACT FROM AUTHOR]

Purple soil which riches in mineral nutrients and is the main farming soil in Southwest China. Purple soil color images collected by machine vision have complex background, including crops, weeds, scattered small soil blocks and surface soil because of its stochastic field scenes. In order to avoid the interference of background on further processing and recognition of purple soil with machine vision, it is a primary task to segment the purple subsoil region from its background adaptively. Clustering algorithm has achieved good results in image segmentation and is widely applied. However, the selection of parameters of some classical clustering algorithms are sensitive, which need to be manually set and cannot satisfy to the adaptive segmentation of purple soil. Thus, aiming at the problem of adaptive segmentation, a segmentation methool of purple soil color image based on adaptive density peaks clustering was proposed in this paper. The specific segmentation algorithm was as follows: firstly, in order to calculate the density peaks conveniently and increase the separability between soil region and its background, a color to gray transformation method was carried out. The entropy-based similarity matrix was constructed, then the optimization model based on maximizing the between-class variance and minimizing the withinclass variance criterion was established with the similarity matrix. The optimization model was solved to obtain the gray matrix, which enhanced the separability of the gray value for clustering. Secondly, in the light of the shortcomings of density peaks algorithm, the density formula was improved and a measure was designed to determine the clustering centers adaptively, which realized the adaptive segmentation of purple soil region with the clustering algorithm based on the density peaks clustering framework, and improved the initial segmentation accuracy. Finally, post-processing algorithms of boundary extraction and region filling were designed to remove both the discrete small soil blocks in the background area and the internal voids in the soil area of the image obtained by initial segmentation. Therefore, the purple soil region image could be completely obtained and the segmentation accuracy of soil region was improved. From purple soil color images collected by machine vision in the field, 60 images with normal illumination, no surface soil and no shadows around the subsoil were randomly selected as normal test images and divided into 20 groups.we picked out randomly 60 images with the characteristics of normal illumination, then another 60 images were randomly selected as robustness test images, which were characterized by scattered subsoil and some shadows around the topsoil. These images were divided into 20 groups. The results of contrast test showed that the proposed method could automatically segment the purple soil color images of normal test and robustness test. For 60 normal test images, average segmentation accuracy of the proposed algorithm were 93.45%, which were 11.54, 7.96, 3.16 and 0.85 percentage points higher than that of FRFCM (fast and robust fuzzy C-Means) algorithm, H-threshold algorithm, DPC (density peaks clustering) algorithm and DFDPC (data field based density peaks clustering) algorithm, respectively. For 60 robustness test images, average segmentation accuracy of the proposed algorithm were 87.40%, which were 11.75, 5.2, 12.47 and 3.09 percentage points higher than that of FRFCM algorithm, H-threshold algorithm, DPC algorithm and DFDPC algorithm, respectively. The results proved that the proposed algorithm in this paper was superior to the other four comparison algorithms. Furthermore, boundary extraction algorithm and region filling algorithm further improved the average segmentation accuracy of soil region, in the post-processing stage. In the final exact segmentation results, average segmentation accuracy of normal test images were 96.30%, with average time-consuming of 0.36 s，and average segmentation accuracy of robustness test images was 91.63%, with average time-consuming of 0.35 s. In conclusion, the proposed algorithm was effective, and it can provide reference for the segmentation and extraction of purple soil region from the computer vision image. [ABSTRACT FROM AUTHOR]

Accurate and effective drought monitoring using remote sensing technology is essential for regional and global drought warning and forecasting. Especially, soil moisture (SM) is one of the key potential factors affecting agricultural drought. At present, most studies ignore the fact that soil moisture is a complex nonlinear coupling system，the research only using visible light, near infrared, short-wave infrared, thermal infrared and other remote sensing drought index has certain limitations in SM inversion. A new method of retrieving farmland SM of winter wheat at returning green stage based on MODIS and radial basis function neural network (RBFNN) is presented in this paper. Firstly, the adaptability of various MODIS-derived drought indices is analyzed in the period of seedling establishment of winter wheat, including soil water content, crop morphological change in water requirement, crop canopy water content and temperature and other parameters. Secondly, the correlation between the original remote sensing drought indices and the soil relative humidity 10 cm soil layer was analyzed. A comprehensive evaluation set of apparent thermal inertia (ATI), vegetation supply water index (VSWI), enhanced vegetation index (EVI), normalized difference infrared index band7 (NDIIB7), normalized multi-band drought index (NMDI) and temperature condition index (TCI) are selected to invert soil moisture of farmland. Finally, combining MODIS remote sensing drought index with RBFNN, the SM of farmland was retrieved synergistically, and the retrieved results were compared with those of BP-NN and linear regression (LR) models. The experimental study is conducted in Henan province of China, MODIS reflectance products (MOD09A1) and temperature products (MOD11A2) at returning green stage of winter wheat from 2001 to 2012 were used to extract remote sensing drought indices, and the global land cover product of MODIS (MCD12Q1) is selected to obtain cropland distributions. Soil moisture data is derived from the “China crop growth and development and farmland soil moisture ten-day dataset”, which contains the soil relative humidity of 10 and 20 cm soil layer observed every 10 days by 17 soil moisture stations. The results show that the average accuracy of SM inversion model using RBFNN and multiple drought indices is 93.27%, which is increased by 2.92 and 9.97 percentage points compared with BP-NN and LR model, respectively. Most of the data points of the three models are concentrated around the 1:1 line, which indicate that there is a good correlation between the predicted value and the measured value. Compared with BP-NN model and LR model, the deviation between predicted value of RBFNN model and the 1:1 line is the smallest, the higher the regression correlation coefficient is, the higher the determination coefficient is. SM is significantly correlated with ATI, NDIIB7 and VSWI in the early growth stage of winter wheat. Multi-band remote sensing drought monitoring indices can comprehensively reflect the changes of crop physiology and morphology under soil water stress, and also determine the retrieval accuracy of the humidity model simultaneously. In this paper, only winter wheat in returning green stage is selected as the research object, and the comprehensive evaluation index set selected is not suitable for SM inversion of other growth stages of winter wheat, the adaptability of different remote sensing drought indices in different growth stages needs further experimental study. The study provides a new case for regional SM inversion from remote sensing-based drought monitoring indices and neural network. [ABSTRACT FROM AUTHOR]

Accurate and effective drought monitoring using remote sensing technology is essential for regional and global drought warning and forecasting. Especially, soil moisture (SM) is one of the key potential factors affecting agricultural drought. At present, most studies ignore the fact that soil moisture is a complex nonlinear coupling system，the research only using visible light, near infrared, short-wave infrared, thermal infrared and other remote sensing drought index has certain limitations in SM inversion. A new method of retrieving farmland SM of winter wheat at returning green stage based on MODIS and radial basis function neural network (RBFNN) is presented in this paper. Firstly, the adaptability of various MODIS-derived drought indices is analyzed in the period of seedling establishment of winter wheat, including soil water content, crop morphological change in water requirement, crop canopy water content and temperature and other parameters. Secondly, the correlation between the original remote sensing drought indices and the soil relative humidity 10 cm soil layer was analyzed. A comprehensive evaluation set of apparent thermal inertia (ATI), vegetation supply water index (VSWI), enhanced vegetation index (EVI), normalized difference infrared index band7 (NDIIB7), normalized multi-band drought index (NMDI) and temperature condition index (TCI) are selected to invert soil moisture of farmland. Finally, combining MODIS remote sensing drought index with RBFNN, the SM of farmland was retrieved synergistically, and the retrieved results were compared with those of BP-NN and linear regression (LR) models. The experimental study is conducted in Henan province of China, MODIS reflectance products (MOD09A1) and temperature products (MOD11A2) at returning green stage of winter wheat from 2001 to 2012 were used to extract remote sensing drought indices, and the global land cover product of MODIS (MCD12Q1) is selected to obtain cropland distributions. Soil moisture data is derived from the “China crop growth and development and farmland soil moisture ten-day dataset”, which contains the soil relative humidity of 10 and 20 cm soil layer observed every 10 days by 17 soil moisture stations. The results show that the average accuracy of SM inversion model using RBFNN and multiple drought indices is 93.27%, which is increased by 2.92 and 9.97 percentage points compared with BP-NN and LR model, respectively. Most of the data points of the three models are concentrated around the 1:1 line, which indicate that there is a good correlation between the predicted value and the measured value. Compared with BP-NN model and LR model, the deviation between predicted value of RBFNN model and the 1:1 line is the smallest, the higher the regression correlation coefficient is, the higher the determination coefficient is. SM is significantly correlated with ATI, NDIIB7 and VSWI in the early growth stage of winter wheat. Multi-band remote sensing drought monitoring indices can comprehensively reflect the changes of crop physiology and morphology under soil water stress, and also determine the retrieval accuracy of the humidity model simultaneously. In this paper, only winter wheat in returning green stage is selected as the research object, and the comprehensive evaluation index set selected is not suitable for SM inversion of other growth stages of winter wheat, the adaptability of different remote sensing drought indices in different growth stages needs further experimental study. The study provides a new case for regional SM inversion from remote sensing-based drought monitoring indices and neural network. [ABSTRACT FROM AUTHOR]

The purpose of the study was to improve the pertinence and accuracy of salinization monitoring and control. The main data sources for this paper include agricultural land classification database, 1:500 000 spatial distribution data of saline-alkali land, China earth international exchange station climate data daily value sata set (V3.0), 1:1 000 000 soil database data, 1:1 000 000 spatial distribution data of soil texture in China, land change survey database and other data of Heilongjiang Province. With the support of the above data, on the one hand, research starts from the connotation of land salinization, filtered out land risk assessment factor from numerous factors, include landform, soil texture, evaporation and precipitation ratio, groundwater mineralization, regional sensitivity, land use level, the relationship between land salinization and its correlation was analyzed by the grey correlation model, and used the grey correlation model to analyze the correlation between these factors and land salinization, in order to verify the rationality of the selection of indicators, based on this, carry out grid training and accuracy test, formed land salinization assessment model. On the one hand, started from the extension of land salinization, screened out the resistance factors of soil salinization diffusion or migration, and constructed a resistance surface, used the minimal cumulative resistance model to evaluate the risk pattern of land salinization landscape. After the above work was completed, then with the help of ArcGIS spatial analysis function, superimposed the evaluation results of land salinization danger and land salinization landscape risk pattern, Formed land salinization type zones and monitoring levels. This paper takes Heilongjiang Province as an example to apply the method, the main research results were summarized as follows: 1) In terms of the salinity danger of the land, the land salinization danger of the salinity risk of severe and above land were mainly distributed in the southwestern part of the Songnen Plain, moderately distributed in the north-central part of the Songnen Plain and the northeastern part of the Sanjiang Plain. The light and below were mainly distributed in the great and small xing'an ridge and the southeastern mountainous areas. Eastern Songnen Plain and Southern Sanjiang Plain. 2) In terms of risk pattern, the severe and above were not only distributed in the central and northern parts of the Songnen Plain, but also in the central and northern parts of the Songnen Plain. In addition, there were also a small distribution in the northeastern and southeastern mountain areas of the Sanjiang Plain; moderately except in the Songnen Plain. The northern part and the northeastern part of the Sanjiang Plain were distributed, in the Middle and Central South of the Songnen Plain, the central and western parts of the Sanjiang Plain, and the southeastern mountain areas were also distributed; the mild and the following risk patterns were mainly distributed in the great and Small Xing’an Ridge, in addition to Sanjiang there is a small distribution on the southern edge of the plains and southeastern mountains. 3) The monitoring level of salinization in Heilongjiang Province showed the overall pattern of the west > east > central, northern and southern regions, the high-level and medium-level monitoring areas were mainly distributed in the western, southwestern, northern parts of the Songnen Plain, and the northeastern part of the Sanjiang Plain, the low-level monitoring areas were mainly distributed in the eastern part of the Songnen Plain, in the south of the Sanjiang Plain, and in the southeastern mountain areas, non-monitoring areas were mainly distributed in the large and Small Xing'an Mountains. The conclusion is that the land salinization monitoring area identification technology based on the risk and landscape ecological risk pattern takes into account the connotation of salinization and the extension of salinization, which provides scientific basis for the monitoring and prevention of land salinization. [ABSTRACT FROM AUTHOR]

In this paper, a soil pore segmentation method based on fully convolutional network (FCN) is proposed to improve the accuracy of pore segmentation in soil image and provide technical support for the research of soil science. Taking the soil of typical black soil as the research object, the soil computed tomography image were obtained by scanning and cutting. Based on the FCN network, the soil image and the calibrated image of pore structure were input for convoluting, pooling and deconvoluting operations, and the error between the prediction image and the calibration image was used as feedback to complete the forward inference operation. Then, the weight value was updated by the back propagation algorithm to establish the soil pore segmentation model. Fully considering the pore geometry and spatial distribution characteristics, the pore model can accurately output the soil pore binary image. Meanwhile, the commonly used segmentation methods in the literature, such as Otsu method, watershed method, regional growth method and Fuzzy C-means method (FCM) were adopted for the comparative experiments on soil computed tomography images with low pore density (0-0.03), medium pore density (0.03-0.1) and high pore density (0.1-1) which were defined by porosity of soil. The experimental results showed that the watershed method and the regional growth method overestimate the pore structure of different geometries, including cracks between the pores, whereas the Otsu method and FCM method tended to overestimate the macropores and underestimate the micropores. Compared the five methods, the FCN method can accurately extract the pore structures with vary topologies from the complex soil computed tomography images with low, medium and high pore density. Moreover, the segmentation accuracy rate, over-segmentation rate, and under-segmentation rate were used to evaluate the soil pore segmentation performance of five methods. Based on 1487 soil computed tomography images, the average segmentation accuracy of FCN pore segmentation method was 98.1%, which was 25.6%, 48.3%, 55.7% and 9.5% higher than that of Otsu method, watershed method, regional growth method and FCM method. The average over-segmentation rate of the FCN pore segmentation method was 2.2%, which was only 33.8% of the suboptimal method (FCM method), respectively. And the average under-segmentation rate of the FCN pore segmentation method was 1.3%, which was only 23.6% of the suboptimal method (FCM method). In total, the FCN method can accurately extract the pore topology, restore the spatial distribution of pores and its application can make up for the shortcoming that the traditional segmentation method only uses the low-level features (gray and edge) when extracting the pore structure. Owing to the multiple convolution layers in the network, the FCN method can obtain the vary features of pore structure, so it has strong generalization ability and robustness of pore segmentation for different types of soil images. This paper will has a good reference for the microscopic process simulation , 3D reconstruction and soil structure analysis on the pore scale, and can provide a more intelligent technical method for soil science. [ABSTRACT FROM AUTHOR]

Soil microorganisms participate in the energy flow and nutrient cycle of soil ecosystem, affecting the geochemical cycle process of organisms. Their diversity and community compositions play an important role in determining the function and sustainability of soil ecosystem. The functional diversity of soil microbial community is one of the important indexes to express the soil microbial community and ecological function. Soil microbial diversities of black farmland under different land use types are of great significance to the rational utilization and protection of soil resources. This paper explored the diversity of black soil microorganisms under different land use patterns of farmland, including maize, rice, soybean and potato, and taking the wasteland as the control. The Biolog Eco microplate method and pure culture of bacteria were used to study the changes of soil microbial diversity under four different land use patterns in the black soil area of central and southwest Heilongjiang province. The results showed that: 1) The number of culturable bacteria from more to less were potato, rice, soybean, maize, wasteland, but the variation of Shannon-Wiener diversity index from high to low was: wasteland (2.18), maize (2.11), potato (2.00), rice (1.73), soybean (1.49). 2) The utilization degree of carbon source of microorganisms in black soil under different utilization patterns increased with the extension of culture time. We found that amino acids, carbohydrates and polymers were main carbon sources for the metabolism of microorganisms in black soil. The Shannon-wiener index (3.18), McIntosh index (5.96), richness index (24.89) and Simpson index (0.95) of maize soil microorganisms were higher than those of other land use patterns, among which the diversity index of rice soil microorganisms was the smallest. There was no significant difference between the diversity index of potato, soybean and wasteland. Maize was better suited to the soil environment of farmland in the black soil area of Heilongjiang Province. 3) Principal component analysis identified two principal component factors that were related to carbon sources and explained 54.43% and 7.95% of the variance, respectively. Principal component analysis showed that different land use patterns significantly affects the metabolic diversity of carbon sources in the soil microbial community, and the main types of carbon sources that differentiated the metabolic characteristics of the soil microbial community were carbohydrates, amino acids and carboxylic acids, among which carbohydrates were particularly prominent. It showed that different land use patterns can affect the functional diversity of soil microorganisms. The results of this study is helpful to understand the relationship between soil microbial diversity and land use patterns of farmland in black soil area and provides certain scientific basis for agricultural development and scientific and rational utilization of black soil resources. [ABSTRACT FROM AUTHOR]

China’s coal production accounts for 46.9% of total world coal production, and the annual subsidence area is about 200 km2, which greatly disturbs the soil carbon pool of farmland. As the soil organic carbon (SOC) pool of farmland is the most potential factor reducing carbon emissions from terrestrial ecosystems, China and other major coal mining countries in the world must do better in managing the SOC pool in the coal mining area, which is also an important way for low-carbon coal mining. A spatial prediction method with good prediction accuracy of SOC content in subsidence area of coal mining is the prerequisite of scientific management of SOC pool in coal mining subsidence area. In order to determine a prediction method with high accuracy, taking Jiuli mining area in Xuzhou as a case, this paper predicted SOC content in the study area by the ordinary Kriging and the partition Kriging method. The ordinary Kriging directly spatially interpolated the SOC content based on the regionalized variable theory. In the partition Kriging method, the study area was categorized into non-waterlogged subsidence area, seasonally waterlogged subsidence area and wetland according to the subsidence and water-logging condition in the study area. With the method of partition Kriging, the spatial prediction value can be gained by summing up the mean value of SOC content in each separated area and the predictive residuals through spatial interpolation based on the residual data of the SOC content at each sampling point. Lastly this paper compared the prediction accuracy between the 2 methods with the measured values to determine the better method. It is found that the SOC content obtained by ordinary Kriging ranged from 9.34 to 16.252 g/kg, while the result of the partition Kriging was from 9.333 to 18.058 g/kg. The estimated ranges of the 2 methods were approximately same. Through the comparison, the spatial distribution of the SOC content obtained by ordinary Kriging showed no regularity because of neglecting the smooth transition between regions, while the spatial gradient features of SOC could be enhanced by the partition Kriging. The result showed that the correlation coefficient between the predicted and observed values obtained by the partition Kriging method was 0.7564, which was far higher than that by the ordinary Kriging method (0.5086). The root-mean-square error (RMSE), the mean absolute error (MAE) and the mean error (ME) of 2 methods were 0.35 and 0.55, 1.85 and 1.28, 0.02 and 0.02, respectively. The partition Kriging performed much better than ordinary Kriging as it revealed much lower values of ME, MAE, and RMSE and a higher R2, indicating that the former has higher prediction accuracy. It is concluded that the partition Kriging interpolation model is a more appropriate spatial prediction model for SOC content in coal mining subsidence area, which provides the scientific basis for low-carbon land reclamation in mining area and even utilization of land resources in the region. [ABSTRACT FROM AUTHOR]

Structure characteristic is a typical feature of the unsaturated undisturbed loess, which is an important key factor to affect its strength, deformation properties, and son on, and to distinguish the loess from other special soils. To understand the structure of loess, the key is to find the right way to study the structure. Computerized tomography (CT) technology can detect nondestructively the internal meso-structure in real time, so it is used to be a powerful means for loess structure research. However, it is few reports about the influence of structure on yielding features and the structural evolution characteristics of unsaturated loess during isotropic loading process. In this paper, we took the multifunctional geotechnical triaxial apparatus and the CT technology to research loess structure, and the hydrostatic triaxial compressure tests were carried out by using of 4 undisturbed loess samples whose control matric suction was a constant. When the value of volumetric deformation and water displacement of loess samples reached the expected criteria during loading process, we scanned nondestructively the 4 loess samples with the help of CT technology and got some CT scanning data and images. The structural evolution law of the undisturbed loess during isotropic loading procedure was described by means of the relationship between the macro-scopic mechanical index and the meso-scopic scanning data. In these studies, we found that the structure of undisturbed loess could resist the external load to a certain extent, but the influence of loess structure on yielding characteristic was closely related to matric suction. The CT number increased slowly before sample yielding, however, after sample yielding, the structural effect was reduced obviously and the CT number had a linear growth trend, which indicated that the loess sample entered into the plastic hardening stage. When the suction increased, the structure of undisturbed loess had little effect on the mechanical deformation. When the suction decreased, the water film lubrication between soil particles was obvious, so the effect of the structure fighting against the external load was enhanced obviously. After the net mean stress was applied, the voids and pores of loess samples would decrease, but they would not be closed completely, which was related to the formation of new structures that resisted external loads. According to the CT scanning data, the structural parameters and the structural damage variable were defined during isotropic loading tests, respectively, and then the evolution characteristics of the meso-structure of the undisturbed loess were clarified. In addition, we described accurately the relationships between the structural damage variables and the volumetric strain, and the change of the water phase of loess samples, respectively, and established the damage evolution equation of undisturbed loess structure during isotropic loading procedure. This new damage equation had the characteristics of one parameter and simple form, and could well reflect the influence of the change of solid and liquid phase on the structural damage. The validity of new equation was verified preliminarily by comparison of computation results and test data, which indicated very good agreement between each other. The research results in this paper will provide the reference for establishing the structural constitutive model of undisturbed loess and give a gateway to reasonably analyze loess structure. [ABSTRACT FROM AUTHOR]

Biological soil crusts are fundamental components and surface landscape in arid regions, and biogeochemical process also depends on them. However, biological soil crusts stoichiometry remains largely unknown in the desert region of Northern China. The influences of precipitation on biological soil crusts stoichiometry is also lacking in desert steppe. This paper aims to investigate the effects of precipitation on the stoichiometry of biological soil crusts in desert steppe. This field study was conducted at Dashuikeng Grassland Research Station, Yanchi County (106°58′E, 37°24′N, average elevation, 1 560 m), Ningxia Hui Autonomous Region, China. This region covers a large ecosystem of desert steppe that characterized by low rainfall and uneven precipitation, along the southwest edge of the Mu Us Sandy Land. In the study desert steppe area on the southeastern margin of the Tengger Desert, the average annual precipitation was only 298.3 mm during the 60 years from 1959 to 2019. The precipitation was regulated by the measurement of artificial rain using rainwater shed and sprinkler irrigation technologies, in order to evaluate precipitation effects on the biological soil crusts in desert steppe compared with natural precipitation. 28 precipitation treatments (6 m×6 m) were set up at the test station in early March 2018, where 3 m wide buffer zone was designed between each time. Control conditions of precipitation were designed via the shelter and sprinkler irrigation system, including 7 precipitation treatments, natural precipitation (CK), drought (1/2 reduction in precipitation, DW1/2 treatment, 1/3 reduction in natural precipitation, DW1/3 treatment, 1/4 reduction in precipitation, DW1/4 treatment), and increasing precipitation (1/2 increase in natural precipitation, IW1/2 treatment, 1/3 increase in natural precipitation, IW1/3 treatment, 1/4 increase in natural precipitation, IW1/4 treatment). Each treatment has 4 spares for the reproductivity. In the same period, small weather stations were set up in the test area. TRIME-PICO TDR Portable Soil Moisture Meter (made in Germany) was used for the data collection of precipitation in the soil water depth of 10 cm. Carbon (C), nitrogen (N) and phosphorus (P) contents of biological soil crusts were measured to examine the C: N: P stoichiometry and its driving factors. Three findings can be achieved: 1) Water-reducing treatment was beneficial to the enrichment of C, N and P in the crust. DW1/4 treatment and natural precipitation treatment posed significant effects on the C content in the crust layer and underlying soil. The water-reducing treatment can reduce the N level of the crust, while increase the N level of the underlying surface. The content of P in the crust layer was the lowest under DW 1/3 treatment, whereas the content of P in the underlying surface reached the peak under DW 1/2 treatment; 2) Natural rainfall and increased precipitation can significantly improve the underlying surface C: N and C: P. There was a reduction of N: P in the crust layer and its underlying surface; 3) Suitable soil moisture conditions promoted the accumulation of SMBC (Soil Microbial Biomass Carbon) and SMBN (Soil Microbial Biomass Nitrogen) on the crust layer and underlying surface, while excessive rainfall caused the loss of soil nutrients, which was not conducive to the accumulation of SMBC and SMBN. The relatively dry soil environment was conducive to the enrichment of soil carbon and nitrogen in the crust layer, provided more nutrients for soil microbial respiration, and was conducive to the accumulation of SMBC and SMBN. In short, the C: N: P stoichiometry of biological soil crusts and underlying surfaces had different responses to precipitation in the desertification areas of northern China. [ABSTRACT FROM AUTHOR]

Micro-lysimeter, as a simple and effective method, has been widely used to measure soil evaporation. However, there are still some controversies in its manufacture and application. The objective of this paper is to explore the applicability of micro-lysimeter in measuring soil evaporation under the conditions of bare soil and film mulching in the arid region of Northwest China, and to further analyze the main influencing factors of soil evaporation. The evaporations of bare soil and with plastic film mulch were measured by several micro-lysimeter methods, and sap flow combined with soil water balance method (E(F-B)) was conducted to compare and verify the results. Partial Least Squares (PLS) method was used to evaluate the main factors affecting soil evaporation, and the contribution rates of different factors to soil evaporation were obtained. Results showed it is feasible to measure evaporation of bare soil by micro-lysimeter. The measured results of micro-lysimeters with back cover (sealed) and with gauze cover (unsealed) were similar. The linear relationship between them was E(unsealed)=1.008E(sealed) (R2=0.876 1, P<0.05), The linear relationship between measured results of micro-lysimeters with and without soil replacement was E(no soil replacement) = 0.919E(soil replacement) (R2=0.890 1, P<0.05). Those are suggested that micro-lysimeter with gauze cover (unsealed) and without soil replacement should be adopted in arid areas of Northwest China, since its simplicity, economy and little damage to farmland compared with other micro-lysimeter methods. Evaporation measured by traditional method of ‘evaporation determined by bare soil micro-lysimeter multiplied by hole rate’ (E (LB×HR) was significantly lower than that in the field with plastic film mulch, and the daily evaporation approached 0. There were no significant difference in evaporations measured by micro-lysimeter between with plastic film hole (E(LM)) and bared soil (E(LB)) method, and their average values were 0.96 and 1.24 mm/d, respectively, during the maize whole growth period. It was found that there was a big deviation between E (F-B) and E (LM) method, indicating that the soil evaporation is still large although the farmland is covered with plastic film, which further proves that it is wrong in traditional concepts that the evaporation can be neglected under the condition of plastic film mulching. Although measured evaporation in bare soil using micro-lysimeters was feasible, there would be some deviation using the method in the field with plastic film mulch. Thus evaporation through little mulch hole (0.5%-5.0%) was relative high (1.02 mm/d) and it should not be ignored. Partial Least Squares (PLS) method has been applied in many disciplines and is an effective method to solve the collinearity of independent variables. In this study, contribution rates of different influencing factors to soil evaporation were obtained using PLS method. The contribution values of main influencing factors with Variable Importance in the Projection (VIP) values above 0.8 from high to low in order were: soil water content, solar radiation, leaf area index, hole rate, temperature, and the contribution rates were 23.9%, 18.3%, 17.0%, 14.5% and 13.9%, respectively. [ABSTRACT FROM AUTHOR]

Sandstorm and desertification have posed a worldwide threat to fix quicksand and reduce soil wind erosion for people's living environment. PAM (polyacrylamide), a kind of linear polymer, has been widely used in metallurgy, building materials, paper, mineral processing, oil production, sewage treatment and other industries due to its strong hydration and viscosity, and thereby it is also expected to resist the wind erosion. There is no any toxic effect on soil when spraying PAM solution on the soil surface. The main reason is that the sprayed PAM solution can form hard crust on the soil surface, and then the crust can effectively protect soil from wind erosion. However, the crust condition and wind erosion resistance of PAM are closely related to the PAM application methods, spraying amount and structure of soil. Moreover, high concentration of PAM solution can be a high viscosity, difficult to dissolve or spray, and lead to inconvenient spray on the surface of sand dune or soil. Taking the aeolian sandy soil as test material, this study aims to explore the optimal spraying amount and application method of PAM to prevent wind and fix sand, while reduce water consumption, by tailoring the properties of air-dried soil (aeolian sandy soil) and saturated soil. Specifically, the effects PAM of spraying amounts on surface crust, moisture and soil wind erosion of air-dried soil were investigated to determine the optimal spraying amount of PAM, and then, an optimal amount of PAM was used in the following ways: dry PAM sprinkled, dry PAM sprinkled+spraying water, and spraying PAM solution, to explore a facile method for the application of PAM. The results showed that the soil shear strength, the coverage and thickness of soil crust after PAM treatment increased with the increase of PAM spraying amounts, all of which were significantly higher than that of air-dried soil and saturated soil. The soil moisture after PAM treatment was significantly higher than that of air-dried soil and saturated soil over time. When spraying PAM of 1, 2, 3, and 4 g/m², the wind erosion were 26.83%, 14.10%, 13.01% and 13.00% of air-dried soil, whereas, 28.78%, 15.12%, 14.02% and 13.94% of saturated soil, respectively. When the spraying amount of PAM reached 2 g/m², PAM can effectively reduce the wind erosion of aeolian sandy soil. After 2 g/m2 dry PAM sprinkled+spraying water and spraying, the coverage and thickness of soil crust, and soil shear strength were higher than that of air-dried soil, saturated soil and dry PAM sprinkled. In dry PAM sprinkled treatment, the coverage of soil crust was lower than that of saturated soil, but higher than that of air-dried soil, whereas, the thickness of soil crust and soil shear strength were higher than that of air-dried soil and saturated soil. In dry PAM sprinkled+spraying and spraying PAM solution, the soil moisture was higher than that of air-dried soil, saturated soil and dry PAM sprinkled. In dry PAM sprinkled, the soil moisture was basically the same as that of air-dried soil. The soil wind erosion after dry PAM sprinkled, dry PAM sprinkled+spraying water and spraying PAM solution were 53.13%, 11.17% and 6.35%, of air-dried soil, respectively, and 76.34%, 16.05% and 9.12%, of saturated soil, respectively. In the dry PAM sprinkled+spraying water, the resistance of wind erosion was close to that in the spraying PAM solution on the surface of aeolian sandy soil. In order to save water and manpower when preparing and spraying the PAM solution, two measurements were proposed. One is that 2 g/m² PAM powder can be dry sprinkled on the surface of sand dunes and soil before rain in the wind-sand areas according to weather forecast. Another is, after dry PAM powder sprinkling, the sprayed water on the surface of sand dunes and soil can effectively fix the quicksand and reduce the amount of soil wind erosion. [ABSTRACT FROM AUTHOR]

Widespread soil acidification in China has posed a series of severe problems on agriculture ecosystems. In previous control measures, the use of lime can lead to soil hardening, whereas, industrial alkaline wastes inevitably face the risk of secondary pollution. Recently, cheap dolomite can be expected to serve as a soil functional conditioner, particularly for providing adequate amounts of calcium and magnesium nutrients for crops. This paper aims to investigate the effects of particle size and calcination time on dolomite alkalinity, microstructure, and release kinetic characteristics of calcium and magnesium during a low temperature calcination process. Two concepts were proposed, the capacity of alkalinity and short-term cumulative alkalinity, in order to evaluate the acid treatment of calcined dolomite. The results showed that after the calcination of dolomite with a particle size less than 3mm, the capacity of alkalinity increased by 78%, and the short-term cumulative alkalinity increased by 1 100 times, whereas the calcination time was extended from 1 hour to 3 hours without significantly increasing the total alkalinity. After calcining dolomite with a particle size of 0.15 to 0.25 mm, the release rate of calcium and magnesium reached the maximum after 3-hour calcination. However, the calcined dolomite with a particle size of 1 to 3 mm indicated a stable release rate of calcium and magnesium after the calcination for 1 to 3 hours, and the maximum release rate occurred after the calcination for 2 h. After 26 days incubation, the cumulative release rate of calcium in the calcined dolomite was over 87%, and the cumulative release rate of magnesium was less than 9%. Release curves of calcium and magnesium from calcined dolomite can be fitted using parabolic, first order kinetics, Richards and Bertallanffy equations. The modified Bertallanffy equation can be the most suitable to describe the release change of CaO amount from calcined dolomite over time, where r = 0.990-0.999, SE=0.47-1.53. Richards and the modified Bertallanffy equations can be used to quantitatively describe the MgO release pattern of dolomite, or predict the amount of magnesium supplied by dolomite. The goodness of fit test of the Richards equation was r=0.959-0.985, SE=0.14-0.20, while that of the modified Bertallanffy equation was r=0.980-0.993, SE=0.13-0.19. It infers that the calcined dolomite can serve as high capacity and intensity of alkaline, total and short-term cumulative alkalinity, while the calcination process can promote the release or supply of calcium and magnesium, where the release rate can be predicted by using Richards and modified Bertallanffy equations. In the calcinated dolomite with a large particle size of 1 to 3 mm, 1 hour can be an economical calcination time to increase its capacity of alkalinity, whereas the optimum is 2 hours calcination process to promote rapid cracking, short-term cumulative alkalinity, effective calcium and magnesium. The research results can provide a theoretical basis for calcinated dolomite translating to serve as soil conditioner and its manufacturing process. [ABSTRACT FROM AUTHOR]

Study on changes in microscopic structure of saline-alkali soil induced by different land usage in the Yellow River Delta is important to understand their consequence for soil mechanical and hydrological processes and improve soil management and remediation. This paper presents the results of an experimental study on microscopic structure of soils taken from farmland, grassland and beach at different soil depths in this region. The particle size and mineral composition of each soil sample were measured using the particle size distribution analysis and X-ray diffraction analysis, respectively. The poresize distribution was analyzed using mercury intrusion porosimetry, and soil particle arrangement and pore characteristics were measured using scanning electron microscopy (SEM). The results showed that the main particles of the three soils were silt, accounting for more than 60% of the total particle composition. The clay content in the three soils increased in the order of farmland > beach > grassland. Primary minerals such as quartz, calcite and albite were dominant in the three soils, accounting for more than 85% of their total mineral composition. The clay minerals in the three soils were dominate by illite, and the proportion of the clay minerals was less than 15% of the total mineral composition. The clay mineral content was higher in the farmland soil than in the grassland and beach soils and, as such, the mineral composition alone cannot explain the low permeability of the soils. The porosity of the farmland, beach and grassland soils was 25%, 32.58%-39.94% and 40.84%46.16% respectively. With increasing depth, the porosity of the grassland and beach soil increased, whereas the change in farmland soil porosity did not show an identifiable trend. The pore characteristics of the grassland and beach soils were similar, while the farmland soil was dominated by micropores and ultra-micropores with pore diameter less than 2 µm. The specific pore surface area of the farmland soil was considerably larger than that of grassland and beach soils, with the adsorption capacity of the former much higher than that of the latter. Farmland soil was densely structured; it was dominated by micro-fissures, with disordered structures formed between the skeleton particles; its basic structural units were flat and flaky particles; the skeleton particles ware dominantly surface contact while the particles were cemented by clay minerals. The microstructure of the grassland soil was closely inlaid particles with a "brick-wall" arrangement, and the particle connection was mainly surface contact; it was composed of closely inlaid massive particles and overhead pores; there was no cementation between its skeleton particles. The beach soil was composed of closely accumulated granular particles and intergranular pores; there was no cementation between skeleton particles. These results improved our understanding of the changes in microscopic structure of saline-alkali soils in response to land usage in the Yellow River Delta. They provide guidance for remediation, utilization and development of coastal saline-alkali soil in the Yellow River Delta. [ABSTRACT FROM AUTHOR]

The change process of cultivated layer quality for slope farmland at plot scale is influenced by the interactive effects between erosive rainfall and artificial farming activities at different temporal and spatial scales. For a slope surface, there exists a successive erosion process of rainfall-runoff-infiltration and the consequence is first reflected in the quality of cultivated layer. Among the factors induced the erosion process at plot scale, terrain is an important factor because it could redistribute the ratio of rainfall--infiltration, which directly cause a different erosion process for an erosive rainfall and the different degradation degree during a rainy season and a growth season. Taking purple soil slope farmland as an example, the paper firstly analyzed the varying characteristics of cultivated layer quality of slope farmland, then quantitatively evaluated the effects of four terrain factors, altitude, slope angle, effective soil thickness and slope position on cultivated layer quality and their sensitivity of impact, adopted principal component analysis and evaluation model. The results indicated: 1) Such soil properties as cultivated layer thickness, soil organic matter and soil bulk density of cultivated layer were all within the suitable scope and soil nutrient properties were generally at middle & low levels. The variation coefficients of soil bulk density and soil total porosity showed weak variability (CV<10%), presenting 7.97% and 8.36% respectively and the other soil properties showed moderate variability. 2)Minimum data set for cultivated layer quality evaluation of purple soil slope farmland consisted of eight soil parameters, bulk density, penetration resistance, soil organic matter, clay content, cultivated layer thickness, soil shear strength, saturated water conductivity and bioavailable phosphorus. Soil physical properties are more important than chemical properties except soil organic matter for erosion control and crop growth of slope farmland. Evaluation based on the MDS revealed that the cultivated layer quality varied spatially over the slope, being 0.458 in the low part of the slope, 0.443 in the middle part of the slope and 0.417 in the upper part of the slope and the quality value of the lower slope was 3.39% and 9.83% higher than that of the middle slope and upper slope positions, respectively. 3) The factors affecting cultivated layer quality divided into four types: slope-angle impacted type, slope location impacted type, effective soil layer thickness impacted type and altitude impacted type and they accounted for 38.89%, 22.22%, 14.81% and 24.08% of the total samples taken from slope farmland respectively. The slope angle was the main determinant of cultivated layer quality because it could induce directly many ecological processes at plot scale. The slope angle and effective soil layer thickness could be modified by such soil and water conservation measures as terrace, biological ridge and soil improvement methods. But the slope location and altitude could not be modified easily only by selecting suitable crop system. 4) The quality of cultivated layer had positive correlation with its thickness and location in the slope, and negative correlation with altitude and slope angle. Sensitivity analysis revealed that the determinants were ranked in the order of altitude (-0.399) > location in the slope (0.192) > slope angle (-0.112) > effective soil layer thickness (0.110) based on their impact on cultivated lay quality. These results could provide some useful evaluation parameters and its regulating direction for cultivated layer quality, which contributed to the sustainable utilization of purple soil slope farmland. Furthermore, other samples of slope farmland should be studied in order to find out the critical values of MDS according to 2 functions of cultivated layer, erosion control and soil productivity. [ABSTRACT FROM AUTHOR]

In order to study the characteristics of microplastics and its response relationship with mulching years, irrigation methods in the farmland soil of Hetao Irrigation District, field sampling and indoor experiments were used in combination for in-depth study. This paper mainly analyzed the current situation of plastic film mulching in Hetao Irrigation District by considering the effects of mulching years (5, 10, 20 a) and irrigation methods (drip irrigation and surface irrigation under film mulching). The abundance, type, color, particle size and other distribution characteristics of microplastics in the farmland soil were analyzed and other microplastic surface features and attachments also were observed and discussed, which was supported by scanning the electric microscope and energy spectrometer. The results showed that the average abundance of microplastics in soil under the different mulching years (5, 10, 20 a) in Hetao Irrigation District was 2 526.00, 4 352.80, 6 070.00 pieces/kg. The maximum microplastic was 2133.50 pieces/kg in every layer of soil appeared at 0-10 cm soil layer by mulching 20 a, and the minimum microplastic was 678.00 pieces/kg at 20-30 cm soil layer by mulching 5 a. The average annual increasing rate of microplastics was 14.46% in the early stage (5-10 a), while the increasing rate in the later stage (10-20 a) was 3.95%. The abundance of soil microplastics was affected by different plastic-mulching years and irrigation methods. The abundance of microplastic in drip irrigation farmland was slightly larger than the surface irrigation farmland, and it decreased with the increase of soil depth. By further analysis, the major categories of microplastics were fibers (23.34%), fragments (26.31%), films (38.57%) and grains (11.78%); the colors of microplastics included black, transparent, green, red, blue, etc., with the proportions 24.56%, 23.83%, 19.34%, 16.52% and 15.75% respectively. In the 0-10 cm soil layer, the main color of microplastics was black and it accounted for 30.25% of the total microplastic; in the >10-20 and >20-30 cm soil layer, the main color of microplastics were transparent, accounted for 30.15% and 29.23% of the total microplastic. The particle size exhibited a downward trend with the increase of the mulching years, and the majority of particle size less than 1 mm. In addition, with the increase of mulching years, microplastics particle size in >0-10, >10-20, >20-30 cm soil layer was gradually decreased, and there was no significant relationship between size and irrigation method (P>0.05). The surface features of microplastic samples were rough and irregular pores existed on it, and fiber, thin film and fragments microplastics had regular micropores, while the grain microplastic surface pores were irregular and concave. The porous properties of microplastics in soil made the characteristic of greater specific surface area carried by it. This characteristic could increase the adsorption of other pollutants and microorganisms from the soil; and there were stable iron oxides and rare earth elements on the surface. The research is of great significance to clarify the distribution and harm of microplastics in the soil of the Hetao Irrigation District. [ABSTRACT FROM AUTHOR]

The effect of high concentration sodium salt solution infiltration in reclaimed water on soil hydraulic characteristics is one of the key problems of soil ecological environment degradation caused by long-term low-quality water irrigation. In this paper, the hydrodynamic parameters of 5 kinds of subtropical soil, such as clay fluvo aquic soil, sandy fluvo aquic soil, red soil, paddy soil and purple soil, were measured by constant head penetration method and one-dimensional horizontal soil column imbibition method. The influence of sodium salt solution concentration on the hydraulic properties of soil was investigated, and the mechanism of the physical and chemical properties of soil affecting the hydraulic conductivity was analyzed. The results showed sodium slat solution infiltration could enhance soil wet front migration rate of clay fluvo aquic soil, sandy fluvo aquic soil and paddy soil maximally by 33.0%, 32.5% and 93.5%, lower that of red soil maximally by 34.8%. The soil clay content, exchangeable iron and aluminum content mainly inhibited soil water movement, while silt content, exchangeable calcium and magnesium content promoted soil water movement. Sodium salt accelerated water movement in clay fluvo aquic soil, sandy fluvo aquic soil and paddy soil. Relative soil water diffusivity increased by 22.0%, 37.3% and 39.7% respectively. Sodium salt inhibited the water diffusion of red soil and purple soil. The higher salt concentration could result in the smaller relative soil water diffusivity. At 15 g/L salt concentration, the soil water diffusivity decreased by 30.5% for red soil and 42.1% for purple soil, respectively. Relative soil water diffusivity of clay fluvo aquic soil, sandy fluvo aquic soil, red soil and purple soil fluctuated with the increase of soil water content, while the relative soil water diffusivity of paddy soil decreased with the increase of soil water content. Relative soil water diffusivity of paddy soils showed a good parabolic relationship with salt concentration (R²=0.987), while red soils and purple soils showed a good linear relationship with salt concentration (R²>0.933). The saturated hydraulic conductivity of clay fluvo aquic soil treated with sodium salt solution increased most obviously, with a maximum increase of 77.3%, followed by paddy soil, with a maximum increase of 25.1%. With the increase of salt solution concentration, the relative saturated hydraulic conductivity of soil decreased first and then increased. In the range of 1-10 g/L salt concentration, the saturated hydraulic conductivity of soil had a good parabolic relationship with the sodium salt concentration (R² was not less than 0.807), and the saturated hydraulic conductivity of soil was the smallest when the concentration of each extreme point of soil was about 5 g/L. Therefore, the salt concentration of reclaimed water should be moderately controlled to a level lower than the extreme point concentration. [ABSTRACT FROM AUTHOR]

Shajiang black soil is a typical middle and low production soil in Huang-Huai-Hai Plain. Crop production has been seriously restricted due to the high clay contents and low available water capacity of Shajiang black soil, this paper studied the effects of different modified materials on soil water holding capacity and wheat physiology of anti-drought stress by wheat pot experiment carried out in March 2018, in order to provide technical supports for farmland water managements. According to local field fertilization and water management modes, 4 treatments were designed in wheat pot experiment: chemical NPK fertilizer (CK), chemical NPK fertilizer with maize straw returning (SR), chemical NPK fertilizer with maize straw carbon (SC), and chemical NPK fertilizer with fly ash (FA). Referring to conventional amount of applying fertilizer in northern farmland in Anhui province, the application amounts of chemical fertilizer were 225 kg/hm² (N), 120 kg/hm² (P2O5), and 60 kg/hm² (K2O), respectively, and the application amounts of fly ash, maize straw carbon, and maize straw returning to field were 45×10³ kg/hm², 45×10³ kg/hm² and 6×10³ kg/hm², respectively. As for wheat pot experiment, in each pot, about 10 wheat seeds were transplanted into 30 kg soil after accelerating seeds germination. Soil relative water content was maintained at 80% field capacity until heading stage. When wheats grew up to the heading stage, irrigation stopped and then a drought stress experiment was carried out for 10 days. Wheat leaves collected regularly were stored at -80 ℃ so as to determine wheat physiological and biochemical index. The results showed that both SC and SR improved soil water holding capacity, but both was not significantly different. Owing to the abundance of large amount of hydrophobic crystal minerals like the crystallographic silicon dioxide in the surface of fly ashes, FA had a fast decrease in relative soil water content. The delayed water content of FA was significantly lower than the other treatments, while the available water content was significantly improved. What’s more, different modification materials all had the tendency to increase saturated water content and alleviate the impairments of wheat leaves caused by drought stress. Under mild drought stress, the saturated water content of wheat leaves was higher than that of the control group, but no significant difference was found in the contents of proline (PRO), malondialdehyde (MDA), hydrogen peroxide (H2O2) and peroxide scavenging coenzyme in the wheats among the four treatments. However, under extreme drought stress, not only was FA significantly lower than the other treatments in wheat leaves saturated water content, but also FA treatments accumulated more harmful substances like MDA and H2O2 in wheats, which could lead to irreversible damages to wheat physiological conditions. In conclusion, the relative water content of Shajiang black soil was suggested to keep above 38% (SR), 36.5% (SC) and 24.5% (FA), respectively. The plant physiology would get irreversible damage if relative soil water content was under 30.78% (SC), 28.43% (SR) and 22.5% (FA), respectively. Because straws have better performance in holding water by significantly improving the content of soil capillary pore, and fly ashes can do better in providing more available water for soil in spite of holding water poorly, combined application of straws and fly ashes will be conducive to the improvement of Shajiang black soil. Relevant mechanism need to be furtherly studied. [ABSTRACT FROM AUTHOR]

In order to quantitatively analyze the relationship between the phreatic evaporation and water surface evaporation of different soil textures in bare soil area, soils with different texture and sand samples were taken from the test site in Hefei University of Technology. After pretreatment such as drying and particles sieving, 4 types of homogeneous test materials were selected including coarse sand, fine sand, loam and sand soil. Then, a self-made phreatic evaporation measurement device was made with diameters of 60 and 25 mm and a height of 42 mm. It can easily solve the problem of automatic water replenishment during the evaporation process, so that the groundwater depth can always be 0. Based on the self-designed device, a total of 5 groups of comparative test schemes were constructed, including coarse sand, fine sand, loam, sandy soil and water in bare soil area. Under the same environmental conditions, daily phreatic evaporation of the 4 different soil textures and water surface evaporation were observed for a total of 127 days from December 24, 2018 to April 29, 2019. By analyzing the relationship between phreatic evaporation and water surface evaporation for soils with different textures, linear mathematical equations were established. The results revealed that the change trend of phreatic evaporation and water surface evaporation was basically the same during the experiment. The high air temperature would lead to larger soil evaporation. However, the phreatic evaporation of the 4 different soil textures was not equal to the water surface evaporation, and the difference between them was more significant as the air temperature was increased. The determination coefficients between phreatic evaporation value of different soil textures and the water surface evaporation were all greater than 0.97. Especially for fine sand, the correlation coefficient reached 0.99, which indicated that there was a significant correlation between phreatic evaporation and water surface evaporation (P<0.05). And the conversion coefficients were achieved between them according to the linear mathematical equations. Generally, in soil bare areas with similar climatic conditions in Hefei, the conversion coefficient of coarse sand was 0.94, and the coefficients of fine sand, loam and sand are 1.04, 1.14 and 1.19, respectively. The phreatic evaporation value of coarse sand was less than the evaporation of water surface. The phreatic evaporation values of fine sand, loam and sand were greater than water evaporation. Under bare soil conditions, this conversion coefficient was only related to soil texture. In addition, the loam and sandy soil evaporation in the Wudaogou test site of Anhui Province, China was selected to verify the rationality of the conversion coefficient obtained above. The results showed that when the groundwater depth was 0.4 m, the relative error of the loam evaporation calculated by the substitution method and the phreatic evaporation coefficient method were -10.30% and 2.25%, respectively. Moreover, the sand evaporation calculated by the substitution method was 5.11 mm smaller than the measured value with a relative error of -17.79%, while the sand evaporation calculated using the phreatic evaporation coefficient method was only less than the measured value of 0.56 mm, and the relative error was reduced to -1.94%. Therefore, when calculating the phreatic evaporation at different groundwater depths, directly replacing phreatic evaporation with water surface evaporation would inevitably cause larger relative errors. However, the relative error of the calculation result obtained from the phreatic evaporation coefficient method was smaller, and the calculated value was much closer to the measured value. The coefficient method proposed in this paper would significantly improve the reliability and accuracy of the calculation results of phreatic evaporation. [ABSTRACT FROM AUTHOR]

The soil contamination by heavy metals is one of the increasingly serious environmental issues worldwide, and it is believed to pose a high risk to natural environments and human health when their accumulation exceeds certain levels. Optimum sampling numbers in a sampling unit can be an effective tool to achieve credible results when surveying heavy metals in topsoil and undertaking risk assessment for sustainable land uses or remediation decisions. Based on a large amount of literatures and available data in the recent years, the current situations of sampling numbers, methods on determining optimum sampling numbers for survey of soil heavy metals were reviewed in this paper and future research issues in this area were discussed. Also, based on empirical methods (e.g. purposive sampling), statistics (including different methods under the normal distribution and lognormal distribution) and empirical methods combined with statistics (e.g. multi-stage sampling), the merits and demerits of these methods on determining optimum sampling numbers for survey of heavy metals in topsoil were then systematically analyzed and compared. The results showed that there were some challenges or issues. First, the consideration of sampling scales or sampling units was lacked when determining optimum sampling numbers for survey of soil heavy metals. Second, researches for determining optimum sampling numbers were more focused on the empirical methods, but there were few by statistics or empirical methods combined with statistics. When determining optimum sampling numbers by statistics, they were more focused upon the methods under the normal distribution, such as classical statistics, geostatistics and simulated annealing algorithm. However, their usefulness was often limited because there was adequate empirical evidence and a theoretical proof to illustrate that the distribution of soil heavy metal content often approximately followed a lognormal distribution. The application in determining optimum sampling numbers for survey of soil heavy metals under the lognormal distribution, which has little been reported to date. Third, although some scientists proposed the methods to determine optimum sampling numbers under the lognormal distribution, including the Land’s accurate method and other correction equations of this accurate method (such as Hale’s method, Armstrong’s method, classical lognormal equation, quadratic term approximate equation and Chebyshev inequality), the Land’s accurate method under the lognormal distribution was too complex because of the need for computing by an iterative algorithm and requiring extensive tables. The different correction equations had been limited because they not only were not enough to cover the different coefficient of variation of soil heavy metals, but also overestimated or underestimated the optimum sampling numbers. Moreover, these mentioned different methods under the lognormal distribution had not been applied to estimate the optimum sampling numbers for survey of soil heavy metals. Therefore, sampling scales or sampling units of soil heavy metals were defined when determining optimum sampling numbers. The researches on determining optimum sampling numbers by statistics and empirical methods combined with statistics were strengthened. The accurate methods on determining optimum sampling numbers under the lognormal distribution were explored. The methods suited for determining optimum sampling numbers for survey of soil heavy metals in a sampling unit were sought. These were important guarantees to achieve scientific risk assessment, effective environmental decision-making and pollution control of soil heavy metals. [ABSTRACT FROM AUTHOR]

Wheat straw returning is one of the main ways to improve soil fertility. Long-term straw returned to field combined with chemical fertilizer can maintain soil fertility. It should be combined with crop rotation system and fertilization management to maximize advantages and avoid disadvantages. The impact of straw returned to field on crop yield and how to fertilize when straw returning are the issues of great concern to agricultural producers. In order to clarify the effect of long-term straw returned to field in wheat-bean rotation on crop yield and soil nutrient, this paper conducted the experiments in the long-term positioning experimental station in Heihe district of Heilongjiang province, and adopted split-plot test method. The main treatment was straw returning to field and non-returning to field, secondary treatment was different fertilization for low, medium and high level. The experiment started in 1980 with wheat-soybean-wheat and wheat-soybean rotation models. The effects of wheat straw returning to field and different fertilization levels on crop yield under wheat-soybean rotation conditions were investigated for 38 consecutive years (1980-2018). The results showed that there was no significant difference in years of yield of wheat, soybean or wheat planted every other year after wheat straw returning. The medium-fertilizer was 7.42%-10.81% higher than that of low-fertilizer area on soybean with continuous fertilization, achieved significant difference level. The yield of wheat increased by 14.52%-19.33% in high-fertilizer area compared with low-fertilizer area. The effect of wheat straw returning on soybean yield was 5.91% higher than that of non-returning in the early stage (1-6 season) and 7.52% higher in the late stage (7-16 season). The yield of wheat increased by 0.31% and 0.22% in early stage (1-5 seasons) and late stage (6-16 seasons) compared with non-returning to field. Generally speaking, after wheat straw returning to the field, the frequency of crop yield reduction in the early stage is high, while the frequency of yield increase in the later stage is high. In Heihe area, the long-term application of wheat straw to field had no significant effect on soil organic matter, total nitrogen, alkali nitrogen, total phosphorus, available phosphorus and total potassium, while the content of available potassium increased significantly. Long-term fertilization had a significant impact on soil nutrients. High fertilizer level could significantly increase the contents of soil organic matter, total nitrogen, alkali nitrogen and total phosphorus. Long-term fertilization also reduces soil pH value, leading to acidification of soil. [ABSTRACT FROM AUTHOR]

Complex soil erosion is an erosion phenomenon that occurs under the interaction or coupling of two or more erosive forces, and is one of the most difficult ecological problems to be managed. In recent years, remarkable progress has been made in the mechanism of complex erosion, the effect of complex erosion on soil degradation, and the simulation technology of multi-dynamic erosion interaction. Based on previous research, this paper systematically summarizes the research progress of the types and characteristics, mechanism and research methods of complex erosion. The main problems in the research are analyzed, and some key scientific problems to be solved in the future research on the law of complex erosion and the method of simulation test are put forward. Due to the obvious spatiotemporal heterogeneity and the complexity driven by multi dynamics in complex erosion, the existing research results are still quite different, and the dynamic mechanism of the occurrence and development of complex erosion is still unknown. The research on theory and method of complex erosion simulation and quantitative assessment is still very weak. In particular, there is a lack of effective test key technology to reveal the multi power driving relationship. At present, the problems in the study of complex erosion mainly include: 1) The multi-dynamic interaction relationship in complex erosion is not studied as a complete dynamic system; 2) The spatial-temporal variation relationship between complex erosion process and environmental factors is not clear enough; 3) It is still a key problem to quantitatively identify the contribution rate of each driving factor in the process of complex erosion; 4) The quantitative research on the coupling and superposition of multi dynamic factors in the process of complex erosion is not enough. In the future, the dynamic mechanism of the occurrence and development of complex erosion and the simulation of multi dynamic decomposition will become the key research direction. Therefore, it is necessary to clarify the complex erosion model under multi dynamic interaction, clarify the feedback mechanism of vegetation pattern on complex erosion, reveal the coupling mechanism of ecosystem degradation and complex erosion under multi dynamic stress, establish the identification method of the coupling relationship between multi dynamic complex erosion and sediment yield, and break through the theory and technology of complex erosion simulation. This will promote the development of complex erosion research from qualitative to quantitative, from process to mechanism, and will greatly enrich the research content of soil erosion dynamics, ecology and other related disciplines. We should focus on the following research directions: the simulation technology of rainfall-wind tunnel-freeze-thaw multi-dynamic alternating cycle test based on multi-source data fusion, quantitative evaluation technique and method for driving factor in compound erosion system, identification and quantification of sediment yield process under different coupling conditions of multi-dynamics in order to provide reference for related research. [ABSTRACT FROM AUTHOR]

The investigation site is located in Jinggouxing watershed (from 26°10′31″N to 26°12′33″N and115°9′3″E to 115º11′39″E) in the north of Gan County, Jiangxi Province, China. The soil type is mainly red soil developed by granite. The collapsing gully area is 95.8 hm², which belongs to the intensity erosion area of the hills and mountains in the south of Jiangxi. Due to the sudden, violent, serious damage, and difficult to manage characteristics of collapsing gully, it has severely affected the local ecological environment and residents' lives, so it has become an important research direction for soil and water conservation. Collapsing gully is affected by hydraulic and gravity erosion. Among them, the hydraulic erosion of collapsing gully is mainly affected by surface runoff. The instability of the collapsing gully wall gradually increases through the undercutting effect of runoff, and then develops under the combined action of hydraulic and gravity erosion. Soil infiltration is the premise and basis of surface runoff. By analyzing the infiltration characteristics of collapsing gully soil, we can further understand the process of soil erosion by collapsing gully soil. In recent years, the disc infiltration meter has been widely used to determine soil hydraulic characteristics due to its fast and easy operation. In this paper, a disc infiltration instrument was carried out under four pressure heads (-9, -6, -3, and 0 cm) on the collapsing gully soil at three different developmental stages (initial stage, active stage and stable stage) and three parts (catchment, slope and channel). The basic physical and chemical properties of collapsed hills at different developmental stages were studied, and the correlation between the developmental stages and parts of collapsing gully to the basic physicochemical properties was analyzed. The variation of soil infiltration rate with different infiltration heads at different developmental stages and parts of the collapsing gully was plotted. According to the measured values of soil hydraulic conductivity and Gardner's constant α, the effects of collapsing gully at different developmental stages and their parts on the soil hydraulic conductivity and soil pore classification contribution to flow were analyzed. The results showed that soil infiltration properties were affected by soil sand content, pressure head, soil pore size distribution, soil erosion and space parts. The higher the sand content in the soil, the more severe the soil erosion would be, which would affect the soil infiltration characteristics. When the pressure head was 0, the stable infiltration rate at the collapsing gully in the developmental stable period was the highest, 1.01 and 1.40 times higher than that in the collapsing gully at the initial stage and active stage of the collapsing gully. With the decrease of the pressure head, the stable infiltration rate of the soil in the three different developmental stages gradually decreased. The soil hydraulic conductivity of different parts of the collapsing gully was basically similar under different pressure head conditions. There was no significant difference in soil hydraulic conductivity and Gardner's constant α at three different developmental stages. Except for the hydraulic conductivity at a pressure head of -9 cm, the soil hydraulic conductivity and the Gardner constant α values at different parts of the collapsing gully were significantly different. As the degree of erosion increased, the contribution rate of macropores to flow at different developmental stages increased. The parts of collapsing gully significantly affected the contribution rate of macropores, mesopores 2 and micropores to flow, it could be seen that the part of collapsing gully was an important factor which affected the hydraulic properties of soil. The results could provide some references for the soil erosion process of the collapsing gully soil at different developmental stages in the southern china [ABSTRACT FROM AUTHOR]

Engineering accumulations are usually poor in soil structure and susceptible to erosion and corrosion, especially when the slope is steep. These could endanger their ecological functions and result in environmental hazards. How to improve ecological functions and alleviate soil erosion of earth slopes is pressing. The objective of this paper is to experimentally study the efficacy of different vegetation patterns in regulating water and sediment erosion of slopes under different water flow conditions. The experiment was conducted in the field at the Linghou Experimental Station, Institute of Soil and Water Conservation, Chinese Academy of Sciences (34°19′24″ N, 107°59′36″E). In the experiment, we analyzed the efficacy of five grass coverage patterns: upper coverage, middle coverage, low slope, band, and no coverage under four upslope runoff patterns (constant, earlier peak, medium peak, later peak). The experimental slope was a 20 m×1 m plot 0.5 m thick excavated from a slop; The slope angle was 32o. We used the fractal dimension of the eroded sediment particles to quantify the change in soil erosion, the enrichment rate (ER) to describe the difficulty associated with migration of eroded particles of certain size group, and the agglomeration rate (AR) to describe the ways that the surface runoff carrying the eroded particles of certain size group. The results showed that: 1) The relationship between soil denudation rate and the runoff power follows power function model (R²=0.47-0.72，P<0.01), and that the runoff power was the optimal parameter to describe the erosion dynamics of the slope. 2) Runoff can be reduced by 12.23%-49.62%, and sediment can be decreased by 12.92%-80.54% under vegetation patterns, the sediment reduction effect of vegetation pattern was higher than runoff reduction. The average runoff and sediment reduction benefit of the band and upslope patterns was 43.87%, 58.09% and 30.55%, 54.41%, respectively, which were significantly better than other vegetation patterns. 3) Compared with the control plot (without grass coverage), the volume percentage of sand particle in sediment of the vegetation plots was reduced by 18.79%-35.80%, the volume percentage of clay was increased by 3.56%-10.69%, which indicated that the interception effect of vegetation on sand was significant. Volumetric fractal dimension of the eroded particles was dominated by the volumetric fraction of clay and they were linearly correlated at significant level (R²=0.90，P<0.01). 4). Compared with the control, grass coverage reduced the sand enrichment rate, but increased the clay enrichment rate; their associated volumetric fractal dimension also increased. Clay and sand in the eroded sediments were in the forms of agglomerates, while the silts moved mainly as single particles. Our study has an important implication for ameliorating soil erosion from engineering accumulation. [ABSTRACT FROM AUTHOR]

Soil respiration is mediated by microbial activities, temperature, humidity and other environmental factors in soil. The increase in use of microbial organic fertilizer and drip irrigation in greenhouse production could alter soil micro-environment, particularly the rhizosphere, thereby leading to a change in soil respiration. This paper investigated the response of soil respiration to different combinations of drip irrigation amounts and microbial organic fertilizer applications. We experimentally compared three irrigation amounts 15, 18 and 21 mm – associated with three microbial organic fertilizer applications 2800, 3600 and 4400 kg/hm². The treatment with inorganic fertilizer application served as the control. In each treatment, we measured soil respiration rate and accumulated carbon emission, as well as other determinants. The soil temperature and humidity were measured following the soil respiration measurement using the delta-T sensor (delta-T company, UK); soil organic matter was measured using the potassium dichromate sulfuric acid oxidation external heating method; the activity of dehydrogenase was determined using the TTC colorimetry method; the activity of urease was determined by the phenol sodium colorimetry method; the activity of catalase was determined by the KMnO4 volumetric method. We analyzed the responsive change in soil respiration to these determinants and root biomass. The results showed that, compared to the CK, drip irrigation and microbial organic fertilization improved soil organic matter and increased the activities of dehydrogenase, urease and catalase by 11.6%-27.6%, 8.0%-27.7% and 1.8%-11.2%, respectively; the increase in urease activities was at significant level (p<0.05). The soil respiration rate was positively correlated to the root biomass, temperature and organic matter content at significant level of p<0.01, and to the enzymatic activities at significant level of p<0.05. Among all treatments, irrigating 18 mm of water and applying 4400 kg/hm² of microbial organic fertilizer produced the highest root biomass, reaching 394 g/m² 120 days after the transplanting. Overall, combining drip irrigation and microbial organic fertilization increased root biomass by 25.9%-43.4%, compared to the CK. When irrigation amount was 15 and 18 mm, the carbon emission increased significantly (p<0.05) when the fertilizer application increased from 3600 kg/hm² to 4400 kg/hm². The cumulative carbon emission peaked at 415.2 g/m² when the irrigation amount was 18 mm and the microbial fertilization was 4400 kg/hm², significantly higher than that under other treatments (p<0.05). The lowest cumulative carbon emission was from the CK, being 255.3 g/m² only. In summary, this study showed that drip irrigation and microbial organic fertilization combined to impact soil carbon emission by changing organic matter content and root biomass in the soil. Our results have important implications for improving ecological cultivation in greenhouse production. [ABSTRACT FROM AUTHOR]

In order to improve the efficiency and accuracy of the quantitative prediction of soil nutrient content in black soil of Heilongjiang province, in this paper, we utilized statistical theory and spectral analysis method, researched the relationship of three kinds of soil nutrient content and soil spectrum to established hyperspectral inversion model of soil total nitrogen, available phosphorus, available kalium content. We acquired the aerial hyperspectral data by using CASI-1500 and SASI-600 linear array push-broom imaging spectrometers. Preprocessing of calibration and atmospheric radiation correction of Airborne Hyperspectral raw radiation data was studied. 96 samples were evenly sampled. In order to increase the representativeness of samples, 96 groups of samples were collected from 3-5 samples collected from 15 meters around the sampling point, and 1.5 kg was retained after mixing. After air-drying, mixing and grindingetc, it is used for the contents of total nitrogen, available phosphorus and available kalium were obtained through laboratory tests. The content of total nitrogen, available phosphorus and available kalium was determined by NaOH diffusion method, NaHCO3 extraction-molybdenum blue colorimetry and NH4OAC extraction-flame photometry. Referring to Kennard-Stone method, 72 groups of representative samples were selected as model samples for nutrient content prediction, and 24 groups were model prediction samples. 96 black soil samples were sorted according to nutrient content, and the spectral transformation in the visible near red range was analyzed. The change rule of total nitrogen is that the reflectance decreases with the increase of content. The first order differential spectra at 580 nm were significantly correlated with total nitrogen and available phosphorus content, with a correlation coefficient of -0.43 and -0.36, respectively. The first-order differential spectra at 1730-2200 nm were significantly correlated with K2O, and the maximum correlation coefficient was -0.31. Compared with the original spectral waveform, the correlation coefficient between the first derivative and three nutrient contents fluctuated sharply, and the positive and negative cross-sections were relatively sharp, with more peak coefficients. After spectral contrast analysis and correlation coefficient calculation, 86 bands with higher correlation coefficient were selected for the study under the first order differential variation. On black soil airborne hyperspectral data processing, the application of partial least squares regression (PLSR) and BP neural network method respectively establish soil nutrient content of high spectral quantitative inversion model. The results showed that RPIQ values (Difference between the third and the first quartile of sample observations ratio to RMSE) of total nitrogen PLSR and BP neural network prediction model were 2.42 and 2.80, respectively. The RPIQ values of effective phosphorus PLSR and BP neural network model were 0.83 and 1.67 respectively. The RPIQ values of the available kalium PLSR and BP neural network models were 2.00 and 2.33 respectively. Experiments showed that the spectral quantitative prediction model of soil total nitrogen and available kalium has good accuracy and prediction ability. Nitrogen, phosphorus and potassium, and the spatial distribution of nutrient content in black soil were obtained. However, the prediction effect of effective Phosphorus was not particularly ideal, which could only meet the requirements of approximate quantitative prediction. At the same time, the BP neural network modeling has better accuracy and prediction ability than the partial least square modeling, and the prediction accuracy increased by 6.5%, 10.1% and 6.6% respectively. Due to the limitation of soil samples and other conditions, more samples are needed to verify the universality of the model. More data mining methods are expected to establish more robust prediction models, which will provide more reliable information for the prediction and evaluation of black soil quality information. [ABSTRACT FROM AUTHOR]

The southern area of Laizhou bay is located by the Bohai sea. There have been three seawater intrusion events in history, and a mass of high concentration saline brine has been buried in its subsurface aquifers. Large - scale exploitation of underground brine resources has been carried out since the 1970s. Brine baysalt has become a pillar industry of local economic development. In recent years, many salt pans become abandoned due to the exhaustion of regional shallow brine resources and the restriction of high cost and market factors of deep brine exploitation. In this context, some salt pans have been reclaimed based on the relevant government policies. Although a series of remediation measures that combining agriculture and engineering have been carried out on the reclaimed land of salt pans, the soil still contains a large amount of soluble salt on account of the influence of perennial baysalt process, moreover, the content of soil nutrients is also extremely low. The high soil salinity has always been the main limiting factor for the sustainable development of agriculture in the reclamation areas of abandoned salt fields. In this paper, soil sampling data of cotton growth period in four key nodes were used to study the spatial distribution characteristics of soil organic matter and soil salinity at different depths in different periods, and to analyze the correlation between them. The two-dimensional spatial distribution map of soil organic matter content and the three-dimensional spatial distribution map of soil salinity in different periods were drawn. The results showed that the variation of soil salinity and organic matter content at different depths in different periods in the study area was large, among which the maximum variation of organic matter content reached 37.3 g/kg and the maximum variation of soil salinity reached 57.2 g/kg, the variation intensity of both soil salinity and organic matter content was moderate. Soil salinity and organic matter content decreased with time change. The correlation between soil salinity and organic matter content in the soil layer of 0 - 30 cm was the highest, the range was from 0.25 to 0.38, but it did not reach the level of significant correlation. The correlation of soil salinity between different layers reached a significant or extremely significant degree. There was a moderate spatial autocorrelation between soil salinity and surface soil organic matter content. Kriging interpolation results showed that the surface soil organic matter content was distributed in a banded manner, the organic matter content increased gradually from west to east in seedling stage and flowering stage. The soil organic matter content in the flowering and boll period was the lowest in the northeast, and the highest in the harvest period was concentrated in the northwest and southeast. The three-dimensional spatial distribution of soil salinity was similar in different periods and different layers, and its spatial distribution characteristics were generally close. The high soil salinity area at seedling and flowering stage appeared in the southeast. The spatial distribution of soil salinity in flowering and flowering period was scattered and patchy. The results provide technical support for scientific improvement and rational utilization of saline soil and sustainable development of agriculture to the southern area of Laizhou Bay. [ABSTRACT FROM AUTHOR]

To evaluate reasonably the effect of reclaimed water irrigation salt in the soil environment, varying salinity in the effluent of salty solution leaching subtropical soil and the effect on soil chemical properties were analyzed. In this paper, five subtropical soils: clay fluvo aquic soil, sandy fluvo aquic soil, red soil, purple soil and paddy soil were selected as the research object. Use the constant head infiltration method to observe the differences in electrical conductivity (EC) and pH of effluent after leaching of soils with different concentrations of sodium salt solution (EC of solutions was 1.96, 4.77, 9.08, 17.25 and 25.06 dS/m, respectively). The results showed that the high concentration salt solution had weaker penetrating ability in red soil, purple soil and clay fluvo aquic soil with higher clay content than paddy soil and sandy fluvo aquic soil with low clay content. The same treatment achieved the same degree of penetration, and acidic soil (red soil, purple soil, paddy soil) can withstand more low quality water. In addition, the migration rate of salinity in the soil was mainly determined by the physicochemical properties of the soil. Soil clay content and exchangeable aluminum content significantly slowed the migration of salinity in the soil, while the soil silt content, EC, pH value and exchangeable calcium and magnesium content promoted the migration of salt in the soil. Salt can easily flow out through alkaline soil (clay fluvo aquic soil and sandy fluvo aquic soil). The maximum change rate of relative EC from the alkaline soil effluent was 36% higher than that of the acidic soil. The concentration of inflow salt had an obvious influence on the relative EC change rate and the penetration process of the red soil effluents, and it mainly affected the relative EC change rate for the purple soil, the clay fluvo aquic soil and the sandy fluvo aquic soil, which mainly affected the lag degree of the penetration process for paddy soil. The Boltzmann fitting showed the infiltration water salt concentration and soil physical and chemical properties had a significant impact on the model parameters (P<0.05). Moreover, the degree of soil chemical properties affected by the salt concentration in the infiltration solution was not only related to its own chemical properties, but also had a very significant relationship with the content of powder particles and clay in the soil texture (P<0.01). The concentration of salt solution had no significant (P > 0.05) effect on the pH value of alkaline soil, and had a greater effect on the pH value of acidic soil. The pH of the effluent decreased by 1.6-2.6 units, of which red soil had the greatest change in pH value, followed by purple soil. The influence of infiltration solution with EC higher than 4.77 dS/m on the stable pH value of soil effluent did not increase substantially. Therefore, when irrigating with low quality water, the salt concentration in the water should be sufficiently limited according to the physicochemical properties of the soil. The research results can serve as reference for reclaimed water irrigation and calculation of water and salt transport in subtropical regions. [ABSTRACT FROM AUTHOR]

In order to accurately estimate soil moisture content based on index of drought monitored in the complex type cover, this paper studied the feasibility of integrating the single index to estimate soil moisture. Wushen Banner in the abdomen of Maowusu sandy land was the study area. The annual wind velocity of this area was 3.4 m/s. The land use of this area included grassland, sandy land, forest, farmland, water body and construction land, which accounted for 55.66%, 29.3%, 10.9%, 2.75%, 0.7% and 0.69% of the total area, respectively. The remote sensing data were from Landsat 8 OLI images on August 26 and September 28 of 2016. The spatial resolution was 30 m. The data were carefully preteated. The sampling was carried out in 24 plots of 12 sandy land and 12 grassland. Traditional 3 single drought monitoring indexes were selected. The weights of each index was determined by analytic hierarchy process. Together with the measured soil moisture data from different cover types, regression analysis was applied to establish the multi-index comprehensive drought monitoring model (CDI). The accuracy of the model was validated by determination coefficient, average relative error and root mean square error (RMSE). Moreover, the spatial distribution of surface soil moisture in the studied area was inverted and analyzed based on multi-index model. The results showed that the 3 single drought indexes could objectively reflect the drought characteristics, displaying a negative correlation with surface soil moisture content. The best temperature vegetation dryness index (TVDI) correlation was 0.604. The comprehensive drought monitoring index model and multiple indexes were introduced. The determination coefficient in surface soil moisture index models for grassland and sandy land in August and September were 0.751 and 0.749, respectively. On the whole, the determination coefficient of the exponential model reached 0.744 and 0.727, respectively, which were higher than the fitting effect of a single index. With the increase of soil moisture content, the CDI value showed an obvious decreasing trend, which was ranked as sandy land higher in grassland in size. It indicated that the comprehensive drought monitoring index could better reflect soil moisture distribution in the studied area. The surface soil moisture in this area based on the model inversion was generally low, and the area with the moisture content less than 0.15 cm3/cm3 accounted for 96.47%. And most of these areas were far away from lakes and reservoirs. According to different land types and soil moisture distribution, 2 different land types such as grassland and sandy land were statistically analyzed. The results showed that the different cover types had a quite different moisture content, with an average of 0.087 cm3/cm3 for grassland in August, 0.026 cm3/cm3 for sandy land in August, 0.102 cm3/cm3for grassland in September, 0.029 cm3/cm3 for a sandy land in September. The surface characteristics of soil moisture spatial distribution for grassland was consistent with the sandy land. The accuracy verification of grassland, sandy land and the whole inversion results showed that the average relative error was less than 10%. Generally, the soil moisture content in the studied area decreased gradually from east to west and from north to south. [ABSTRACT FROM AUTHOR]

The quality of seedbed after seeding such as soil surface leveling, soil-breaking rate and seed furrow preparing and so on, are the main factors affecting the seedling rate of rapeseed. A good seedbed is a necessary condition for uniform seedling emergence, increasing the rate of subsequent seedlings and promoting the homogeneity of plants after sowing. In view of the fact that the measurement and data processing methods of rapeseed seedbed surface roughness under mechanized direct seeding cannot fully reflect the real soil surface condition, a method of measuring and quantifying roughness surface area by using laser radar scanning technology is proposed in this paper. The main components of the measuring device are the lidar, linear guide, stepper motor, portable computer and other components. The device can quickly acquire soil surface data in three dimensions through the whole working width of direct seeding machine. The surface roughness data of rapeseed combined direct seeder and no-tillage direct seeder after operation were used to detect the effect of two kinds of seedbed operation on seedbed surface. The characteristics of rapeseed direct seeding process were analyzed, three-dimensional digital modeling and detrend processing of ground data after two kinds of direct seeders were carried out by using MATLAB. The least square method was utilized to eliminate the inclined tendency of seedbed surface, the fourth order polynomial was applied to remove the slope trend in the width direction of the soil surface of rapeseed combined direct seeder. The root mean square (RMS) height and the correlation length were involved as evaluating parameters to analyze the data. Statistical results of roughness parameters for different spatial sampling intervals and different angles cross-section data showed that the average RMS height and RMS height mean error of 170 mm sampling interval were all higher than that of 5 mm sampling interval, the average RMS height of the 170 mm sampling interval was 2.2 mm higher than that of the 5 mm sampling interval, the corresponding correlation length was around 1.8 times the latter; and the RMS height and the correlation length error of the 170 mm sampling interval were higher than that of the 5 mm sampling interval. The maximum difference of RMS height and correlation length of surface elevation data were 7.69 and 25.14 mm respectively in the three directions of 0, 45 and 90 degrees in the forward direction of vertical unit, and there was obvious anisotropy on the surface of seedbed with structural characteristics such as seed trench. Statistical results of local roughness quantification using sliding sampling windows in different size regions showed that when the window width is 0.5 times the compartment width, the standard deviation of RMS height can be stabilized within 0.27 mm if the length of the window is not less than 1.2 m, and the influence of local surface tilt on the roughness calculation can be eliminated by the trend treatment of the tilt of each sampling window. The results can provide reference for the measurement and quantitative analysis of surface roughness in rape direct seeding operation. [ABSTRACT FROM AUTHOR]

In-depth studies on soil water storage in red soil slopes in south China are of important scientific significance and practical application value for flood control, drought relief and conservation of soil and water. Agricultural cultivation under the fruit forest is an important way of development and utilization of red soil slopes in southern China, and the properties of top-layer soil would be affected by biological process, soil erosion, artificial tillage, etc. Hence, it is essential to understand difference of top-layer soil hydraulic characteristics of several agroforestry systems, which may affect soil water storage. The study area lies in Jiangxi Provincial Eco-Science Park of Soil and Water Conservation (115°42′38″-115°43′06″ E、29°16′37″-29°17′40″ N), which is located in De'an County, Jiangxi Province, China and belongs to Boyang River watershed of Poyang Lake Basin. A total of 4 treatments of agroforestry systems, namely, agriculture-forestry-grass, protective farm-forest, common farm-forest, and pure forest were studied. The top layer was defined as 0-0.30 m subsurface depth in this paper, and soil samples of the top-layer soil were collected by foil sampler for each plot. For each sample, the bulk density was measured by drying method, water retention curve was test by pressure membrane meter, and saturated hydraulic conductivity was measured by saturated infiltration experiment. The van Genuchten-Mualem model was used to describe water retention curve, and the other 4soil hydraulic parameters were reciprocal of air entry pressure, grain size distribution parameter, saturated soil water content, and residual soil water content besides saturated hydraulic conductivity. The one-dimensional Richards' equation based on the Darcy's law was used to describe soil water flow due to its solid physical foundation, and the Ross method was used to solve the Richards' equation owing to the higher computational efficiency and accuracy. For the sake of simplicity, several assumptions were considered for simulation. Firstly, the difference of top-layer soil hydraulic characteristics was the only various factor of the 4 plots, and the soil profile for simulation was also divided into 2 layers, and the top layer was from soil surface to 0.30 m depth. Secondly, the simulation period was set to from August 1st to December 31st, 2010 since runoff wasn't observed in this period. Thirdly, the upper boundary condition was considered as atmospheric boundary condition, where the potential evaporation was calculated by Penman-Monteith model. Besides, the lower boundary was zero-flux boundary at 1.00 m depth where was impermeable bedrock. The statistical analysis results of soil hydraulic parameters showed the most significant difference between top and deep layer in agriculture-forestry-grass soil with the lowest viscosity and highest permeability, i.e., the largest saturated hydraulic conductivity and reciprocal of air entry pressure among the 4 plots. Correlation analysis of parameters showed that absolute of correlation coefficient between saturated hydraulic conductivity and bulk density and that between reciprocal of air entry pressure and bulk density could reach to 0.96. The distribution of soil water content of each profile was simulated, and soil water storage was calculated by the simulated soil water content. The simulation results showed the order of soil water storage under the 4 treatments from high to low as followed: agriculture-forestry-grass soil, protective farm-forest soil or common farm-forest soil and pure forest soil. The simulation results during specified periods indicted the mechanism of effects of top-layer soil hydraulic characteristics on soil water storage. For agriculture-forestry-grass soil, the top-layer soil cut off the upward movement channel of soil moisture to reduce the water consumption of the deep soil during the evaporation period, while the top-layer soil increased the downward movement to enhance the water storage of deep soil. In conclusion, agriculture-forestry-grass is worth of development and promotion in red soil slopes in south China. [ABSTRACT FROM AUTHOR]

Black soil is one of the most important cultivated land resources in Northeast China. Black soil has high soil fertility, and brings about high and stable yield. According to the survey, the humus layer of black soil is generally 30-70 cm. But black soil is on high terrain and the cultivation time is long, coupled with the neglect of enhancing soil fertility management, which lead to serious soil erosion, soil layer thinning, and soil fertility decline. Especially in the past 10 years, in order to save costs, farmers have widely used simplified technology, and the basic soil tillage method has changed from plowing to rotary tillage and stubble cleaning, which has resulted in shallow tillage layer and increased the bottom thickness. The depth of the plough bottom moves from 18-22 to 12-15 cm, and the potential productivity of black soil is restricted. People try to stop the decline of soil fertility and soil thinning by improving the application of organic fertilizer, straw returning and subsoiling technology. Our research group found that the straw deep buried and organic fertilizer application have effectively improved soil fertility. In view of removing the obstacle of continuous cropping, the existing technologies including the nutritional therapy, soil disinfection, and crop rotation technology had the problem of high cost and were difficult in the rotation of crops. Therefore, these techniques were limited to solve the problem of soil continuous cropping obstacles. According to the principle of land fallow for leisure, the technology of improving soil by stereo leisure was presented in this paper, which was aimed at continuous cropping obstacles in soils. Through making full use of the characteristics of black soil with deep humus layer, continuous cropping soil was regularly turned to lower leisure. By alternate use of upper and lower soil, the objectives of soil leisure and agricultural sustainable development would be achieved. In this paper, a machine developed to turn the top soil to the lower layer was operated in the black soil field for breaking its hard plough pan. As the depth of top black soil is more than 40 cm, it has good homogeneity from up part to low part, which can provide a choice for developing soil layer up-down fallow technology. Two test fields were selected. One was operated by above mentioned machine, and the other was operated by conventional machine. The results showed that in the up-down fallow field the soil bulk density was decreased by 0.05, 0.11 g/cm3 respectively compared with that in the conventional field. The soil aeration coefficient was increased by 14.97×10-2, 16.69×10-2 cm/s respectively in the first year and second year. The soil saturated hydraulic conductivity was reduced by 3.14×10-3 in the first year, increased by 10.95×10-3 cm/s in the second year. The soil shearing strength was reduced by 0.72 in the first year, increased by 0.82 kPa in the second year, and the soil moisture content was increased by 4.07%, 4.95% respectively in the first year and second year. It was also found that in the up-down fallow field, soil chemical index including soil organic matter, alkali-hydrolysable nitrogen, available phosphorus and available potassium tended to be lower in the upper layer but higher in the down layer. Under the rotation conditions, the yield of potato and beet in the up-down fallow field was decreased by 5.63% and 3.06% respectively in the first year, but the yield of corn and potato increased by 5.20% and 27.00% respectively in the second year. Under the soybean continuous cropping conditions, soybean grew well in the up-down fallow field, dry weight and root dry weight of soybean were increased by 7.63%-7.82% and 7.61%-13.41% respectively, root length was increased by 4.42%-6.26%, pod number and grain number per plant were increased by 18.83%-20.71% and 32.43%-37.21% respectively, and nodule number was increased by 1.46-5.15. During the 2 tested years, soybean yield in the up-down fallow field was 3.09%-22.38% higher than that in the conventional field. [ABSTRACT FROM AUTHOR]

Digging machine is a kind of digging and tillage machine. Because its structure is simple and it can be operated conveniently, it is widely used as a hole digger. There are mainly 4 types of digging machines, i.e. suspension type, portable type, traction type and self-propelled type. On the mountains, hills, ravines and other complex terrain conditions, portable type of digging machine is popularly used to dig a hole so as to plant or transplant trees. Hence, this paper designed a new portable digging machine with a half-nut mechanism to keep the feed rate stable and decrease the torque of the drilling bit as far as possible when drilling the hole. In addition, the support structure was also designed for the digging machine for the sake of guaranteeing the verticality of the hole and ensuring the reliability and stability of the digging machine, as well as making the structure more secure. The feed rate of the digging machine was an important factor, which affected the torque and work efficiency of the drilling bit greatly. Research on the effect of the feed rate on the dynamic mechanical parameters of digging machine was of great significance for developing a new model of digging machine. However, the power of the digging machine was gasoline engine, so the power output shaft could not reversely rotate, and it could not be used for actual digging. Thus there was a great need to design a new structure that could solve the gasoline engine's problem of rotating only in one direction. Accordingly, the half-nut mechanism was designed. According to the working principle of the half-nut, the motion characteristics of half-nut mechanism were analyzed by using the analytic method. The straight track angle of half-nut picks was decided as 105°, and thus a portable digging machine with half-nut mechanism was designed. The new designed digging machine could not only realize the digging operation automatically, but also complete the return movement rapidly. Then based on the working principle of digging machine, the relationship between the feed rate and the effect of lifting soil was studied. In order to verify the result, the experiment of testing the torque and rotational speed during the process of drilling a hole was conducted by using the torque measuring device JN338-100A made by Beijing Xinyuhang Century Science and Technology Co., Ltd. to collect the data afterward. Therefore it successfully provided a theoretical basis for the determination of feed rate of a new type of digging machine. It showed that when the pitch of half nut was taken as 3 or 5 mm, the torque and its fluctuation both were small. However when the pitch of half nut was taken as 8 mm, for it did not satisfy the working principle of digging machine, the torque and its fluctuation varied greatly, and the digging machine could not lift soil smoothly. In order to improve the work efficiency, the pitch of half nut was taken as 5 mm for this new designed digging mechanism finally. This paper provides a theoretical basis for the design of automatic feed mechanism of a new portable digging machine. [ABSTRACT FROM AUTHOR]

The spatial variability of soil organic carbon (SOC) is one of the reasons leading to uncertainty in the estimation of carbon stocks. Simulation and analysis research of SOC spatial distribution, especially the three-dimensional (3D) spatial distribution characteristics, is of great significance for revealing the soil nutrient and pollutant migration, the precise management of farmland and agricultural sustainable development. The 3D spatial distribution pattern of SOC was estimated using 3D ordinary Kriging with regard to the isotropy (3DOKI), 3D ordinary Kriging and 3D CoKriging coupling Markov with regard to anisotropy (3DOKA and 3DCKMA) in the region. Based on estimation results, the paper revealed 3D distribution pattern of regional SOC content. The mean root mean square error (RMSE), relative improvement (RI), the scatter diagram of SOC simulated and measured value and specific value coverage ratio were used to estimate the accuracy of different approaches, and the mean squared deviation ratio (MSDR) and the 3D variogram were used to evaluate model fitting effect and spatial local uncertainty. The results showed that 3D spatial distribution patterns of SOC content for the 3 kinds of estimation methods were basically the same, and the overall spatial distribution pattern was SOC content of the west and the north was higher, and that of the east and the south was relatively low. SOC contents of 5 layers (0-20, >20-40, >40-60, >60-80 and >80-100 cm) were 11.88±5.76, 10.08±4.89, 8.40±5.49, 7.83±5.89 and 7.17±5.22 g/kg, respectively. With the increase of soil depth, the SOC content of the patch gradually reduced. No matter which kind of method, the spatial distribution of SOC in different soil depth was similar, that was, the distribution characteristics of surface layer of the patch were also the embodiment of the deep soil layer. Compared to 3DOKI, the spatial search strategy and its parameters with regard to anisotropy were able to reduce defect (Bovine and central tendency effect) of Kriging method in a certain extent. The RMSE values for 3DOKI, 3DOKA and 3DCKMA were 3.1645, 2.0523 and 1.6215, respectively, so the RMSE value was the minimum for 3DCKAM, whose RI reached nearly 50%. Specific value coverage ratio for 3DOKI, 3DOKA and 3DCKMA were 33.12%, 57.83% and 76.15%, respectively, which was the largest for 3DCKMA method, whose MSDR value (1.4409) was the most close to 1, and variance was the least. The same position CoKriging method coupling Markov was more accurate, and its model fitting effect was the best, and uncertainty was the smallest, which could better highlight the volatility and reflect the specific value. The related research results of this paper will provide method reference for the regional soil properties, and provide technical guidance for the reasonable and scientific research of the spatial distribution pattern of regional SOC. [ABSTRACT FROM AUTHOR]

Cultivated land resource is the material base that mankind depend on for existence. Understanding how the cultivated land changes in quantity and quality has an important significance for country's food security and social stability. Based on the satellite images from Landsat TM/ETM in 2000 and OLI in 2013, this paper mapped the spatial distribution of cultivated land in the midwest Jilin province both in 2000 and 2013 and analyzed its temporal and spatial changes. Furthermore, soil data from 2351 field sampling points in study area were used to evaluate the quality of cultivated land and a comprehensive evaluation was made. Results revealed that cultivated land area in the midwest Jilin province increased from 5.61×104 km2 in 2000 to 5.64×104 km2 in 2013, among which dry farmland increased by 645 km2 and paddy field decreased by 350 km2.The transformation between dry land and paddy land was evident.Distribution of cultivated land changed differently from the east to the west:increasing in west part of study area and decreasing in east part, which resulted in the gravity center of cultivated land moved toward the west obviously. The increased cultivated lands were mainly converted from wetland and grassland, accounting for 66.04% and 21.12% of the total change area, respectively. The lost cultivated lands were mainly turned to artificial area, woodland and wetland with an area percent of 45.08%, 28.85% and 22.61%, respectively (mainly distributed around Changchun city). In terms of cultivated land quality, most cultivated lands were in uppermiddle grade in the midwest Jilin province in 2013, and the quality in the east part was better than that of the west.Although the total area of cultivated land increased, the quality of increased cultivated land mainly distributing in Baicheng and Songyuan city corresponded to lower grades including the third, fourth and fifth class with an area of 235,8 and 218 km2 respectively. Besides, the area of cultivated land in first class decreased by 305 km2, which mostly happened in the surrounding regions of Changchun city. The factors influencing the change of cultivated land were analyzed and we found that urbanization and policy were the most important driving forces to affect cultivated land quality and quantity. Accompanied by the rapid urbanization process, more and more highquality cultivated lands were occupied. Newly increased cultivated lands were mostly reclaimed from salinized land, alkalized land and wasteland, which led to an increase of cultivated land area and a decrease in quality. Overall, the cultivated land in the midwest Jilin province degraded severely during the past 15 years. This paper can provide an important reference for regional sustainable development of cultivated land resource. [ABSTRACT FROM AUTHOR]

The quality of seedbed after seeding such as soil surface leveling, soil-breaking rate and seed furrow preparing and so on, are the main factors affecting the seedling rate of rapeseed. A good seedbed is a necessary condition for uniform seedling emergence, increasing the rate of subsequent seedlings and promoting the homogeneity of plants after sowing. In view of the fact that the measurement and data processing methods of rapeseed seedbed surface roughness under mechanized direct seeding cannot fully reflect the real soil surface condition, a method of measuring and quantifying roughness surface area by using laser radar scanning technology is proposed in this paper. The main components of the measuring device are the lidar, linear guide, stepper motor, portable computer and other components. The device can quickly acquire soil surface data in three dimensions through the whole working width of direct seeding machine. The surface roughness data of rapeseed combined direct seeder and no-tillage direct seeder after operation were used to detect the effect of two kinds of seedbed operation on seedbed surface. The characteristics of rapeseed direct seeding process were analyzed, three-dimensional digital modeling and detrend processing of ground data after two kinds of direct seeders were carried out by using MATLAB. The least square method was utilized to eliminate the inclined tendency of seedbed surface, the fourth order polynomial was applied to remove the slope trend in the width direction of the soil surface of rapeseed combined direct seeder. The root mean square (RMS) height and the correlation length were involved as evaluating parameters to analyze the data. Statistical results of roughness parameters for different spatial sampling intervals and different angles cross-section data showed that the average RMS height and RMS height mean error of 170 mm sampling interval were all higher than that of 5 mm sampling interval, the average RMS height of the 170 mm sampling interval was 2.2 mm higher than that of the 5 mm sampling interval, the corresponding correlation length was around 1.8 times the latter; and the RMS height and the correlation length error of the 170 mm sampling interval were higher than that of the 5 mm sampling interval. The maximum difference of RMS height and correlation length of surface elevation data were 7.69 and 25.14 mm respectively in the three directions of 0, 45 and 90 degrees in the forward direction of vertical unit, and there was obvious anisotropy on the surface of seedbed with structural characteristics such as seed trench. The maximum difference of RMS height and correlation length in different directions were 7.69 and 25.14 mm, respectively. Statistical results of local roughness quantification using sliding sampling windows in different size regions showed that when the window width is 0.5 times the compartment width, the standard deviation of RMS height can be stabilized within 0.27 mm if the length of the window is not less than 1.2 m, and the influence of local surface tilt on the roughness calculation can be eliminated by the trend treatment of the tilt of each sampling window. The results can provide reference for the measurement and quantitative analysis of surface roughness in rape direct seeding operation. [ABSTRACT FROM AUTHOR]

In-depth studies on soil water storage in red soil slopes in south China are of important scientific significance and practical application value for flood control, drought relief and conservation of soil and water. Agricultural cultivation under the fruit forest is an important way of development and utilization of red soil slopes in southern China, and the properties of top-layer soil would be affected by biological process, soil erosion, artificial tillage, etc. Hence, it is essential to understand difference of top-layer soil hydraulic characteristics of several agroforestry systems, which may affect soil water storage. The study area lies in Jiangxi Provincial Eco-Science Park of Soil and Water Conservation (115°42′38″-115°43′06″ E、 29°16′37″-29°17′40″ N), which is located in De’an County, Jiangxi Province, China and belongs to Boyang River watershed of Poyang Lake Basin. A total of 4 treatments of agroforestry systems, namely, agriculture-forestry-grass, protective farm-forest, common farm-forest, and pure forest were studied. The top layer was defined as 0-0.30 m subsurface depth in this paper, and soil samples of the top-layer soil were collected by foil sampler for each plot. For each sample, the bulk density was measured by drying method, water retention curve was test by pressure membrane meter, and saturated hydraulic conductivity was measured by saturated infiltration experiment. The van Genuchten-Mualem model was used to describe water retention curve, and the other 4soil hydraulic parameters were reciprocal of air entry pressure, grain size distribution parameter, saturated soil water content, and residual soil water content besides saturated hydraulic conductivity. The one-dimensional Richards’ equation based on the Darcy’s law was used to describe soil water flow due to its solid physical foundation, and the Ross method was used to solve the Richards’ equation owing to the higher computational efficiency and accuracy. For the sake of simplicity, several assumptions were considered for simulation. Firstly, the difference of top-layer soil hydraulic characteristics was the only various factor of the 4 plots, and the soil profile for simulation was also divided into 2 layers, and the top layer was from soil surface to 0.30 m depth. Secondly, the simulation period was set to from August 1st to December 31st, 2010 since runoff wasn’t observed in this period. Thirdly, the upper boundary condition was considered as atmospheric boundary condition, where the potential evaporation was calculated by Penman-Monteith model. Besides, the lower boundary was zero-flux boundary at 1.00 m depth where was impermeable bedrock. The statistical analysis results of soil hydraulic parameters showed the most significant difference between top and deep layer in agriculture-forestry-grass soil with the lowest viscosity and highest permeability, i.e., the largest saturated hydraulic conductivity and reciprocal of air entry pressure among the 4 plots. Correlation analysis of parameters showed that both correlation coefficient between saturated hydraulic conductivity and bulk density and that between reciprocal of air entry pressure and bulk density could reach to 0.96. The distribution of soil water content of each profile was simulated, and soil water storage was calculated by the simulated soil water content. The simulation results showed the order of soil water storage under the 4 treatments from high to low as followed: agriculture-forestry-grass soil, protective farm-forest soil or common farm-forest soil and pure forest soil. The simulation results during specified periods indicted the mechanism of effects of top-layer soil hydraulic characteristics on soil water storage. For agriculture-forestry-grass soil, the top-layer soil cut off the upward movement channel of soil moisture to reduce the water consumption of the deep soil during the evaporation period, while the top-layer soil increased the downward movement to enhance the water storage of deep soil. In conclusion, agriculture-forestry-grass is worth of development and promotion in red soil slopes in south China. [ABSTRACT FROM AUTHOR]

Most studies on rills are conducted under simulated rainfall condition. However, the study under natural rainfall condition is rare, especially under extreme storm condition. In this study, we investigated rill erosion under the rainstorm that occurred on 26 July, in Zizhou County, Shaanxi Province. The 16 investigation sites were in Qingshuigou small watershed involving 5 slope surfaces of slope farmland, including 3 straight slopes, 1 convex slope, and 1 shallow ditch terrain slope. For each investigation point, the size of the quadrats was set as 2 m×2 m, and 2-3 duplicates were set. Rill intensity, rill density and degree of rill dissection of each sample plot were measured to discuss the influence of slope position (distance from watershed), slope gradient and slope type on rill characteristics of slope farmland. The results showed that: rill erosion intensity, rill density and degree of rill dissection were 2 289-110 976 t/km2, 0.3-3.95 m/m2 and 0.002-0.441, respectively. The width of rills varied from 0.5 to 60 cm, with 51% rills ranging from 10 to 15 cm in width, and 93% rills was less than 20cm. The depth of the rill varied from 0.5 to 35 cm, with 69% of rills ranging from 0 to 5 cm, and 97% of the rill depth was less than 15cm. As the increase of distance from the watershed, rill erosion intensity increased, and rill erosion developed rapidly firstly and then slowed down. Between 17-58 m from the watershed, with the increase of distance, rills developed rapidly and the degree of fragmentation of the slope increased. After 58 m from the watershed, the development of rills slowed down and the degree of fragmentation of the slope weakened. The effect of slope gradient on the rill erosion varied among different slope positions. With the increase of slope gradient, in the upper part of the slope (20-40 m from the watershed), rill erosion intensity raised sharply, and slope fragmentation degree increased. With the increase of slope gradient, in the lower part of the slope (60-80 m from the watershed), rill erosion intensity increased slowly, and slope fragmentation degree weakened. In convex slope, the middle slope had the largest rill erosion intensity (10 292 t/km2), followed by the lower slope (8 141 t/km2) and the upper slope (no rill erosion but have surface erosion). With increase of the distance from watershed, rill density, degree of rill dissection and rill depth increased firstly and then decreased, while rill erosion intensity and rill depth increased. In the slope with shallow gully, the rill erosion of sloping farmland and abandoned farmland increased with the increase of the distance. However, the existence of abandoned farmland weakened the development of rill. In the straight slope, rill developed rapidly due to the larger slope gradient. Therefore， the straight slope had the largest rill erosion intensity, rill density and degree of rill dissection in the three slope types. This paper analyzes the erosion status and regularity of rills in slope farmland during this rainstorm, and discusses the influence of slope position, slope gradient and slope shape on rill erosion of slope surface, aim to provide reference for soil erosion control of sloping farmland on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Straw returning to the filed can not only improve soil fertility, but also alleviate the imbalance of nitrogen, phosphorus and potassium, improve crop yield and quality, and reduce the cost of agricultural production. Rice straw is decomposed gradually by microorganisms in the soil, which can release nitrogen to the soil for rice growth. Nitrogen released from straw can be divided into expended nitrogen and nitrogen retained in soil. Expended nitrogen can be further divided into nitrogen absorbed by plant and lost nitrogen. 15N tracer technology is an effective means to study the nitrogen budget of farmland, by which we can accurately grasp the status of nitrogen utilization and residue, and analyze the nitrogen utilization efficiency of straw. Understanding the utilization rate of straw nitrogen is the premise of fertilization regulation and control. Heilongjiang Province still lacks the utilization rate of nitrogen in rice straw and the technical achievements of nitrogen regulation and control under straw returning conditions. In this paper, we take Qianjin Farm(132°17′E,47°34′N), Sanjiang Plain as test site and the albic soil as the test soil. we conduct a series of experiments during nitrogen regulation and control period including 15N straw labeling tracer test and straw returning nitrogen optimization test, the utilization rate of nitrogen in straw after rice straw returns to the albic soil is defined and the optimized application technology of nitrogen fertilizer after rice straw returns to the albic soil is summarized, so as to provide theoretical basis and technical guidance for optimized application of nitrogen fertilizer after straw returns to the field. The results showed that, according to 15N isotope tracer, the contribution rate of straw nitrogen in the albic soil to rice plant nitrogen accumulation was 6.49%~7.48%, 3.26%~4.16% to stem and leaf nitrogen accumulation, 8.67%~9.74% to seed; the total nitrogen use efficiency of straw was 6.51%~7.65% in the current year, and the adjustment of C/N ratio was beneficial to improving straw nitrogen utilization rate. Field experiments showed that the nitrogen application rate under straw returning was 10% lower than that under conventional nitrogen application for three consecutive years, and the field with good drainage had the effect of increasing yield, with the average yield increase by 6.17% for three years, and the yield with the reduction of nitrogen by more than 20% was low and unstable. Balanced and basal nitrogen reduction was suitable in nitrogen reduction period, and the yield was reduced significantly in case of fertilizer for tillering and panicle with nitrogen reduction; the field with poor drainage was not suitable for nitrogen reduction, otherwise, it led to yield reduction. There are differences in nitrogen regulation and control after straw returns to different kinds of soil. The corresponding measures for nitrogen management should be formulated according to soil conditions. [ABSTRACT FROM AUTHOR]

This paper was aimed to investigate the effects of organic fertilizer application (single application of organic fertilizer and organic-inorganic fertilizer combination) on the CO2 emission in farmland soil during crop growth period, under different climate types, fertilization measures, organic fertilizer types and experiment years in Northern China. Non-fertilizer and inorganic fertilizer application were used as control treatments. Based on the published data of relevant experiment and the Meta-analysis method, the quantitative effects on application of organic fertilizer and organic-inorganic fertilizer combination on CO2 emission in farmland soil were studied. A total of 534 measurements were obtained including 89 pairs of data from 21 literatures. The experiments lasted from 1980 to 2017. The effects were determined by effect size by Meta-analysis method. The important factors affecting CO2 emission were selected by finding out those with important values higher than 0.8. The results showed that the organic fertilizer application significantly generally increased the CO2 emission in farmland soil than the non-fertilizer and inorganic fertilizer application, with an increment of 50.6% and 36.3%, respectively. No publication bias was found because the fail-safe number was far higher than the critical values by the fail-safe method. There was not significantly different among regions (P>0.05). Under the application of organic fertilizer, the CO2 emission of farmland soil decreased successively in the following order: single application of organic fertilizer, organic-inorganic fertilizer combination, and combined application of inorganic fertilizer, organic fertilizer and slow-release fertilizer. Soil CO2 emission did not significantly increase under the combined application of organic fertilizer, inorganic fertilizer and slow-release fertilizer. Compared with non-fertilizer, cow manure, pig manure and commercial organic manure, chicken manure had the greatest positive effects on soil CO2 emission. Under the application of organic fertilizer, the CO2 emission of farmland soil in gray desert was relatively high. The CO2 emission of farmland soil was positively correlated with the annual average temperature and negatively correlated with the annual average precipitation. The annual average temperature and annual average precipitation could explain about 11%-16% and 10%-12% change in effect size of CO2 emission, respectively. From the perspective of environment, it was suggested to apply the combined application of inorganic fertilizer, organic fertilizer and slow-release fertilizer in Northern China. Meanwhile, the chicken manure should not be applied in large quantities and organic fertilizer should not be used in grey desert farmland. The results of this study can provide valuable information for the popularization and application of organic fertilizer replacing partial chemical fertilizer in Northern China. [ABSTRACT FROM AUTHOR]

In order to solve the problems of high resistance and high power consumption of rotary tillage and land preparation, the rotary blade is studied based on theoretical analysis, simulation and field experiment in this paper. First, a wedge drag reduction rotary blade is designed based on the theoretical force model of cutting tools in mechanical soil dynamics. Second , the three-dimensional model of the national rotary blade and the wedge drag reduction rotary blade is established by using the Inventor software and the simulation experiment is carried on. The cutting soil model of 2 kinds of rotary blades is established by using HyperMesh software, and the material parameters, boundary constraints and working parameters are defined. On this basis, the soil cutting process, stress and cutting resistance are analyzed. It is proved that the wedge drag reduction rotary blade design is reasonable. In order to verify whether the wedge drag reduction rotary blade meets the strength requirement, the stress of the rotary blades is analyzed, and the cutting resistance of the national rotary blade and the wedge drag reduction rotary blade are compared. Third, field comparative experiments are carried out on national rotary blade and wedge drag reducing rotating blade with the evaluation indexes of torque, power consumption and soil breakage. The results show that the cutting resistance of the wedge drag reduction rotary blade is smaller than that of the national rotary blade; the maximum stress of the national rotary blade is 35.68 MPa and the maximum stress of the wedge drag reduction rotary blade is 29.49 MPa, which is less than that of the national rotary blade and far less than the yield strength of the material 430 MPa. On the premise of ensuring the strength of the blade body, the weight of the wedge drag reduction rotary blade is reduced by about 50 g, which is about 8.3% lower than that of the national rotary blade. The maximum cutting resistance of the national rotary blade is 530 N, the average cutting resistance is 375.5 N, and the maximum cutting resistance of the wedge drag reduction rotary blade is 510 N, the average cutting resistance is 335.5 N, the average cutting resistance of the wedge drag reduction rotary blade is 10.65% lower than that of the national rotary blade, which proves the feasibility of the wedge drag reduction rotary blade designed; The average torque of the wedge drag reduction rotary blade is 11.35% lower than that of the national rotary blade. In the working process of rotary blades, the average power consumption of the national rotary blade is 74.2 kW, the average power consumption of the wedge drag reduction rotary blade is 67.3 kW, and the average power consumption of the wedge drag reduction rotary blade is 9.29% lower than that of the national rotary blade. The average breaking rate of soil of the national rotary blade is 75%, and the average breaking rate of wedge drag reduction rotary blade is 79%, which is 4% higher than that of the national rotary blade; After continuous 33 hm2 tillage, rotary blades did not break, and the average wear of the national rotary blade is 98.5 g, the average wear of the wedge shaped drag reduction rotary blade is 97.3 g, the wear difference is 1.3%, and the wear degree is the same. The wedge drag reduction rotary blade can effectively solve the problems of high resistance and high power consumption of rotary blade, which is helpful to accelerate the development of arable land machinery, improve the mechanization level of cultivated land, and reduce the production cost of crops. [ABSTRACT FROM AUTHOR]

In recent years, intensive and extensive farm managements have resulted in a decline in the quality of cultivated land. Excessive inputs have been leached from farmland to rivers and lakes, especially the leaching of nutrients, heavy metals and pesticide residues, which has aggravated the risk of pollution to agricultural environment. As a critical methodology of agricultural environment monitoring, the lysimeter has been applied to monitor the characteristics of soil leaching components, to simulate the migration of soil water and nutrients, and to assess the effects of farm managements on agricultural ecosystems, eventually to provide technical assistance for scientists to make a better management decision in the farmland ecosystem. In this paper, the methods of construction, layout, soil filling, soil surface isolation and sampling in the main types of lysimeters monitoring system were summarized. Based on that, the merits and shortcomings of different types of lysimeters were analyzed, and the main factors affecting the monitoring results of lysimeter were discussed. In the end, suggestions and prospects were put forward based on the current situation of lysimeter in agricultural environment monitoring. Overall, for the rectangular concrete lysimeter, the biggest advantage is that cost of construction and operation and requirements for technology is relatively low, however, large quantities of soil excavation, concrete construction and soil back filling are always time-consuming and usually cause high soil disturbance and significant artificial effect and need to undergo a transition period. Besides that, the problem of infiltration from inside to outside at the bottom and side of concrete lysimeter also needs to be overcome. Conversely, for barrel or vessel lysimeter, the monolith soil usually undergoes minimal disturbance by extracting and filling the cylindrical blocks, the process is much more simple, which can be achieved just by mechanical equipment including cutting system, crane, trucks and so on. It takes shorter time compared to concrete lysimeter, the whole procedure of obtaining monolith soil just takes one day or more and can be put into use immediately without transition period. Consequently the soil conditions are more comparable to natural field conditions and data could be accurately detected and collected. However, the technological and equipment requirements of monolith soil extraction, filling and transportation are relative high, as well as the cost of construction and operation. Besides that, boundary effect is much more significant compared to the concrete lysimeter due to the minimal soil base area. The artificial effect and boundary effect cannot be eliminated completely at the same time in the semi-closed lysimeter system, the selection and construction of lysimeter system should be depended on specific research needs, local geological and topographic conditions and their own technology level. Therefore, a more practical strategy need to be taken into consideration, that is to build a more suitable lysimeter within the acceptable deviation range and the given budget, being able to implement higher data accuracy with lower costs. Finally, building and running a long-term lysimeter station with continuously improved technologies, joining a platform, sharing methods, data and models, and constructing a network of lysimeter system are also recommended. [ABSTRACT FROM AUTHOR]

Sloping farmland is an important part of cultivated land resources in Yunnan district. The evaluation of cultivated-layer soil quality and the appropriate range of parameters for sloping farmland are the basis for the development of reasonable plough layer. Based on the Soil Management Assessment Framework (SMAF), taking the cultivated-layer soil quality of sloping farmland in Yunnan province as the research object, this paper constructed a soil quality index evaluation model (CLSQI) for sloping farmland, and used the minimum data set (MDS) method to screen the evaluation indicators to evaluate the soil quality of sloping farmland in Yunnan, proposed the range of soil parameters for rational tillage in sloping farmland. The results showed that the minimum data set (MDS) of soil quality evaluation of sloping farmland in Yunnan region consisted of five indicators: pH value, total nitrogen, total porosity, soil shear strength and slope. The comparative analysis of AL-CLSQI (the cultivated-layer soil quality index calculated by all indicators) and AL-CLSQI (the cultivated-layer soil quality index calculated by the minimum data set index) showed that the evaluation accuracy of cultivated-layer soil quality based on MDS index was higher. In the primary selection index system, the weights of soil bulk density, total porosity, capillary porosity, shear strength, and slope grade were larger, while in the MDS index system, the weight of the slope and total nitrogen content was larger. The cultivated-layer soil quality index (CLSQI) of sloping cultivated land was between 0.39 and 0.84, the mean value was 0.59±0.11, and the coefficient of variation was 0.19. The cultivated-layer soil quality of sloping farmland was generally “medium”, and it was generally low. The CLSQI of the sloping farmland in different sampling areas was significantly different (P<0.05), and the size relationship was: Chuxiong＞Shuangbai＞Xuanwei＞Ninger＞Malong＞ Shilin. The 0～20 cm sampling depth sloping farmland CLSQI (mean value 0.59) was greater than >20 cm (mean value 0.56), and the CLSQI (mean value 0.61) of purple soil sloping farmland was larger than the red soil (mean value 0.54) (P<0.05), while the ridge and contour farming cultivation mode sloping farmland CLSQI was larger than that of the straight-plowing. The order of the CLSQI of the sloping farmland in different agricultural divisions was: Northeastern Yunnan＞Central Yunnan ＞Southwest Yunnan. According to the corresponding relationship between the soil quality of the cultivated-layer and the crop productivity and membership function, the cultivated-layer was in a relatively reasonable state when the soil quality grade of the sloping farmland was at a “higher” and above level (CLSQI≥0.6). The appropriate range of MDS indicators for cultivated-layer of sloping land in Yunnan were indicated as follows: the pH value of 5.58～7.82, the total nitrogen content of ≥1.37 g/kg, the total porosity content of ≥52.28%, the soil shear strength value of ≥5.19 kPa, and slope value of ≤11.79°. The suitable range of the above-mentioned cultivated-layer soil parameters can be used as the standard for the rational cultivated-layer diagnosis of sloping farmland in Yunnan. The research can provide theoretical basis and parameter support for the quality evaluation of ploughed plough layer and the construction of reasonable plough layer. [ABSTRACT FROM AUTHOR]

Cracks are common in nature and affect a number of soil properties. They increase the permeability, reduce the soil strength and stability, and thus affect the growth of plant roots. This paper presented a model for crack formation which was introducing the correlation length to constructing the soil critical strain random field to optimize the cracking model. The model was based on a lattice of Hookean springs with finite strength and the critical strain. The concept of correlation length was introduced to constructs the critical strain random field, the correlation length was used for reflects the spatial continuity of the soil. The critical strain random fields were generated using program written by Fortran language. The model reproduced the dynamics characteristic of the development of crack network in nature, and some of the parameters of the model represented the physical properties of the soil. We processed the digital images to quantitatively analyze the geometric characteristics of cracks. The typical procedure of digital image processing included: the color image of the crack patterns was converted into a gray one, the gray image was further changed into a binary one with the threshold division method. After the process, the cracks and aggregates were simply distinguished in a black-white image, in which the black lines and the white areas represent the crack networks and the aggregates, respectively. We optimized the threshold to make the binary images as clear as possible, and processed the images through binarization, noise removal and edge extraction of crack for extraction of morphological properties. Finally, the influence on model simulation cracking of spatial correlation length, heterogeneity in random field was analyzed. Comparison of crack area, crack length, Euler number density by calculating experiment and simulation images, it could be drawn that crack morphology could be described by Minkowski area, length, Euler number density effectively. By calculating the average μ, standard deviation δ of cracks area, length, Euler number density, the images of average density value μ and μ±δ are basically the same in the change trend between experimental and simulated process. After calculation, the coefficients of determination R2 for the area, length and Euler number density are all larger than 0.5, and the root mean square error and deviation are small enough. The consistency index IA quite approach to 1, which indicating that the calibration results are satisfactory. The two models are compared, among them the determination coefficient R2 is between 0.889-0.968, the consistency index IA is between 0.964-0.993, which reflecting the dynamic cracking process of cracks well. The greater the correlation length and the smaller the variance, the lower the discretization degree of the random field, that the more uniform the soil cracking. On the contrary, there are mainly isolated cracks. And the mean value is too small, the whole strain of the random field is low, the simulated crack does not consistent with the development of the natural crack. [ABSTRACT FROM AUTHOR]

To evaluate reasonably the effect of reclaimed water irrigation salt in the soil environment, varying salinity in the effluent of salty solution leaching subtropical soil and the effect on soil chemical properties were analyzed. In this paper, five subtropical soils: clay fluvo aquic soil, sandy fluvo aquic soil, red soil, purple soil and paddy soil were selected as the research object. Use the constant head infiltration method to observe the differences in electrical conductivity (EC) and pH of effluent after leaching of soils with different concentrations of sodium salt solution (EC of solutions was 1.96, 4.77, 9.08, 17.25 and 25.06 dS/m, respectively). The results showed that the high concentration salt solution had weaker penetrating ability in red soil, purple soil and clay fluvo aquic soil with higher clay content than paddy soil and sandy fluvo aquic soil with low clay content. The same treatment achieved the same degree of penetration, and acidic soil (red soil, purple soil, paddy soil) can withstand more low quality water. In addition, the migration rate of salinity in the soil was mainly determined by the physicochemical properties of the soil. Soil clay content and exchangeable aluminum content significantly slowed the migration of salinity in the soil, while the soil silt content, EC, pH value and exchangeable calcium and magnesium content promoted the migration of salt in the soil. Salt can easily flow out through alkaline soil (clay fluvo aquic soil and sandy fluvo aquic soil). The maximum change rate of relative EC from the alkaline soil effluent was 36% higher than that of the acidic soil. The concentration of inflow salt had an obvious influence on the relative EC change rate and the penetration process of the red soil effluents, and it mainly affected the relative EC change rate for the purple soil, the clay fluvo aquic soil and the sandy fluvo aquic soil, which mainly affected the lag degree of the penetration process for paddy soil. The Boltzmann fitting showed the infiltration water salt concentration and soil physical and chemical properties had a significant impact on the model parameters (P<0.05). Moreover, the degree of soil chemical properties affected by the salt concentration in the infiltration solution was not only related to its own chemical properties, but also had a very significant relationship with the content of powder particles and clay in the soil texture (P<0.01). The concentration of salt solution had no significant (P > 0.05) effect on the pH value of alkaline soil, and had a greater effect on the pH value of acidic soil. The pH of the effluent decreased by 1.6-2.6 units, of which red soil had the greatest change in pH value, followed by purple soil. The influence of infiltration solution with EC higher than 4.77 dS/m on the stable pH value of soil effluent did not increase substantially. Therefore, when irrigating with low quality water, the salt concentration in the water should be sufficiently limited according to the physicochemical properties of the soil. The research results can serve as reference for reclaimed water irrigation and calculation of water and salt transport in subtropical regions [ABSTRACT FROM AUTHOR]

To evaluate reasonably the effect of reclaimed water irrigation salt in the soil environment, varying salinity in the effluent of salty solution leaching subtropical soil and the effect on soil chemical properties were analyzed. In this paper, five subtropical soils: clay fluvo aquic soil, sandy fluvo aquic soil, red soil, purple soil and paddy soil were selected as the research object. Use the constant head infiltration method to observe the differences in electrical conductivity (EC) and pH of effluent after leaching of soils with different concentrations of sodium salt solution (EC of solutions was 1.96, 4.77, 9.08, 17.25 and 25.06 dS/m, respectively). The results showed that the high concentration salt solution had weaker penetrating ability in red soil, purple soil and clay fluvo aquic soil with higher clay content than paddy soil and sandy fluvo aquic soil with low clay content. The same treatment achieved the same degree of penetration, and acidic soil (red soil, purple soil, paddy soil) can withstand more low quality water. In addition, the migration rate of salinity in the soil was mainly determined by the physicochemical properties of the soil. Soil clay content and exchangeable aluminum content significantly slowed the migration of salinity in the soil, while the soil silt content, EC, pH value and exchangeable calcium and magnesium content promoted the migration of salt in the soil. Salt can easily flow out through alkaline soil (clay fluvo aquic soil and sandy fluvo aquic soil). The maximum change rate of relative EC from the alkaline soil effluent was 36% higher than that of the acidic soil. The concentration of inflow salt had an obvious influence on the relative EC change rate and the penetration process of the red soil effluents, and it mainly affected the relative EC change rate for the purple soil, the clay fluvo aquic soil and the sandy fluvo aquic soil, which mainly affected the lag degree of the penetration process for paddy soil. The Boltzmann fitting showed the infiltration water salt concentration and soil physical and chemical properties had a significant impact on the model parameters (P<0.05). Moreover, the degree of soil chemical properties affected by the salt concentration in the infiltration solution was not only related to its own chemical properties, but also had a very significant relationship with the content of powder particles and clay in the soil texture (P<0.01). The concentration of salt solution had no significant (P > 0.05) effect on the pH value of alkaline soil, and had a greater effect on the pH value of acidic soil. The pH of the effluent decreased by 1.6-2.6 units, of which red soil had the greatest change in pH value, followed by purple soil. The influence of infiltration solution with EC higher than 4.77 dS/m on the stable pH value of soil effluent did not increase substantially. Therefore, when irrigating with low quality water, the salt concentration in the water should be sufficiently limited according to the physicochemical properties of the soil. The research results can serve as reference for reclaimed water irrigation and calculation of water and salt transport in subtropical regions. [ABSTRACT FROM AUTHOR]

To evaluate reasonably the effect of reclaimed water irrigation salt in the soil environment, varying salinity in the effluent of salty solution leaching subtropical soil and the effect on soil chemical properties were analyzed. In this paper, five subtropical soils: clay fluvo aquic soil, sandy fluvo aquic soil, red soil, purple soil and paddy soil were selected as the research object. Use the constant head infiltration method to observe the differences in electrical conductivity (EC) and pH of effluent after leaching of soils with different concentrations of sodium salt solution (EC of solutions was 1.96, 4.77, 9.08, 17.25 and 25.06 dS/m, respectively). The results showed that the high concentration salt solution had weaker penetrating ability in red soil, purple soil and clay fluvo aquic soil with higher clay content than paddy soil and sandy fluvo aquic soil with low clay content. The same treatment achieved the same degree of penetration, and acidic soil (red soil, purple soil, paddy soil) can withstand more low quality water. In addition, the migration rate of salinity in the soil was mainly determined by the physicochemical properties of the soil. Soil clay content and exchangeable aluminum content significantly slowed the migration of salinity in the soil, while the soil silt content, EC, pH value and exchangeable calcium and magnesium content promoted the migration of salt in the soil. Salt can easily flow out through alkaline soil (clay fluvo aquic soil and sandy fluvo aquic soil). The maximum change rate of relative EC from the alkaline soil effluent was 36% higher than that of the acidic soil. The concentration of inflow salt had an obvious influence on the relative EC change rate and the penetration process of the red soil effluents, and it mainly affected the relative EC change rate for the purple soil, the clay fluvo aquic soil and the sandy fluvo aquic soil, which mainly affected the lag degree of the penetration process for paddy soil. The Boltzmann fitting showed the infiltration water salt concentration and soil physical and chemical properties had a significant impact on the model parameters (P<0.05). Moreover, the degree of soil chemical properties affected by the salt concentration in the infiltration solution was not only related to its own chemical properties, but also had a very significant relationship with the content of powder particles and clay in the soil texture (P<0.01). The concentration of salt solution had no significant (P > 0.05) effect on the pH value of alkaline soil, and had a greater effect on the pH value of acidic soil. The pH of the effluent decreased by 1.6-2.6 units, of which red soil had the greatest change in pH value, followed by purple soil. The influence of infiltration solution with EC higher than 4.77 dS/m on the stable pH value of soil effluent did not increase substantially. Therefore, when irrigating with low quality water, the salt concentration in the water should be sufficiently limited according to the physicochemical properties of the soil. The research results can serve as reference for reclaimed water irrigation and calculation of water and salt transport in subtropical regions. [ABSTRACT FROM AUTHOR]

Abstract: To evaluate reasonably the effect of reclaimed water irrigation salt in the soil environment, varying salinity in the effluent of salty solution leaching subtropical soil and the effect on soil chemical properties were analyzed. In this paper, five subtropical soils: clay fluvo aquic soil, sandy fluvo aquic soil, red soil, purple soil and paddy soil were selected as the research object. Use the constant head infiltration method to observe the differences in electrical conductivity (EC) and pH of effluent after leaching of soils with different concentrations of sodium salt solution (EC of solutions was 1.96, 4.77, 9.08, 17.25 and 25.06 ds/m, respectively). The results showed that the high concentration salt solution had weaker penetrating ability in red soil, purple soil and clay fluvo aquic soil with higher clay content than paddy soil and sandy fluvo aquic soil with low clay content. The same treatment achieved the same degree of penetration, and acidic soil (red soil, purple soil, paddy soil) can withstand more low quality water. In addition, the migration rate of salinity in the soil was mainly determined by the physicochemical properties of the soil. Soil clay content and exchangeable aluminum content significantly slowed the migration of salinity in the soil, while the soil silt content, EC, pH value and exchangeable calcium and magnesium content promoted the migration of salt in the soil. Salt can easily flow out through alkaline soil (clay fluvo aquic soil and sandy fluvo aquic soil). The maximum change rate of relative EC from the alkaline soil effluent was 36% higher than that of the acidic soil. The maximum change rate of alkaline soil outflow to EC was 36% higher than that of acid soil. The concentration of inflow salt had an obvious influence on the relative EC change rate and the penetration process of the red soil effluents, and it mainly affected the relative EC change rate for the purple soil, the clay fluvo aquic soil and the sandy fluvo aquic soil, which mainly affected the lag degree of the penetration process for paddy soil. The Boltzmann fitting showed the infiltration water salt concentration and soil physical and chemical properties had a significant impact on the model parameters (P<0.05). Moreover, the degree of soil chemical properties affected by the salt concentration in the infiltration solution was not only related to its own chemical properties, but also had a very significant relationship with the content of powder particles and clay in the soil texture (P<0.01). The concentration of salt solution had no significant (P > 0.05) effect on the pH value of alkaline soil, and had a greater effect on the pH value of acidic soil. The pH of the effluent decreased by 1.6-2.6 units, of which red soil had the greatest change in pH value, followed by purple soil. The influence of infiltration solution with EC higher than 4.77 ds/m on the stable pH value of soil effluent did not increase substantially. Therefore, when irrigating with low quality water, the salt concentration in the water should be sufficiently limited according to the physicochemical properties of the soil. The research results can serve as reference for reclaimed water irrigation and calculation of water and salt transport in subtropical regions. [ABSTRACT FROM AUTHOR]