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A long-term in situ measurement cannot fully meet the requirements of soil nitrate measurement in recent years, due to the high cost and the inability. In this study, a measurement method was proposed to collect the soil solution using the titanium sintering filter cartridge, in order to detect the nitrate concentration in the soil solution under near-infrared spectroscopy. Correspondingly, the detection device was also designed in this case. Therefore, it was demonstrated that the nitrate was suitable for the analysis at 1 250 to 1 860 nm. The commercially available Near-Infrared (NIR) Light-Emitting Diode (LED) products were combined with the 940, 1 050, 1 200, 1 310, 1 350, 1 450, and 1 550 nm NIR LED. Simulated experiments of soil solution collection were carried out using self-made soil columns. Titanium sintering filter cartridge was selected as the soil solution sampler to collect the soil solution. The results show that the soil solution collection was positively correlated with the water content of the soil, but negatively correlated with the burial depth and the clay content of the soil. It infers that the titanium sintered cartridge was suitable for sandy or clayey soils with low clay content. Once the soil moisture content exceeded 20 %, the collection time was selected as 30 min. But the collection time needed to be extended, when the moisture content was low. A systematic evaluation was made to consider the volume of solution required for the test chamber and the vertical distribution characteristics of soil nitrogen. More importantly, the optimal collection time of the soil solution was required over 60 min, where the burial depth was 10 to 40 cm. In addition, the comparative tests confirmed that the titanium sintered cartridge presented a greater capacity for soil solution collection than the LLYQ-P02 soil solution sampler, suitable for lower soil moisture contents. Finally, the BP neural network was trained using a Bayesian regularisation, with the voltage data at different wavelengths as the input layer and solution nitrate-nitrogen content as the output layer. Specifically, 70 % of all data were randomly used as the training set and the remaining 30 % as the validation set to complete the training of the nitrate-nitrogen prediction model. The feasibility and stability of the detection device were tested through the performance tests (including stability, resolution, dynamic response, and field comparison tests). The results show that the voltage tended to increase with the increasing nitrate concentration, while the voltage was lower at 1 310, 1 450 and 1 550 nm. Therefore, the presence of a large absorbance confirmed that the absorption at 1 310 and 1 550 nm was influenced by the nitrate and at 1 450 nm by water. The Pearson's correlation coefficients were 0.997 and 0.995 for the training and test set of the nitrate nitrogen prediction model, respectively. The root mean square error of prediction was 3.43 during this time. The improved prediction model of nitrate nitrogen performed the best prediction than before. The relative deviations of the measuring device from the ion electrode and the colourimetric were 5.9% max. and the absolute deviation was 9 mg/L max., respectively, fully meeting the requirements for the in-situ monitoring of nitrate nitrogen in soil solution. The new device can serve as fully automatic, non-destructive (no interference with the original soil structure), long-term, and in-situ, not available with the current nitrate ion electrodes and soil nutrient quick testers. An optimal combination of operational performance was achieved, where the standard deviation of the output voltage was 0.006, and the dynamic response time for a single wavelength was 1.4 s during the long-term operation of the detection device. The finding can provide a feasible solution for the long-term automatic measurement of soil nitrate nitrogen and the construction of a water-fertilizer integration system. [ABSTRACT FROM AUTHOR]

Soil structure is a key factor to determine the different functions of soil, such as water infiltration and retention, soil permeability, and nutrients availability. The dynamic behavior of soil also depends mainly on the tillage, crop roots, and soil organic matter return. Black soil is one of the most important arable soil with high clay content, but hard soil structure is one of the main factors limiting crop growth. It is still lacking on the effect of organic amendment on soil pore structure in the black soil. In this study, a field experiment was carried out in the black soil region located in Hailun City, Heilongjiang Province of China, in order to clarify the effects of organic amendment and depths on soil physical properties and pore structure before maize sowing in 2019. Four treatments were conducted using random block design with four replicates, including shallow tillage with maize straw return in 0-15 cm soil layer (T1), deep tillage with maize straw return (T2), or combined maize straw and organic manure return (T3) in 0-35 cm soil layer, conventional tillage without organic amendment as control. Maize straw and organic manure were also incorporated into the soil layers by shovel using manual work, where the application rates were 10 000 and 30 000 kg/hm2, respectively. CT scanning was adopted to visualize and quantify soil pore structure after maize harvesting. The constant head method was used to measure the saturated hydraulic conductivity. The results demonstrated that the bulk density under T1, T2, and T3 treatments significantly decreased 3.77%-5.66%, compared with CK, while the saturated hydraulic conductivity increased by 2.2-5.00 times, and the field water capacity increased by 6.91%-11.01% within 0-15 cm soil layer (P<0.05). T2 and T3 treatments also improved the bulk density, saturated hydraulic conductivity, and field water capacity within >15-35 cm soil layer after one maize growing season. Furthermore, the number of soil pores and porosity of >500 μm aperture under T1, T2, and T3 treatments significantly increased by 18.1%-180% and 69.2%-256% (P<0.05) in 0-15 cm soil layer, respectively, compared with CK treatment (P<0.05). Specifically, the soil pore number and porosity of >1 000 μm aperture were more 6.06%-150% and 17.4%-196% under T2 treatment than the rest. It infers that the treatments with organic amendment increased the number of soil pores with optimal distribution. In addition, the complexity and connectivity of soil pore also increased significantly, in presence of connected and sender pore. The Euler number values under T1, T2, and T3 treatments were decreased by 21.7%-54.3%, whereas, the fractal dimension under T1 treatment increased by 1.5% in 0-15 cm soil layer (P<0.05), compared with CK treatment. T2 and T3 treatments improved the soil pore structure in >15-35 cm soil layer, as shown in that the Euler decreased by 65.9%-70.5%, anisotropy, fractal dimension, and circularity increased by 50.0%-110%, 12.8%-13.9%, and 12.2%-14.9%, respectively, compared with CK treatment (P<0.05). The Euler and porosity of >1 000 μm aperture presented the largest contribution both for the bulk density and saturated hydraulic conductivity in 0-35 cm soil layer, whereas, the anisotropy and Euler presented the largest contribution for the field capacity in 0-15 cm and >15-35 cm soil layers. Pearson correlation analysis indicated that the extremely significant negative relationship was found between bulk density and saturated hydraulic conductivity, field water capacity, soil porosity within 0-15 cm soil layer (P<0.01), while the extremely significant or significant correlation was found between bulk density and all indicators, excepting for the anisotropy and Euler. Consequently, the improved physical properties of soil were attributed to the fact that the organic amendment regulated soil structure, including optimal distribution of soil pore, complex, and connectivity of pore structure. Correspondingly, the organic amendment can be expected to serve as an effective approach for the pore structure of black soil. It is also necessary to consider the response of soil pore structure in the decomposition of returned organic manure in the future. [ABSTRACT FROM AUTHOR]

The prevention and control of saline soil is of great significance to the sustainable development of agriculture in Xinjiang, and comprehensive knowledge of the Salt content of saline soil is a prerequisite for the prevention and control of salinization, so it is necessary to find an accurate and rapid method to estimate salt content information of saline soil. Ground Penetrating Radar (GPR) is widely used in geophysical and environmental assessment as a non-destructive detection technology. In recent years, this technology focuses on the detection of water content. However, the detection of soil salt is relatively weak due to the large dielectric loss in saline-alkali soil, the easily-absorbed electromagnetic wave energy the complex way to process radar signal, and even the different frequency combinations are needed to test, all of which above bring great troubles to the detection of salt. However, the rapid development of dielectric models in salinized soil makes it possible to use this technique to retrieve salt content. In order to better understand the soil salt content in drip irrigation cotton field, a typical drip irrigation cotton field was selected as the research object to be detected with a Canada's Ekko PRO series GPR multi-frequency antenna (250 MHz and 1 000 MHz). Then, the soil dielectric constant was obtained through radar amplitude envelope Average method (AEA). Soil salt content was estimated by adopting the Dobson saline soil dielectric model (Dobson dielectric model of saline soil, Dobson) as the theoretical tools. Meanwhile, the dielectric constant, soil bulk density, water content, and soil clay content were applied as the input variables of the model; Multiple Linear Regression (MLR) method was used to establish soil salinity inversion model; BP neural network (BP) was employed for simulation and prediction. Finally, the accuracy of salt content inversion by MLR model, BP model and Dobson model was evaluated based on the measured salt content. The results showed that: (l) The effective depth of GPR 250 MHz and 1000 MHz frequency antenna AEA method was 0-30 cm. (2) The dielectric constant obtained by 1 000 MHz frequency antenna AEA had a good polynomial relationship with the measured water content, and the fitting effect and accuracy of the measured water content and the inverse water content were good (R², RMSE, MER were 0.96, 1.61%, and 7.25%, respectively). (3) Among the three salt inversion models, the inversion accuracy of Dobson salinized soil dielectric model was significantly higher than that of the other two methods, with R² and RMSE of 0.91 and 0.313 g/kg respectively. Therefore, it is suitable and reliable to use GPR multi-frequency antenna AEA method to estimate soil salt content in cotton fields under drip irrigation. This method provides a new way to retrieve soil salt content and enriches the methods and means of detecting soil salt content. [ABSTRACT FROM AUTHOR]

Calcic vertisol is a typical kind of low-yield field with a total area of about 4 million hm2 in China. Calcareous concretion with particle size larger than 2 mm has been one of the representative characteristics of calcic vertisol. The limitation of soil available water is an important reason for crop failure in this region. Therefore, the curve of soil water retention dominates the estimation of available water content. However, most studies focused on the effects of calcareous concretion on soil water retention of calcic vertisol mainly under laboratory conditions. It is lacking that under field conditions. In this study, both field surveys and laboratory experiments were conducted to explore the effect of calcareous concretion distribution in 0-1 m soil profile on soil water retention. Firstly, the spatial distribution of calcareous concretion was investigated in the study plot with 150 m length, 50 m width, and 1 m depth. After then, soil profiles (0-1 m soil depth) were chosen to divide into 5 layers with a 20 cm interval. Disturbed and undisturbed soil samples were collected in each layer. Physicochemical properties were evaluated to measure the distribution of soil particle size, size and content of calcareous concretion, bulk densities of soil, and calcareous concretions. Meanwhile, the curves of soil water retention were determined using high speed centrifuge. A pressure plate method was conducted to measure water retention curves in calcareous concretion. The results showed that the mass contents of clay, silt, and sand were 30.56%-39.75%, 39.88%-45.34%, and 18.67%-24.45%, respectively, which belonged to silty clay soil in the classification standard of the United States Department of Agriculture (USDA). Clayey particles decreased, but sandy particles increased significantly with the increase of soil depth. Calcareous concretion was mainly distributed in the soil depth of >20-100 cm, where the content and size increased as soil depth increased. Calcareous concretions content in the surface soil (0-20 cm) was very low (with mass content 0.02%), where only a few calcareous concretions of 2-5 mm were discovered. The maximum content of calcareous concretion was detected at > 80-100 cm (up to 11.42%), where the calcareous concretion content was 8.04% in the size of >8-30 mm. Soil bulk density ranged from 1.23-1.61 g cm-3. The densities of calcareous concretions were 2.01, 2.21, and 2.23 g cm-3 with the size of 2-5 mm, >5-8 mm, and >8-30 mm, respectively. Soil bulk density increased along with the calcareous concretion content increasing. Water retention curves of soil and calcareous concretion were well fitted by the van Genuchten model, with the determination coefficient larger than 0.95. The saturated water content of surface soil (0-20 cm) was significantly higher than that of 20-100 cm soil. Nevertheless, the Gravitational-water content in the surface soil (0-20 cm) was much larger than that in the soil of > 20-100 cm, which was related to macropores formed during tillage. In the subsurface (>20-100 cm), soil gravitational-water content and available water-holding capacity increased with the increase of soil depth, but the field capacity and wilting point decreased. Calcareous concretion maintained a non-negligible amount of water, 0.25, 0.22, and 0.20 cm3 /cm3 in the particles with the size of 2-5 mm, >5-8 mm, and >8-30 mm, respectively. But the water-holding capacities of calcareous concretion were significantly lower than that of soil. The effects of calcareous concretion on water-holding capacity mainly occurred in the subsurface soil. Soil saturated water content, field capacity, and wilting point decreased with increasing calcareous concretion. Interestingly, calcareous concretion content was positively correlated with the soil sand content, but negatively correlated with the soil clay content. Calcareous concretion can bind soil particles together to prevent sand weathering, and thereby effectively improve soil texture. More calcareous concretion led to higher sand contents, and thus increased the available water-holding capacity in soil. This finding can provide a theoretical basis to accurately assess the soil water-holding capacity in calcic vertisol for precision irrigation and high crop productivity. [ABSTRACT FROM AUTHOR]

Accurate and rapid assessment and measurement of soil salt accumulation and spatial distribution changes are essential for preventing land degradation and improving the ecological environment. The soil Apparent Conductivity (ECa) obtained by electromagnetic induction technology can be more effective and faster to obtain soil salinity information, which helps to overcome some challenges in traditional sampling methods and reduce costs. However, the differences in soil properties among different geomorphologic types may lead to the decrease in the accuracy of EM38 in predicting soil salinity. In order to clarify the effect of soil properties on apparent conductivity under different geomorphologic types, three typical landforms (alluvial-proluvial fan edge, alluvial plain and dry delta) in Manas River Basin of Xinjiang were taken as the research objects. The apparent conductivity data of two measurement modes (horizontal mode EMh and vertical mode EMv) were obtained by using EM38 at different heights from the ground, i.e., 30 cm, 50 cm, 70 cm, 90 cm, 110 cm and 130 cm, respectively. Moreover, in each landform, 20 representative sampling points were selected for soil sample collection, with sampling depth of 0-20, 20-40, 40-60, 60-80, 80-100 cm. Soil salt content, soil moisture content, soil clay mass fraction, soil Cation Exchange Capacity (CEC) and soil organic carbon content (SOC) were determined. Firstly, path analysis method was used to analyze the influence degree and contribution rate of salt content, soil clay mass fraction, soil CEC and SOC at different depths on apparent conductivity (ECa) measured at different heights. Next, by selecting non-salinity factors with high contribution rate of ECa as auxiliary variables, a multi-factor collaborative interpretation model of soil salinity was established, and compared with the model established only with ECa as independent variable. Finally, the optimal interpretation model of soil salt content was established and the accuracy of the model was evaluated. The results showed that among the three types of landforms, soil salt content was the most important factor affecting the contribution rate of ECa, and there were significant differences in the factors affecting ECa of each soil layer under different landforms. Water content of the upper soil (0-60 cm) contributed most to ECa, whereas soil CEC content and organic carbon content of the bottom soil (60-100 cm) in the alluvial-proluvial fan edge. A high contribution was made by soil salt content at 0-20 cm layer and 40-80 cm layer, whereas CEC and clay mass fraction for 20-40 cm layer in the alluvial plain. And ECa can be significantly affected by CEC content of the upper layer (0-60 cm) and soil organic carbon content of the lower layer (60-100 cm) in the dry delta. According to the accumulative contribution rate of more than 80%, non-salt factors were selected to establish the synergistic interpretation model of layered soil salt under different landforms. The R2 adj of different soil layers under three types of landforms increased from 0.81-0.86, 0.57-0.87 and 0.27-0.47 to 0.83-0.91, 0.63-0.93 and 0.48-0.70, respectively. The accuracy verification results showed that the R2 of salt prediction models for different soil layers under three types of landforms were 0.61-0.81, 0.48-0.85 and 0.35-0.66, respectively. The research results can provide reliable theoretical basis and technical methods for rapid and accurate monitoring of saline soil. [ABSTRACT FROM AUTHOR]

Black soil in northeast China is well known as high natural fertility for grain production, but the growth and yield of crop can be limited due to the high clay content of black soil can deteriorate physical properties. In this case, both tillage and straw return can be expected to serve as the important agronomic practices, in order to efficiently improve soil physical properties. However, the optimal depth of tillage and straw return into soil for favorable soil physical properties still remained unknown, particularly in black soil region. In this study, a field experiment, referred to the depth of tillage and straw return into soil, was conducted for six years in the black soil region in northeast China, in order to investigate the effects of incorporation depth of tillage and straw return into soil on soil physical properties of black soil. Seven treatments consisted of four replicates and random block design, including no tillage (D0), shallow tillage (0-20 cm) without or with straw return (D20 or D20S), deep tillage (0-35 cm) without or with straw return (D35 or D35S), super deep tillage (0-50 cm) without or with (D50 or D50S) straw return. In the treatments with straw return, a straw rate of 10 000 kg/hm2 was set to return into the corresponding tilled soil layer. Bulk density and water holding capacity were measured using cutting ring method, while the hydraulic conductivity was determined using constant head method, and the aggregate was measured using wet sieving method. The results showed that: 1) Compared with initial soil values, D0 treatment significantly increased soil bulk density, while decreased soil porosity, water holding capacity, hydraulic conductivity and >0.25 mm water stability aggregate (WAS>0.25) within 0-20 cm soil layer (P<0.05). However, there was no significantly impact on those indicators in soil layer within 20-50 cm (P>0.05). 2) In D20, D35 and D50 treatments, there was no obvious impact on the soil physical properties within 0-20 cm soil layer with exception for WAS>0.25 in D50 treatment, but D20S and D35S treatments remarkably all indicators of soil physical properties within 0-20 cm soil layer. 3) D35, D35S, D50 and D50S treatments significantly improved soil physical properties within >20-35 cm soil layer with exception of bulk density in 2014, while D50 and D50S treatments dramatically enhanced soil physical properties within in >35-50 cm soil layer (P<0.05). Specially, aeration porosity and hydraulic conductivity increased significantly, within the corresponding soil layers, while the higher effect was found in the treatment with straw return, compared with only tilled treatments. The comprehensive evaluation also showed that D35S and D50S treatments reached the best effect for improving soil physical properties. Therefore, the findings demonstrated that deep tillage or super deep tillage with straw return can efficiently improve soil physical properties within the whole tilled soil layers, concurrently to increase the depth of tilled soil layer, and thereby to enhance the water infiltration rate and soil water storage in black soil with heavy clay. In view of the positive effect of deep tillage and super tillage with straw return on soil physical properties and the limit of no tillage, the combined tillage practices of deep tillage (or with straw return) and no tillage were proposed for the black soil with high clay in northeast China and other regions. [ABSTRACT FROM AUTHOR]

The clay layer in the vadose zone with layered structure in soils has an important effect on blocking the pollutants which will enter into the groundwater. At present, there is insufficient knowledge about the effects of the thickness of the clay layer on the migration process of nitrate nitrogen (NO3 - -N). Nitrate nitrogen is more prone to leaching through the ‘up thick and down thin’ ( the up layer of soil with larger particles and the down layer of soil with smaller particles) vadose zone with layered structure, which can cause a higher risk of nitrate nitrogen pollution to groundwater. In this study, we set up four groups soil columns with 40 cm height, the types of four groups soil columns included “up sand and down clay” and full filling with clay. The ratio of thickness (between sand and clay layer) was 3:1, 1:1, and 1:3, and the last type soil column had 40 cm clay. The content of the study in the leaching experiment under the condition of stable water head and stable concentration of nitrate nitrogen with infiltration, which included infiltration process of nitrate nitrogen solution, the characteristics of accumulation and denitrification of nitrate nitrogen in soil columns. In order to clarify the effects of the clay layer thickness on the migration process of nitrate nitrogen in the layered vadose zone, the soil columns with different thickness of clay layer. The results showed that the infiltration process of solution could be divided into two stages, namely, the relationship between the cumulative infiltration capacity with the wetting front transport depth and the infiltration time gradually changed from nonlinear to linear when the wetting front crossing the sand-clay layer interface. Meanwhile, the cumulative infiltration capacity decreased significantly with the increasing in the thickness of clay layer in the soil columns (P<0.05). When the thickness of the clay layer in the soil column reached 40 cm, the effect of blocking on the nitrate leaching of nitrogen was significantly stronger than other soil column which was with the clay layer of 10-30 cm. During the leaching experiment, a water retention layer was formed at the interface of the sand-clay layer, which made the cumulative values of nitrate nitrogen and nitrite nitrogen in the clay layer at the interface were both large, while the accumulation of nitrate nitrogen and nitrous nitrogen decreased with the increasing of depth in clay layer in the same soil column. When the difference of thickness in clay layer was not less than 20 cm during different soil columns, the accumulation of nitrate nitrogen in the soil column was significantly different (P<0.05). The soil column which thickness of clay layer was 40 cm had the largest amount of nitrate nitrogen used in denitrification [(0.15±0.05) g] was significantly higher than the soil column with 10-30 cm in the thickness of clay layer (P<0.05), which indicated that when the thickness of clay layer reached a certain degree (such as 40 cm), it not only blocked nitrate nitrogen, but also affected the amount of denitrification. Occurrence had a significant impact which could play an important role in preventing the leaching of nitrate nitrogen into groundwater. This study can provide a reference for the management of farmland fertilization and groundwater protection under soil with layered vadose zone conditions. [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]

The degradation of cultivated-layer quality of sloping farmland shows the agro-ecological process of cultivated-layer profile damaged, soil nutrient depletion and the regulation ability of crops-ecological environment declined or even completed loss on the slope scale by the combining effects of nature and human factors. In order to analyze the characteristics of soil degradation and main factors affecting degradation of cultivated layer for slope farmland in southern red soil hilly area, taking the cultivated-layer soil (0-20cm) of red soil from a small watershed as research object, we analyzed the degradation characteristics of cultivated-layer quality by cultivated-layer degradation index (CLDI), identified the dominant factors and main driving factors of cultivated-layer degradation by principal component analysis and regression analysis, analyzed the variation characteristics of soil property parameters of different degradation degrees of cultivated-layer quality, and defined the main obstacle factors and obstacle amount of the cultivated-layer quality by the obstacle factor diagnostic model for red soil sloping farmland. The results showed that the distribution area of cultivated-layer quality was mainly medium and in a mildly degraded level (accounting for 70.4% of the total samples), severely degraded samples was 11.1%, and the samples of non-degraded cultivated-layer accounting for 18.5% in red soil small watershed. The main nature driving factors leading to cultivated-layer quality degradation were rainfall, slope and soil mother material, meanwhile, agricultural input per unit of sloping farmland, tillage measure, total mechanical power per unit of sloping farmland and amount of fertilizer applied per unit of sloping farmland were the main human-driving factors. In comparison with the no degraded soil, the cultivated-layer soil properties parameters in red soil sloping farmland showed characteristics in different degradation degree. The cultivated-layer thickness was gradually thinned. The pH value first decreased significantly and then tended to be stable, and the cultivated layer of degraded level was 9.8%, and lower than that of non-degraded cultivated layer. The thinning rate of severely degraded cultivated layer was 8.9%, compared with that of non-degradation cultivated layer, which was related to the water erosion and farmer’s improper tillage methods in daily farming. The soil clay content and soil shear strength increased gradually with the deterioration of cultivated layer soil. The main obstacles of the cultivated layer quality of red soil sloping farmland with highly soil clay content, lowly pH value, thinning cultivated layer and lowly soil shear strength, and their average obstacle amount were 0.15, 0.14, 0.13 and 0.10, respectively. However, the average obstacle amount of other soil property parameters was relatively low. The obstacle amount of soil clay content, pH value and cultivated layer thickness significantly increased with the degradation degree intensifying. However, the obstacle amount of soil shear strength decreased gradually, and other soil property parameters did not change significantly, which indicated that moderately sub-soiling about 30-48 cm and reasonable fertilization were effective measures to improve the cultivated layer quality of red soil sloping farmland. Our results could provide a theoretical basis and some parameter support to scientifically understand the degradation characteristics of cultivated layer quality, define the effective measures to improve the cultivated-layer quality and construct rational cultivated-layers for red soil sloping farmland. [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 obtain the interaction parameters which can be used for discrete element simulation between the soil-engaging components and clayey black soil in northeast China, the Hertz-Mindlin with JKR Cohesion contact model in EDEM2.7 was used to simulate the clayey black soil. Aiming at the actual working environment with moisture content of 10%-20%, 2 kinds of clayey black soil with moisture content of 12.46%±1% and 17.15%±1% were prepared respectively. The rolling friction coefficient, recovery coefficient, JKR surface energy parameter and the static friction coefficient between the soil particles were used as the model calibrated parameters. The soil repose angle simulated under the simulation parameters was set as the response value. The regression model of the soil repose angle was established based on the Box-Behnken response surface method, and the regression model was optimized by using the soil repose angles under 2 moisture contents obtained by physical experiments. The optimal solution of the contact model parameters of the clayey black soil particles with 2 moisture contents was obtained. The parameter range of the discrete element contact model of clayey black soil with moisture content between 10%-20% were given. The soil repose angle and stacked shape obtained by the simulation experiment with the optimized solution had a high similarity with that of the physical test. At the same time, the static friction coefficients of 3 kinds of soil contact materials such as 65Mn plate, UHMW-PE plate and PTFE plate were tested under the conditions of 4 kinds of moisture content, which were 0, 12.46%, 17.15% and 23.5% respectively. Then for the 2 typical soil contact materials such as 65Mn and PTFE, the slope physical test bench were constructed for the clayey black soil with moisture content of 17.15%±1%. The slope simulation models of 65Mn and PTFE materials were established under the EDEM2.7 software platform. Based on the critical simulation parameters such as JKR surface energy parameter, static friction coefficient, rolling friction coefficient and recovery coefficient between soil particle and soil contact material, the simulated rolling distance of the soil ball on different soil contact materials was set as the response value. The excellent fit regression model of rolling distance for the 2 kinds of typical soil contact materials were established based on the response surface optimization method of Box-Behnkende. The 2 regression models were optimized by the sliding distance obtained by the physical experiment. Then the optimized solution of the contact model parameters of different materials was obtained. The simulation results showed that when the surface energy of JKR between soil and 65Mn was 5.5 J/m2, the recovery coefficient was 0.61, the static friction coefficient was 0.57 and the rolling friction coefficient was 0.056, the rolling distance simulation result was 153.56 mm, which was close to the average rolling distance obtained from physical experiments of 155.93 mm, and the relative error was 1.52%; When the surface energy of JKR between soil and PTFE was 4.08 J/m2, the recovery coefficient was 0.6, the static friction coefficient was 0.52 and the rolling friction coefficient was 0.045, the simulation result of rolling distance was 269.35 mm, which was close to the average rolling distance of 269.55 mm obtained from physical experiment, and the relative error was 0.07%. And the optimized parameters can be used to simulate the discrete parameters between the clayey black soil and the soil-engaging components. The study provides credible basic data for the design and simulation of agricultural machinery under clayey black soil conditions. [ABSTRACT FROM AUTHOR]