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In order to explore the effects of planting tea trees under Phyllostachys edulis forest on soil organic carbon storage and carbon components, we took pure bamboo forest, bamboo-tea mixed forest and evergreen broad-leaved forest as the study objects, collected the surface soil(0-10 cm)of these three forest types, and measured soil organic carbon(SOC), carbon components, biotic and abiotic factors. The results were as follows:(1)The diversity of understory plants in bamboo-tea mixed forest was significantly lower than that in pure bamboo forest, but there was no significant differences in soil organic carbon density[(22.54 ± 2.09)t·hm-2 ] and carbon composition between bamboo-tea mixed forest and pure bamboo forest(P>0.05). Mineral-associated organic carbon(MOC)was(20.13 ± 1.83)g · kg-1, accounting for 92.66% of total organic carbon. The soil organic carbon density of evergreen broad-leaved forest was 41.15% and 41.00% higher than that of bamboo-tea mixed forest and pure bamboo forest(P>0.05).(2)Soil microbial biomass carbon(MBC)content, 16S rRNA gene abundance, cbbL gene abundance and microbial carbon use efficiency of these forest types were(0.58 - 3.08)g·kg-1,(2.18×1010 - 5.65×1010)copies·g-1,(0.37×108-1.10×108)copies·g-1, 0.03 - 0.28, respectively. But there were significant differences about these microbial indicators between three forest types(P>0.05).(3)SOC of the three forest types was significantly negatively correlated with soil pH, gravel content and aboveground litter biomass, and significantly positively correlated with soil clay content, silt content, total nitrogen, C:N, total phosphorus and ammonium nitrogen(P<0.05).(4)In terms of different carbon fractions, particulate organic carbon(POC)and MOC were significantly negatively correlated with soil pH, gravel content and root biomass, and significantly positively correlated with soil water content, clay content, silt content, total nitrogen, C:N, total phosphorus and ammonium nitrogen(P<0.05). In conclusion, the mixed transformation of bamboo and tea will cause the decrease of understory vegetation diversity in the original pure bamboo forest, but it will not cause the decrease of soil carbon storage; compared with evergreen broad-leaved forest, it is necessary to improve the management measures of bamboo to improve its carbon sink efficiency. [ABSTRACT FROM AUTHOR]

Lily bulb is an underground tuber crop, which is mainly grown in southern China. At present, lily bulb harvesting mainly adopts manual excavation, resulting in low labor efficiency. Coupled with the high soil viscosity in lily bulb planting area, there are some problems in lily bulb mechanized harvesting, such as difficulty in fruit-soil separation and high damage rate of lily bulb. In order to solve the problems of poor separation effect, high rate of buried fruit and high crushing rate during lily bulb harvest in sticky soil, a kind of throwing roller lily bulb harvester suitable for operation in sticky soil was designed. The throwing roller lily bulb harvester is composed of vibration conveying device, throwing roller set, excavating shovel and other parts. It has the functions of vibrating crushing soil, throwing crushing soil and material conveying. It can effectively realize the secondary crushing of clay soil, and the separation effect of fruit-soil is good and does not hurt lily bulb, which is very suitable for the mechanical harvesting of lily bulb under the condition of clay soil. Combined with the growth condition of lily bulb and the requirements of planting agriculture, the motion process and separation mechanism of fruit and soil mixture on the vibration conveying device and the throwing roller set were analyzed, the dynamic model of throwing and colliding crushed soil on the throwing roller was established, and the relationship between the structure size of the throwing roller and the crushing of the clay-heavy soil block was established. Through the analysis, the structure and maximum swing Angle of the vibration conveying device, the series of throwing roll sets, the number of throwing roll teeth, the diameter of throwing roll and the contour size and other parameters were obtained. Through theoretical analysis and calculation, the structural parameters of vibration conveying device and throwing roller set of key components were determined. The length of vibration grating rod of vibration conveying device was 150mm, the distance between vibration grating rod was 50 mm, and the swing Angle of vibration grating rod was 59.12°. The number of teeth of the throwing roller wheel was 4 teeth. The radius of the throwing roller wheel was 250 mm. The spacing of the throwing roller wheel was 50 mm. According to the designed structural parameters, a prototype was built and the multi-factor test of operation parameters was carried out. The forward speed of the fruit-soil separation mechanism, the rotation speed of the throwing roller and the digging depth were taken as the test factors, and the embedding rate and crushing rate of lily bulb were taken as the test indicators. Box-Benhnken test method was used to establish the regression equation of factors and test indicators and the influence law of factors on lily bulb harvest index was obtained. When the optimum parameter combination was 0.6 m/s, 90 r/min and 170 mm, the field test values of the rate of buried fruit and the rate of broken lily bulb were 6.3% and 7.1%, respectively. The performance of the machine met the design requirements. The research results can provide reference for the research of mechanization harvesting technology and equipment of lily bulb. [ABSTRACT FROM AUTHOR]

To achieve the carbonization utilization of Triarrhena lutarioriparia straw and relieve the environmental pressure caused by improper disposal in the Dongting Lake area, the agricultural efficiency of biochar derived from Triarrhena lutarioriparia was clarified. Two typical paddy soils in southern China, namely reddish clayey soil developed from a Quaternary laterite parent material and granitic sandy soil developed from a granite parent material, were selected. Six treatments with different dosage of biochar (0, 1%, 2%, 4%, 6%, and 8% of the soil mass，0-20 cm soil depth) were set. Rice pot experiments were conducted in 2020 to study the effects of different application rates of Triarrhena lutarioriparia biochar on rice nutrient utilization characteristics in two typical soils. The results showed different application rates of Triarrhena lutarioriparia biochar and soil types had certain effects on dry matter accumulation and nutrient uptake by rice organs and aboveground structures. With the addition of biochar, compared with the treatment without biochar, the accumulation of dry matter of rice increased from 0.6% to 18.6% and from 15.5% to 42.4% in the granitic sandy soil and reddish clayey soil, respectively. With the addition of 4% biochar, the accumulation of nitrogen, phosphorus, and potassium nutrients in the rice plant of the treatment increased by 8.6%, 10.5%, and 82.5% in the granitic sandy soil and by 33.8%, 100.0%, and 125.3% in the reddish clayey soil, respectively. The quadratic regression equation and fertilizer – carbon coupling model fitting showed that the optimal addition amounts of biochar in the granitic sandy soil and reddish clayey soil were 2.51% and 4.80% for nitrogen utilization, 4.33% and 7.03% for phosphorus utilization, and 4.67% and 4.81% for potassium utilization, respectively. Therefore, the application of Triarrhena lutarioriparia biochar is conducive to promoting the accumulation and growth of nitrogen, phosphorus and potassium nutrients in rice, and the amount of biochar added and soil conditions are important factors affecting the coupling effect of fertilizer and carbon. [ABSTRACT FROM AUTHOR]

Selenium (Se) is a trace element that plays a crucial role in human health. It has antioxidant, anti-cancer and anti-viral properties and is essential for a healthy body. The level of Se in the human body is largely dependent on daily dietary intake, which is in turn influenced by the amount of Se that enters the food chain from the soil. The global distribution of Se in soil is uneven, with a large difference in concentrations ranging mainly between 0. 01- 2. 0mg / kg. The average abundance of Se in the Earth’s crust is 0. 07mg / kg, but in some Se-enriched areas, it can reach up to 1200mg / kg. The chemical behavior of Se in soils is complex and diverse, involving processes such as adsorption - desorption, precipitation - dissolution, oxidation - reduction, methylation - demethylation and complexation reactions, each of which affects the bioavailable Se and is influenced and conditioned by factors such as soil pH, soil organic matter, metal oxides, clay and microorganisms. Roots are the primary site for most plants to absorb Se, which is then transported, metabolized, and accumulated. Plants can directly absorb Se from the soil, including Se that exists in the form of free ions, carbonate-bound Se, and Se adsorbed on the surfaces of clay and humus in soil solutions. However, selenite and selenate can be reduced to solid, insoluble Se(0) and metalSe precipitates that are not bioavailable in locally anaerobic areas (such as soil aggregates) or used by bacteria as terminal electron acceptors. Previous researchers have conducted a lot of work on chemical extraction methods, but there are still problems, such as insufficient extraction specificity and Se form transformation during the extraction process. Hence, an accurate approach for predicting the amount of soil Se that can be absorbed by plants is essential. However there are no clear paths for the choices of assessment methods and influencing factors of soil Se bioavailability. These problems have restricted the utilization of Se -enriched land resources. Thus, providing a scientific basis for the development and utilization of Se-enriched land resources is the goal here by summarizing the main assessment methods and dominant factors on soil Se bioavailability. Determining the activity of Se in soils comprehensively requires considering the complicated and varied effects of natural conditions on its bioavailability, which can be studied through characterization methods and identification of influencing factors. Therefore, it is of practical importance and a challenge to accurately determine the form of Se in soils and assess its bioavailability. Current methods for characterizing the bioavailability of soil Se include the traditional chemical extraction methods ( single extraction and sequential extraction) and the emerging Diffusive Gradients in Thin films (DGT) technique. Chemical extraction is a process that involves separating a specific component or substance from a mixture using a solvent or a chemical reagent. The extraction method depends on the physical and chemical properties of the substance being extracted and the nature of the mixture. The general steps involved in a chemical extraction method are: choosing the appropriate solvent or chemical reagent that can selectively dissolve the desired substance while leaving the unwanted components behind, mixing the mixture and the solvent / reagent together to allow the selective extraction of the desired substance, separating the extracted substance from the mixture using various techniques such as filtration, centrifugation, or evaporation, and purifying and isolating the extracted substance by further chemical or physical methods if necessary. The DGT technique is an effective environmental chemistry method used for identifying elements and compounds in various aqueous environments, including natural waters, sediments, and soils. This technique is particularly useful for detecting bioavailable trace elements, and it can be applied for in - situ detection. The DGT technique involves using a specially-designed passive sampler that comprises a binding gel, a diffusive gel, and a membrane filter. The element or compound of interest passes through the membrane filter and diffusive gel before being assimilated by the binding gel in a rate-controlled manner. Subsequently, the binding gel is analyzed post-deployment, enabling the determination of the time-weighted-average bulk solution concentration of the element or compound via a simple equation. The advantages and limitations of chemical extraction methods, DGT technique and bioavailability assessment models of Se at a regional scale are compared. Traditional chemical extraction procedures such as single extraction or sequential extraction can be used to characterize the bioavailability of Se in the soil, to a certain extent. Still, the extraction process has many limits and incomplete extraction problems. The DGT method can be used to simulate the root uptake process of plants and can better characterize the bioavailability of Se compared to sequential extraction. One of the major advantages of the DGT technique is its ability to provide accurate and reliable results, even at low concentrations. Additionally, this technique is non-destructive and can be used in-situ, making it suitable for real-time monitoring of environmental conditions. However, there are also some limitations associated with the DGT technique. For instance, the binding gel used in this method may not be specific to the target element or compound, leading to the possibility of cross-reactivity with other substances. Additionally, the technique may be influenced by factors such as temperature, pH, and ionic strength, which could affect the accuracy of the results. Using large-scale crop-root soil samples, a soil-crop Se assessment model was developed with parameters of physicochemical indicators ( e. g. soil pH, soil organic matter, soil Se, etc. ), which can better predict Se bioavailability on a regional scale. Some major and minor influencing factors affecting the uptake of Se in soil by plants are discussed. In short, topography and soil type, Se species, pH and organic matter are the main factors affecting bioavailable Se, with plant species and soil aging as secondary factors. In brief, the main limitations of the characterization methods for the bioavailability of different forms of Se are: a single extraction method can be affected by soil properties, soil / solution ratio, extraction time, the pH value of the extraction agent, and other factors. Sequential extraction methods have problems with incomplete extraction, dilution of the extract, and Se loss during centrifugation and filtration. These traditional methods cannot be used to reflect the dynamic processes of the solid - phase soil - solution - root system. DGT technology is a method that disturbs the equilibrium between soil solution and solid phase, simulating the dynamic process of Se uptake by roots, and has advantages in assessing bioavailability. However, it is still questionable whether it can be used to fully predict the replenishment dynamics of Se in field soil. The main factors affecting the bioavailability of soil Se are: (1) Topographical factors such as altitude, slope, and terrain wetness index, which have some influence on soil Se content; there are large differences in organic matter, iron / aluminum hydroxides, and pH among different soil types, which can be controlled to affect Se migration and bioavailability; (2) Soluble and exchangeable Se are more easily absorbed by plants, and selenate with better mobility is easier to absorb, transport, and metabolize in plants than selenite; (3) Increasing soil pH can generally improve Se bioavailability, but this is not the case in organic-enriched soils. Currently, there is no universally applicable method for evaluating soil Se bioavailability, as it is influenced by many factors such as topography, soil type, and soil physicochemical properties. This makes it difficult to compare and verify different results. Improving in-situ DGT analysis technology and modifying the analysis of Se forms are important technical means for accurately evaluating soil Se bioavailability and are also important directions for future development. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICP) is one widespread approach to soil clay improvement in sustainable biological engineering in the world. The green and efficient approach can also greatly contribute to a series of environmental and ecological challenges. Among them, urea-producing bacteria can be used to induce calcium carbonate precipitation for better soil consolidation. Bacterially generated urease enzymes can decompose the urea to further promote the binding of Ca2+ and CO32-. Therefore, the calcium carbonate precipitation can be expected to apply to desertification combating. However, the urea-producing bacteria can be limited to environmental adaptability and weak function in a harsh desert environment. Many technical bottlenecks are urgent issues for the sand-fixation using calcium carbonate precipitation induced by urea-producing bacteria. It is a high demand to develop native urea-producing bacteria. In the preliminary research, the strain of Sporosarcina pasteurii was identified from the aeolian soils in the Mu Us desert. In this research, the optimal reaction conditions were determined to verify the sand-fixation effect in the desert soil after optimization. A series of single-factor experiments were designed during 0-72 h with the different experimental gradients by pH (7, 8, 9, and 10), bacterial inoculum (1%, 2%, 3%, 4%, and 5%), the ratio of bacterial and cementing solution (25%, 50%, and 75%), and temperature (30, 35, and 40 ℃). The initial urease activity and calcium deposition rate were tested using the response surface method. The optimal reaction factors and conditions were then determined from the six factors (reaction time, pH, bacterial inoculum, the ratio of bacterial and cementing solution, reaction temperature, and initial urease activity). The sand-fixation experiments were carried out on the aeolian soil from the Mu Us desert under optimized conditions. Mineral morphologies and properties were then characterized by the scanning electron microscope (SEM). The thickness and hardness of the soil consolidated layer, soil particle distribution, soil organic matter and calcium carbonate content were measured to calculate the erodibility factor (EF) under soil wind erosion. The results showed that: 1) The main reaction drivers of calcium carbonate precipitation were determined as the reaction temperature, reaction time, pH value, as well as the ratio of bacterial and cementing solution. An optimal combination of conditions was achieved at 34.47 ℃, 71.68 h, pH 7.73, and 74.94% ratio. In this condition, the maximum rate of calcium deposition was 42.33%. 2) The calcium carbonate precipitation was obtained in the polycrystalline phase composition with the cubic, rhombic, spherical, and amorphous under the optimized conditions. Diverse calcium carbonate precipitation was formed on the surface of sand grains, or embedded in the sand grains. 3) Sand-fixation by induced calcium carbonate precipitation was significantly enhanced after optimization. The number of sand particles increased significantly (P<0.05), and the thickness and hardness of the soil consolidated layer increased by 5 and 10 times, respectively. The contents of organic matter and calcium carbonate increased significantly, whereas, the wind EF decreased from 0.94 to 0.66. Therefore, the urea-producing bacteria-induced calcium carbonate precipitation can serve as the new effective and favorable sand fixation for desertification combating in the future. It is still necessary to develop the distribution of simultaneous ecological restoration, in order to gradually promote this new technology in large-scale field experiments. Consequently, in the field application, the sand fixation effect can be enhanced to further determine the application time and water under suitable conditions and the soil compaction will be avoided by appropriately breaking. [ABSTRACT FROM AUTHOR]

Based on the soil temperature and humidity data of soybean farmland under conservation tillage in Northeast China in the published article, the impact of conservation tillage measures on the soil hydrothermal status of soybean farmland in Northeast China was quantitatively assessed by using conventional tillage (CT) as a control, no-tillage (NT), reduced tillage (RT), straw mulching (SM), and no-till straw mulching (NTSM) as treatments. The results showed: compared with CT, conservation tillage increased the soil volume water content of 0-170cm soil layer in soybean farmland in Northeast China by 9.2%, and reduced the temperature of the shallow soil layer (0-30cm) by 8.2%. Four conservation tillage could increase soil moisture under different climatic conditions; straw mulching could increase soil moisture content throughout the growth period of soybeans, and the effect on soil hydrothermal was greatest during the nutrition period of soybean, and soil temperature increased with the increase of straw mulching; the magnitude of soil temperature reduction by conservation tillage decreases with the decrease of soil clay particles, the magnitude of soil moisture increased by conservation tillage decreases with the increase of soil depth. Among them, NTSM at different soil depths was the most obvious effect of water storage and moisture retention, and the soil moisture in the soil layer of 0-20cm was increased by 32.9%. In summary, conservation tillage could increase soil moisture but reduce soil temperatures. Temperature, precipitation, growth period, straw mulching amount, soil type and soil depth all had an impact on soil hydro-thermality in soybean farmland under conservation tillage. [ABSTRACT FROM AUTHOR]

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]

Based on the farmland scale of Zhanghe irrigation district and the field data of farmers' survey results and literature survey, the spatial heterogeneity of local rice irrigation water productivity and its influencing factors were analyzed, and the key influencing factors of irrigation water productivity were screened by using correlation analysis and partial least squares regression analysis. The results showed that: (1) in Zhanghe irrigation district, the rice yield in the main canal and the fourth main canal control villages was the minimum value and the irrigation water productivity in the third main canal control villages was the maximum and that of the main canal control villages was the minimum. (2) Irrigation water productivity showed a very significant negative correlation with irrigation water consumption per unit area, daily average solar radiation and soil silt content, and a very significant positive correlation with daily average temperature and soil clay content. (3) Irrigation water productivity was greatly affected by irrigation water consumption per unit area, nitrogen application rate, daily average temperature during growth period, daily average solar radiation and soil clay content. Therefore, management measures and meteorological factors are the key factors to improve rice irrigation water productivity in Zhanghe irrigation district. The research results will help to provide data support for improving local rice management level and irrigation water productivity. [ABSTRACT FROM AUTHOR]

【Objective】 This paper aimed to explore effects of reduced chemical fertilizer and soil texture on yield, quality and nitrogen（N）, phosphorus（P） and potassium（K） fertilizer utilization rate of flue-cured tobacco. 【Method】 Using flue-cured tobacco variety K326 as material, a field experiment was established in sandy soil, clay soil and heavy loam in Qujing tobacco production site, and six fertilization treatments were set up, i.e., T1（CK）（conventional dosage of N, P, K）, T2 and T3（deduced fertilizer N, P, K proportion by 10% and 20%, respectively）, T4 and T5（organic fertilizer replacing 10% and 20% chemical fertilizer, respectively） and T6（no manure or fertilizer）. 【Result】Compared with treatment T1（CK）, treatments T2, T3 significantly improved grade, yield, economical output and N, P, K use efficiency of tobacco leaves in sandy soil. Meanwhile, treatments T2, T3 increased contents of potassium, decreased total sugar, reducing sugar. The contents of total nitrogen, nicotine and water-soluble chloride in the middle and upper parts of leaves were not significantly affected; and the chemical composition was more balanced under T2 and T3. Compared with treatment T1（CK）, treatment T2 and T5 did not significantly improved growth of the tobacco plants in clay soil, but the proportion, yield, output and N, P, K use efficiency under T2 and T5 in tobacco leaves were significantly higher than that of T1（CK）, and the chemical composition of middle and upper position leaves was more balanced. Compared with T1（CK）, treatments T2, T3, T5 had no effect on tobacco plant growth in heavy loam, but improved the proportion of products, yield, output, N, P, K use efficiency of tobacco. Furthermore, the contents of total sugar, reducing sugar of middle and upper part leaves were increased under T2, T3 and T5. The total nitrogen, nicotine, potassium and water-soluble chloride were not affected by treatments. And treatments T2, T3 significantly improved the balance of chemical composition of tobacco leaves. Under the same N, P and K application rate, the N and P uptake and use of tobacco plants in different soils could be sorted as the following: Sandy soil>heavy loam>clay soil, and K use efficiency as the following: Heavy loam>clay soil>sandy soil. 【Conclusion】Based on the current N, P and K usage of tobacco in farmlands, the potential N, P and K proportion of chemical fertilizer reduction（CR） or replacement with organic fertilizer（ROR） in sandy soil was 10%. The N, P and K proportion of CR or ROR in clay soil was 10%-20%. The potential reduction of N, P and K fertilizer in heavy loam was 10%, and the potential proportion ROR was 10%-20%. [ABSTRACT FROM AUTHOR]

The effects of irrigation on winter wheat yield and water use efficiency (WUE) were mostly explored based on site-based experiments in North China Plain (NCP) region. However, due to the influences of contrasting environmental factors (e.g. climate and soil properties), these results cannot be accurately cross-compared among different studies, resulting in the difficulty to get the generalizable pattern at regional scale. Here meta-analysis was conducted to comprehensively evaluate the effects of irrigation on winter wheat yield and WUE in NCP region, with the observation data of 1876 pairs from 186 field experimental papers totally. The differences of the irrigation effects in different regions, precipitation year types, soil texture, and nitrogen (N) application levels were explored, and the corresponding optimal irrigation amounts for reaching high yield and WUE were ascertained. Results showed that compared with non-irrigation during the winter wheat growing period, irrigation increased the yield of winter wheat in NCP by 32.0%-38.3%, and reduced the WUE by 27.1%-30.1%. The yield increment due to irrigation in the northwest of NCP (39.6%-53.5%) with total precipitation during the winter wheat growing period below 150mm was higher than that in the southeast of NCP (24.3%-27.1%) with total precipitation during the winter wheat growing period higher than 150mm, while the decrease of WUE due to irrigation in northwest of NCP (32.4%-37.5%) was higher than that in the southeast of NCP (22.0%-24.3%). The optimum irrigation amount for high yield and WUE of winter wheat was 150-180mm in the northwest and 120-150mm in the southeast. Specifically, for different precipitation year types, the optimum irrigation amounts were 120-150mm with 2 times during jointing and flowering stages for dry year, during jointing and heading stages for normal year, and during jointing and booting stages for wet year. For different soil texture, irrigation under loamy soil had the highest increases in yield, while clay soil had the lowest decreases in WUE; the optimum irrigation amounts of winter wheat with four different soil texture of sandy soil, loam, clay loam and clay were 60-90mm, 120-150mm, 180-210mm, and 150-180mm, respectively. For different N application levels, N application of 120-240kg.ha-1 led to the highest yield and WUE under the irrigation amounts of 80-140mm, of which the higher yield was obtained under irrigation amounts of 110-140mm, and the higher WUE was obtained under the irrigation amounts of 80-110mm. Collectively, the NCP region can achieve the goals of high yield and WUE when irrigation amount was 120-150mm with 2 times but at different stages during different precipitation year types (i.e. dry year, normal year and wet year). Meanwhile, the combination of loam conditions with the N application of 120-240kg.ha-1 can synergistically improve the yield and water use efficiency of winter wheat. [ABSTRACT FROM AUTHOR]

[ Purpose] The present paper aimed to study the physical properties, soil enzyme activities and their correlation characteristics of wild Bletilla striata soil in different producing areas in Guizhou, so as to provide a theoretical basis for realizing high yield and quality of B. striata artificial cultivation. [ Method] 8 soil sample plots for the wild B. striata were collected in Guizhou province to detect and analyze the soil physical and enzyme activity index characteristics and the correlation between them. [ Result]The soil density was between 2. 06 -2. 55 g/ cm³ with weak variation. The soil texture was mainly clay loam and sandy loam. In most soils, the proportion of the > 0. 25 mm size soil water-stable aggregates reached 70% . The distribution of the soil water-stable aggregates size fraction were different, 2 - 5 mm size fraction was the dominant size fraction in 4 soil plots, < 0. 25 mm size fraction was the dominant size fraction in 3 soil plots. The dominant size fraction of soil micro-aggregate was 0. 25 -0. 05 mm size fraction. The activities of urease, acid phosphatase and sucrase in soil were significantly different with strong variation. The activities of catalase in soil were not significantly different with weak variation. Soil enzyme activity was strongly influenced by the soil density, soil aggregates and microaggregates. There was a significant positive correlation between urease and acid phosphatase, which could promote each other. [Conclusion] Guizhou wild B. striata has strong adaptability to soil environment. It mainly grows in sandy soil or clay with soil clay content less than 25 %, and some wild B. striata can also grow in clay with soil clay content more than 30% ; Soil specific gravity, soil aggregates and micro aggregates are important factors affecting soil enzyme activity of B. striata. The suitable soil specific gravity is 2. 06 - 2. 55 g/ cm³, the dominant particle size is 2 - 5 mm or < 0. 25 mm, and loam is the best soil texture; Urease and acid phosphatase can promote each other. [ABSTRACT FROM AUTHOR]

In order to provide a theoretical basis for the evaluation of carbon sequestration potential, we analyzed the adsorption characteristics and influencing factors of dissolved organic carbon（DOC）in typical farmland soils with different fertilization treatments in China. Four typical farmland soils, namely black soil, gray desert soil, fluvo-aquic soil, and red soil, were selected to apply different fertilizer levels of no fertilizer（CK）, chemical N fertilizer（N）, chemical NP fertilizer（NP）, chemical NPK fertilizer（NPK）, and NPK plus organic manure（NPKM）to determine the DOC adsorption capacities by the equilibrium adsorption method. The results showed that the DOC adsorption capacities of different types of soils at the same equilibrium concentration were very different, and were generally in the order of gray desert soil and red soil>black soil>fluvo-aquic soil.Q max appeared in the order of red soil>gray desert soil>black soil>fluvoaquic soil in various soils. Among them, the adsorption characteristics of each soil type were quite different under different fertilization treatments. The general trend ofQ max in the gray desert soil and fluvo-aquic soil under different fertilization treatments were NPKM>NPK> NP>N>CK and in red soil was NPKM>N>NPK>NP

The sandy clayey purple soil is widely distributed in the middle and upper reaches of the Yangtze River, serving as one of the main soil resources in the mountainous areas of southwest China. Intense physical weathering, loose structure, and low erosion resistance are the main characteristics of sandy clayey purple soil. Therefore, environmental disturbance, such as the water fluctuation near reservoirs, heavy rainfall, and groundwater, often induces soil erosion, landslide, settlement, and soil-water disasters of purple soil. A serious threat has been posed on the village buildings and roads, even the agricultural production. The properties of water immersion disintegration with the sandy clayey purple soil can also be an important reason for water and soil disasters in the southwest mountainous areas. It is necessary to clarify the disintegration characteristics and reinforcement for the water-soil disasters prevention and control. In this study, a disintegration test was performed on the purple soil samples with different initial dry densities, water content, and grain gradation using a self-developed instrument. Meanwhile, the disintegration and evolution of sandy clayey purple soil were also analyzed from the perspective of unsaturated effective stress. Bacillus megaterium was selected to reinforce the soil samples with the Microbial Induced Calcite Precipitation (MICP), as the more suitable as Sporosarcina pasteurii in the sandy clayey purple soil areas. A Scanning Electron Microscope (SEM) was then utilized to characterize the morphologies of the soil sample, thereby determining the MICP improvement on the disintegration characteristics of sandy clayey purple soil. The results show that: 1) Four stages were divided in the whole process of immersion and disintegration of sandy clayey purple soil, including the air-water conversion, equilibrium, disintegration development, and disintegration residual stage. 2) The initial dry density, water content, and grain gradation obviously affected the disintegration characteristics of sandy clayey purple soil. Specifically, the disintegration rate and the average disintegration velocity decreased, with the increase of initial dry density and water content. In addition, the average disintegration velocity of soil increased by the content of fine particles. 3) The evolution of water and air was ranging from the pore water closed, double connected, and pore air closed morphology, with the increasing of the initial saturation. Water was rapidly absorbed into the pores under the matric suction, where the pore pressure was changed significantly. Subsequently, the effective stress of unsaturated soil rapidly reduced to the negative, leading to an interparticle compressive stress (the negative tensile stress). Once the tensile stress reached the value of effective cohesion, the unsaturated strength of purple soil was lost completely. Finally, the soil sample was then destroyed under disintegration. The more severe disintegration was also obtained with the decrease in the initial saturation of a soil sample. The decay process of the unsaturated effective stress depended greatly on the initial saturation after the purple soil was immersed in water. Specifically, the average disintegration velocity attenuated exponentially with the increase of the initial saturation. 4) The disintegration rate and the average disintegration velocity of the MICP treated soil samples decreased by 73 to 97 percentage points and 84%-99%, respectively, compared with the untreated soil. Calcium carbonate crystals formed by solidification and deposition greatly reduced the micro-cracks and large pores in the soil structure. As such, a denser pore structure was achieved to enhance the strength of intergranular cementation for the higher resistance to the disintegration of the soil. Consequently, the MICP technology can serve as an effective measure to prevent the water and soil disasters of the sandy clayey purple soil in southwest mountainous areas. [ABSTRACT FROM AUTHOR]

[Objective]The present paper aimed to determine the stable nutritional quality of sweet potato under which soil texture, and to determine the main soil nutrient factors that affect the nutritional quality. [Method] Collecting 60 plant samples of sweet potato variety Gaoxi-14 and 60 bags of non-rhizosphere soil samples, the soil texture, 8 soil physical and chemical indexes and 5 sweet potato nutritional quality indexes were determined and analyzed. [Result] The coefficient of variation of the nutritional quality indicators of sweet potato, including amylose, amylopectin, total starch, soluble sugar and protein, was smaller in clay loam and loam, and larger in clay soil. Sweet potato amylose in loam was mainly negatively affected by pH, and the soluble sugar content was significantly higher than that in clay. Sweet potato amylose and amylopectin in clay loam were mainly affected by ammonium nitrogen positively and negatively. Sweet potato amylose and amylopectin in clay were mainly negatively affected by organic matter. [Conclusion] Loam soil and low pH are beneficial to produce stable quality and high amylose sweet potatoes, clay loam and high ammonium nitrogen are beneficial to produce stable quality and high amylose sweet potatoes, clay loam and low ammonium nitrogen are beneficial to produce stable quality and high branched chains starchy sweet potato. [ABSTRACT FROM AUTHOR]

Salt washing is an important test process for remolding carbonate saline soil. In order to study the changes of physical properties and partial mechanical properties of remolded carbonate saline soil before and after salt washing, the typical carbonate saline soil（silty clay） in Durbert area of Songnen Plain was selected for salt washing treatment. The salt content, liquid and plastic limit, optimal dry density and optimal water content before and after salt washing were determined. At the same time, the triaxial test was carried out to determine the changes of shear strength, cohesion and internal friction angle before and after salt washing. It was found that salt washing lead to the decrease of soil salt content, optimal water content and cohesion. The liquid limit of saline soil decreased from 30.1 % to 20.2 %, and the plastic limit decreased from 15.6 % to 11.3 %. The shear strength and internal friction angle increased. At the same time, the soil gradation changed, and the soil also changed from silty clay to silty soil. [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]

Excessive application of nitrogen fertilizer aggravates nitrogen losses from agricultural soils, with effects such as increasing ammonia（NH3）volatilization, nitrous oxide（N2O）emissions, and nitrate（NO3）leaching, which can reduce air and water quality and have a negative impact on global climate. Urease inhibitors and nitrification inhibitors can delay the transformations of soil nitrogen and reduce the negative effects of soil-reactive nitrogen. Both have been widely used in agricultural production, as N-butylthiophosphoryl triamine （NBPT）, 3, 4-dimethylpyrazole phosphate（DMPP）, and dicyandiamide（DCD）. The mechanisms of urease inhibitor（NBPT） and nitrification inhibitors（DMPP, DCD）in agricultural soils and their effects on the environment and agronomy were comprehensively reviewed in this study, revealing the main factors affecting the effectiveness of its application. Many studies have shown that NBPT combined with chemical nitrogen fertilizer and/or organic fertilizer could reduce NH3 volatilization, N2O emission, and NO3 leaching, as well as improve crop yield and quality and nitrogen-use efficiency. Similarly, as nitrification inhibitors, both DCD and DMPP could reduce soil N2O emissions and NO 3 leaching, increase crop yield, and increase soil NH3 volatilization loss. The inhibition efficacy of urease /nitrification inhibitors is related to the type of nitrogen inhibitors, the form and rate of nitrogen fertilizer, whether rainfall or irrigation is employed, and edaphic conditions such as soil pH and clay content. Therefore, the characteristics and effects of urease / nitrification inhibitors should be considered for scientific and practical applications. [ABSTRACT FROM AUTHOR]

BACKGROUND: Soil limit water content is an important basis for fine-gmined soil classification and engineering property evaluation. Additionally, it is an important evaluation index for clay exploration and industrial utilization. Inaccurate test results of soil limit water content may lead to serious engineering safety accidents and personal and economic property losses. Certified reference materials (CRMs) are important for ensuring the accuracy, comparability, and effectiveness of the analyzed data. However, no certified reference materials for soil limit water content exist; therefore, the preparation of CRMs for the soil limit water content holds great significance. OBJECTIVES: To prepare CRMs of soil limit water content. METHODS: In strict accordance with the specifications and standards, such as "Technical Specifications for Finst -Class Reference Materials" (JJF 1006-1994) and General Principles and Statistical Principles for the Valuation of Reference Materials (IF 1343-2012), five standard materials of soil limit water content (GBW07969, GBW07970, GBW07971, GBW07972, and GBW07973) have been developed. These samples were collected from Huaibei of Anhia province, Datong of Shanxi province, and Nanjing of Jiangsu province. After artificial crushing, drying, and sterilization, the samples were finely crushed to less than 0.25mm by a large ball mill. After particle size analysis, the samples were bottled and numbered in a clean room. RESULTS: Twenty-five bottles of each sample were randomly selected for homogeneity testing. All the measured values of F were less than Faes(24, 25) =1.96, and the relative standard deviation (RSD) was between 1. 16% and 2, 67%, which indicated good uniformity. There were no significant differences in the long-term stability test (12 months) and the short-term stability test (60°C, -20°C). The certified values of 10mm liquid limit, plastic limit, and plasticity index were 26. 3% -39.9%, 16.9% -22.2%, and 10.0% - 17.7%, respectively. The gradient series was significant, which included silty clayey and clayey type of soils. CONCLUSIONS: Five fint classes of National CRMs (GBW07969, GBW07970, GBW07971, CBW07972, and GBW07973) of soil limit water content were successfully prepared. This series of CRMs can be used for calibration of instruments and equipment, quality control, capability verification, and other technical quality activities, which provide a guarantee for the accuracy requirements of soil limit water te data in hydraulic environment geological exploration, protechnical engineering explontion, clay mine exploration, and other related disciplines. [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]

[Objective] To study the impact of coal dust generated by open-pit coal mining activities in arid areas on the physical and chemical properties of soil and soil erodibility in surrounding areas. [Method] The representative Hongshaquan coal mine in Zhundong coal field in Xinjiang was selected as the research area. Collect soil samples within 2000 m from dumps, coal dumps, and mining areas, analyze soil physical and chemical properties and calculate erodibility factor (EF) values, explore the relationship between soil physical and chemical properties and (EF) values, and analyze their spatial distribution laws [Results] ① Coal dust deposition has different degrees of impact on various physical and chemical properties of soil, among which organic matter has the most significant impact, showing an exponential distribution from high to low with distance. The particle structure of the surface soil of the dump is significant with other sampling points The difference is that the sand content of the soil surface layer is significantly reduced, and the soil clay content is significantly increased. ② The soil EF value has a very significant positive correlation with soil pH, soil total phosphorus, and soil sand content (P<0.01), and has a positive correlation with soil organic matter, The content of soil clay particles and powder particles showed a very significant (P<0.01) negative correlation. The order of correlation is pH> clay particles> organic matter> sand particles> powder particles> total phosphorus> calcium carbonate> total salt> bulk density> total Nitrogen. ③The coal dumps and dumps formed by coal mining activities play a role in reducing soil erodibility. The soil EF value reaches the lowest value at the coal dump, and the soil EF value in the coal mine area is also significantly smaller than the surrounding areas. [Conclusions] ] Coal mining activities have a significant impact on the physical and chemical properties of the soil around the mining area, thereby reducing soil erodibility. [ABSTRACT FROM AUTHOR]

To clarify the degradation behavior of pyraclonil in the environment. The indoor simulation test method was used to study the degradation characteristics of pyraclonil in purplish soil, paddy soil and red soil under the conditions of anaerobic, aerobic and sterilized. The results showed that the degradation of pyraclonil in those three soils accorded with the first-order kinetic equation. Under aerobic conditions, the degradation half-lives in purplish soil, paddy soil and red soil were 13.4 d, 10.1 d, and 31.1 d, respectively. And the degradation rates were positively correlated with the organic matter and clay content in the soils. The degradation rates under different conditions were in the order of anaerobic > aerobic > sterilization, which indicated that the degradation of pyraclonil in the soil was affected by the hydrolysis and microbial activity. Within a certain range of soil water holding capacity, the degradation rate of pyraclonil in the soil was improved with the increase of soil water content. This study demonstrated that the degradation rate of pyraclonil was relatively fast and the residue period was short under the condition of flooding in paddy field. This work provided a scientific basis for the rational use of pyraclonil and its environmental safety evaluation. [ABSTRACT FROM AUTHOR]

To clarify the degradation behavior of pyraclonil in the environment. The indoor simulation test method was used to study the degradation characteristics of pyraclonil in purplish soil, paddy soil and red soil under the conditions of anaerobic, aerobic and sterilized. The results showed that the degradation of pyraclonil in those three soils accorded with the first-order kinetic equation. Under aerobic conditions, the degradation half-lives in purplish soil, paddy soil and red soil were 13.4 d, 10.1 d, and 31.1 d, respectively. And the degradation rates were positively correlated with the organic matter and clay content in the soils. The degradation rates under different conditions were in the order of anaerobic > aerobic > sterilization, which indicated that the degradation of pyraclonil in the soil was affected by the hydrolysis and microbial activity. Within a certain range of soil water holding capacity, the degradation rate of pyraclonil in the soil was improved with the increase of soil water content. This study demonstrated that the degradation rate of pyraclonil was relatively fast and the residue period was short under the condition of flooding in paddy field. This work provided a scientific basis for the rational use of pyraclonil and its environmental safety evaluation. [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]

Rice-wheat rotation area, with heavy clay soil texture, that it is wheat planting area accounts for more than 37% of the total wheat sowing area in China as one of the major grain production bases, and rice-wheat rotation is the main cropping pattern in this region. Meanwhile, because of the shortage crop stubble and more rainfall in autumn, which lead to serious wet damage during the tilling and seeding stage for this field. Currently, most of the existing no-tillage and less-tillage seeding equipment for wheat sowing in rice stubble areas were optimized and developed on the basis of traditional contact-type wheat seeding technology, which lead to adhesion and serious blockage phenomenon, as well as increasing of operating resistance and power consumption during working. Therefore, a innovative technical proposal of non-contact type pneumatic seeding technology that could avoid contacting between sowing parts and soil was introduced in this paper, which in order to solve the problems of soil adhesion, blockage, drag increment as well as poor sowing quality for wheat seeders under the condition of sticky heavy loam clay in rice-wheat rotation areas. Experiment that utilized a self-made platform for wheat pneumatic seeding was conducted, which could rip wheat seed into the soil condition of clean seed bed without straw and stubble mulching by high pressure accelerating airflow. During the pneumatic seeding experiment, keeping a certain pneumatic seeding height HG and incident angle α between the accelerating tube and topsoil surface, high-pressure gas was injected from the upper apex of the air nozzle and ejected from the bottom of it, which a stable high-speed airflow was formed in the accelerator tube (the length of the accelerator tube is 600 mm and the diameter is 10 mm). Then wheat seeds were put into the seed entrance and absorbed at a high speed under the negative air pressure of the ejector, during which the rubber sleeve could protect wheat seeds from damaging. After mixing with airflow, wheat seeds were accelerated by high-speed air flow in the accelerating tube. Finally, the wheat seeds flew out and ripped into the soil at a certain incident angle and high pneumatic seeding velocity. At the same time, high-speed photography technology was used to study the parameters of pneumatic seeding velocity, vertical velocity and pneumatic seeding depth under six levels (15°, 30°, 45°, 60°, 75°, 90°) of incident angles, and pneumatic seeding experiments under five different accelerating air pressures of 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa and 1 MPa for each incident angle were carried out respectively. Pneumatic seeding experimental results showed that: For pneumatic seeding in soil without straw and stubble mulching, when the incident angle increases continuously, wheat seeds can achieve higher vertical component of pneumatic seeding velocity deeper and pneumatic seeding depth at the same accelerating air pressures, the probability of horizontal slip and bounce of wheat seeds after touching soil show an decreasing trend, and pneumatic seeding depth has a positive correlation with pneumatic seeding velocity under each incident angle. Moreover, wheat seeds show various pneumatic seeding depth and soil impact effect without damage after pneumatic seeding. When the incident angles and the vertical component of pneumatic seeding velocity were more than 45° and 25 m/s respectively, wheat seeds can be completely ripped into the soil and the emergence rate is more than 86%. The best pneumatic seeding effect achieved as incident angle is 90°. In order to realize wheat vertical pneumatic seeding in field operation, the horizontal component of pneumatic seeding velocity should be equal to the operating speed of seeder and the vertical component of pneumatic seeding velocity should be greater than 25 m/s, which the seeder operating speed shows positively and negatively correlated with pneumatic seeding velocity and incident angle, respectively. The experimental results can provide basic data and technical support for the development of non-contact wheat seeding equipment in rice-wheat rotation area. [ABSTRACT FROM AUTHOR]

[Objective] The objective of this study was to understand the response of tobacco-planting soil pH and soil organic mailer to altitude and soil type. [Method] Statistical analysis was used to study the relationship between soil pH and soil organic matter of 251 soil samples which selected from 10 towns and villages in Mile city, and the relationship between altitude, soil type, and soil pH, soil organic matter were analyzed. [Result] the soil pH at tobacco-planting field in Mile city ranged from 4.39 to 8.45, and the average value was 6.51. The range of pH suitable for tobacco growth was 5.0-7.0 , which accounted for 56.67 % of soil samples. The pH value in paddy soil was significantly higher than that of clay soil, followed by red soil and sandy loam soil. The average value of soil organic matter was 30.60 g/kg, and the amplitude of variation was from 5. 02 to 64. 28 g/kg. Of 41.40 % soil organic matter was moderate, while 59. 80 % was abundant. However, the content of soil organic matter was not significantly affected by soil types (P>0.05), and showed sandy loam soil > red soil > clay soil > paddy soil. The elevation range of Mile tobacco area was from 1 135 m to 2124 m, and the soil pH presented a trend of ‘M’ type with the increasing elevation, while the soil organic matter presented a trend of ‘ W’ type. There was a negative correlation between soil pH and soil organic matter. [Conclusion]In most areas of Mile city, the soil pH was suitable, and the content of organic matter was high, which was suitable for tobacco planting. [ABSTRACT FROM AUTHOR]

In order to study how shear strength and its change in unsaturated soils modified by hydrophobic agent, sandy soils hydrophobized by dimethyldichlorosilane (DMDCS) were prepared. The hydrophobic soils with different DMDCS volume by soil mass, water content and clay content were obtained respectively. Mixtures of sandy soils (DMDCS volume by soil mass were 2 mL:100 g and 3 mL:100 g, i.e., 2% and 3%, the same below) with 3%, 5%, 7%, 11% and 13% water content were prepared respectively. Meanwhile, the mixtures of clay and sandy soils (3% DMDCS) according to the clay mass fraction of 0, 5%, 10%, 15%, 20%, 25%, 30%, 40% and 50% were prepared respectively. Then the unsaturated direct shear tests were carried out by unsaturated direct shear apparatus. Four samples in each group were prepared under the normal pressure in 100, 200, 300 and 400 kPa, respectively. The horizontal shearing ratio was 0.8 mm/min and the shearing test lasted 6 min. The results showed that: 1) The mixtures of sandy soils and DMDCS presented extreme hydrophobicity. 2) The water repelling of mixtures of clay and sandy soils was affected by both DMDCS and clay content. The water repelling of mixtures was degraded with the increasing of clay content, and improved with the increasing of DMDCS volume by soil mass. 3) The Mohr-Coulomb strength criterion could be adopted to describe the shear strength of hydrophobic sandy soils with different DMDCS and water content. With the increasing of DMDCS volume by soil mass, the shear strength index of the hydrophobic soil was decreased to different extents. The cohesive force showed a steep-drop shape from soil without DMDCS addition to that with 1% DMDCS and a slow decline up to stabilize finally. The effect of DMDCS on the cohesive force of modified sandy soils was much greater than on the internal friction angle. The hydrophobic soils’ cohesion with the increasing of water content was decreased gradually, while the internal friction angle was increased firstly and decreased finally. The water content had a much effect on the shear strength of the hydrophobic sandy soils. The shear strength index were decreased with the increasing of DMDCS volume by soil mass: the cohesion was declined rapidly from 19.6 kPa (no DMDCS) to 10.4 kPa (1% DMDCS) and slowly from 10.4 kPa (1% DMDCS) to 9.3 kPa (3% DMDCS). The internal friction angle was declined slowly from 16.2° (no DMDCS) to 11.8° (3% DMDCS). The cohesion was decreased with the increasing of water content: the cohesion was declined from 15.5 kPa (3% water content) to 7.5 kPa (13% water content) with 2% DMDCS and from 15 kPa (3% water content) to 5.2 kPa (13% water content) with 3% DMDCS respectively; the internal friction angle was increased from 12.7° (3% water content) to 15.2° (11% water content) with 2% DMDCS and from 11.7° (3% water content) to 14.6° (7% water content) with 3% DMDCS, then decreased to 13.9° (13% water content) with 2% DMDCS and 11.9° (13% water content) with 3% DMDCS respectively. 4) The Mohr-Coulomb strength criterion could also be adopted to describe the shear strength of hydrophobic mixed soils with different clay content. The cohesion was increased remarkably with the increasing of clay content. The cohesion of sandy soils without clay was 9.3 kPa, then suddenly increased to 27.2 kPa and 55.1 kPa mixed with 5% and 50% clay mass fraction, respectively. The internal friction angle was increased from 12.1° (5% clay mass fraction) to 16.2° (15% clay mass fraction), and then decreased to 9.7° (50% clay mass fraction). All the analysis could be beneficial to analyze the shear strength of hydrophobized soils and apply in engineering. [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]