Abstract:Soil structure is the foundation of soil function, which not only affects the processes of soil nutrient supply, water retention and infiltration, gas exchange, but also provides the physical habitats for soil microorganisms and regulates the key process of organic carbon turnover. The pore characteristics of soil can directly and truthfully reflect the quality of soil structure, and they can better reflect the regulating effect of soil structure on these processes. On this basis, quantitative analysis of the highly heterogeneous soil pore structure and the changes of soil microenvironment and the turnover process of soil organic carbon is essential to further understand the function of soil structure in soil ecosystem. Therefore, this paper focuses on the influence of soil pore structure on soil microenvironment and its relationship with organic carbon, analyzes the response process of soil microenvironment under the regulation of soil pore structure, expounds the direct and indirect effects of soil pore structure on soil organic carbon turnover, emphasizes the important role of soil pore in regulating soil organic carbon turnover process. Finally this paper prospects the research on soil pore structure in regulating the soil organic carbon cycle, the decomposition of plant residues and its coordination with microorganisms and so on.

Abstract:A field erosion simulation experiment was carried out to study overland flow soil erosion process under 2 terrace types (soil, stone), 3 terrace ridges (1, 2, 3 ridge), 1 slope gradients (10°), and 3 water flow rates (0.5, 1, 1.5 m³/h). The hydrodynamic characteristics of soil erosion in overland flow under terraced field measure were analyzed. The results showed that the terrace ridge had a great influence on the flow state of the overland flow. The Increasing in the number of terraces could reduce the fluctuation of the overland flow. The influence of terrace types on the Reynolds number was relatively small. The overall soil detachment rates increased with the increase of flow rates. Under the same flow conditions, the soil detachment rates increased first and then decreased, and gradually stabilized. The correlation between the two was fitted by exponential function regression equation (R²>0.840). For the similar terrace type and field width, and under the same conditions, the soil separation rates were negatively correlated with the number of the field, and the drag coefficient was negatively correlated with the flow. The soil separation rates and the drag coefficient were negatively correlated. The research results could be great significance for understanding the process and law of soil erosion on overland flow, and also provide reference for the establishment of physical model of overland erosion.

Abstract:Under natural rainfall conditions, the variations of runoff and sediment yield of typical native plant Rosa roxburghii quantitative studied on karst rocky desertification area of Northwest Guizhou, and the hydrodynamic mechanism of controlling erosion and sediment yield by hedgerow analyzed. The results showed that the interception and diversion of R. roxburghii hedgerow delayed runoff production and confluence time, increased runoff infiltration on karst slopes and reduced erosion power. Under different rainfall intensities, the infiltration rate of karst slope was negatively linearly correlated with runoff and sediment yield. The root system of plants twisted and banded the root soil in series, which changed the infiltration characteristics of the soil and enhanced the erosion resistance and corrosion resistance of the soil. Root density decreased with the increasing of soil depth and sediment reduction effect is also reduced. The soil erosion resistance was significantly positively correlated with the density of fibrous roots less than 1 mm, and linearly correlated with the quantity and length of fibrous roots less than 2 mm and the soil erosion resistance index. When the rainfall intensity of I₃₀ was 2.41 mm, there was almost no runoff erosion in hedgerow plot, but more sediment was produced in the control plot. When I₃₀ was 4.72 mm and 8.35 mm, the erosion and sediment yield of the study plots were all increased, and rills were formed in the control plot, which indicated that the rainfall intensity increased, the productivity of slope surface flow was strengthened, and the sand carrying capacity increased. It showed that hedgerows played an important role in water conservation, soil consolidation and sediment reduction, as well as in regulating the hydrodynamic process of soil erosion. The hydrodynamic forces of runoff erosion and sediment yield on karst slopes were mainly affected by rainfall intensity and kinetic energy of raindrops. The size of raindrop erosion depended on rainfall, rainfall intensity and raindrop size. Erosion sediment yield had a significant power function relationship with rainfall intensity and duration. It is reveals the regulation mechanisms of soil consolidation and sediment reduction by plant roots and the improvement of soil erosion resistance hydrodynamics.

Abstract:In the field plot experiment,four treatments, including CK (no fertilization+no straw), F (conventional fertilization), SF (straw incorporation+conventional fertilization) and SFR (straw incorporation+conventional fertilization reduced by 15%) were set up to study the effects of rice straw incorporation on nitrogen, phosphorus and chemical oxygen demand (COD) loss through runoff in rapeseed season under rice-rape rotation mode in Chaohu Lake region. The results showed that straw incorporation treatment significantly increased the number of soil microbial bacteria, fungi and actinomycetes, significantly reduced the total nitrogen concentration in runoff, but increased the total phosphorus and COD contents. The number of soil microorganisms was positively correlated with the content of nitrogen, phosphorus and COD in runoff. Compared with F treatment, total nitrogen loss decreased by 16.9%~19.8% and 27.1%~29.3%, total phosphorus loss decreased by 2.4%~4.0% and 4.0%~5.6%in the SF treatment and SFR treatment, while the COD loss increased by 6.1%~10.0% and 2.8%~6.1%, respectively.The results provided a reference for revealing the mechanism of soil microbial biomass and the loss of nitrogen, phosphorus and COD in runoff, and provided a theoretical basis for the rational use of straw incorporation technology.

Abstract:In order to scientifically understand the effect of the construction of check dam system on the erosion dynamic process in small watershed on the Loess Plateau, the storm flood process in the Wangmaogou small watershed was simulated by coupling the distributed hydrological model MIKE SHE with the one-dimensional hydrodynamic model MIKE 11, and the erosion dynamic parameters of the different sections of the main ditch as well as the sediment reduction benefits of different combination of dam types were calculated. The results showed that:(1) The erosion dynamic distribution of the gullies in the small watershed was changed by dam construction, and the erosion dynamic parameters of gullies decreased the most after the dam system was completed. (2) The runoff erosion power varied greatly in the upper and middle reaches, while tended to be stable in the lower reaches, and the runoff erosion power in the lower reaches was obviously lower than that in the upper reaches. (3) The construction of check dam could effectively reduce the sediment transport in the watershed. When the key, medium and small dams were built separately, the sediment transport modules were reduced by 24.74%, 47.11% and 64.11%, respectively, compared with those without dams in the watershed. After the completion of the dam system, the benefit of sediment reduction was the most obvious, and the sediment transport modulus was reduced by 83.92%. The research results were intended to provide scientific reference for evaluating sand reduction benefits of check dam on the Loess Plateau.

Abstract:In order to study the characteristics of typical soil splash erosion on slope farmland in low mountain and hilly region of western Liaoning Province, taking cinnamon soil as research object, the effects of rainfall characteristics and slope on splash erosion were studied by artificial rainfall simulation experiments. The results showed that with the increase of rainfall intensities, the splash erosion of 5° and 10° increased from 6.86 g/cm and 8.13 g/cm to 14.21 g/cm and 16.00 g/cm, respectively, with an increase range of 48.47% to 209.81%. The splash erosion with different splash distance was 0~5 cm > 5~10 cm > 10~15 cm > 15~20 cm > 20~25 cm. The splash erosion with splash distance at 0~5 cm with 75 mm/h was 7.29 g/cm, accounting for 45.56% of the total splash erosion (16.00 g/cm) in the range of 0~25 cm, and splash erosion with splash distance at 20~25 cm was only 9.88%. The splash erosion had a good exponential relationship with rainfall intensity and splash distance, and the determinant coefficient of the regression equation was above 0.8. With the extension of rainfall time, the splash erosion increased gradually, while the growth rate of splash erosion decreased. The growth rate of splash erosion was the largest when the rainfall duration increased from 5 min to 10 min. The splash erosion had a good exponential relationship with rainfall duration, and the determinant coefficient of the regression equation was above 0.9. Spatial distribution of splash aggregates changed with the changes of rainfall intensities. The splash distance of each diameter aggregate increased with the increasing rainfall intensities. The splash distance of 2~5 mm aggregate increased from 0~5 cm at 30 mm/h to 0~15 cm at 75 mm/h. Splash distance and splash erosion of small size aggregates were larger than that of large size aggregates. Splash aggregates were dominated by <1 mm aggregate, and >5 mm aggregate did not migrate. The total splash erosion, upslope erosion, downslope erosion, and net splash erosion of 5° with 75 mm/h were 14.21, 3.54, 10.67, and 7.13 g/cm, respectively, and which of 10° were 16.00, 3.85, 12.15, and 8.30 g/cm. Compared with 5°, the splash erosion of 10° increased by 12.60%, 8.76%, 13.87% and 16.41% respectively. The splash erosion on downslope was larger than that of upslope splash erosion.

Abstract:Based on field observations of runoff and sediments of water and soil erosion under different land uses generated on runoff plots and rainfall data from 2015 to 2017,we studied quantitatively the effects in upper area of Fen River. The results showed that:(1) The distribution of erosion rainfall in the study area was very uneven within a year and between years. Several times of heavy rainfall contributed a lot to the erosion of rainfall. (2) Under different rainfall conditions, the runoff or sediment holding capacity of the fish-scale pit + trees or shrubs was the strongest, while the bare land was the weakest. The runoff yield on slope was as follows:bare land > slope farmland > grassland > Pinus tabuliformis Carrière > Rosa xanthina Lindl. > fish-scale pit and Pinus tabuliformis Carrière > fish-scale pit and Rosa xanthina Lindl.. The slope sediment yield was:fish-scale pit and trees or shrubs < grass < trees or shrubs < slope farmland < bare land. (3) With the increase of rainfall, both the runoff regulation rate and sediment regulation rate of each vegetation plot showed a downward trend. With the increase of rainfall intensities, both regulation rates decreased obviously. (4) There were significant positive correlations between rainfall and runoff yield, runoff yield and sediment yield in each plot (P<0.05). There was no significant correlation between I₃₀ and runoff yield in bare land, Rosa xanthina Lindl. and grassland. There was no significant correlation between I₃₀ and sediment yield in bare land, Pinus tabuliformis Carrière, Rosa xanthina Lindl., and slope farmland.

Abstract:The applicability of the Curve Number Method (SCS-CN) in different land use patterns was discussed to provide some references for the evaluation of water and soil conservation measures by this method. Based on the monitoring data of runoff plots in semi-arid areas of Northeast China, the feasibility of SCS-CN method in evaluating soil and water conservation measures and tillage methods was analyzed by the methods of simultaneously calibrating of runoff curve number (CN) and the initial loss ratio. The results showed that:(1) Under the drought (AMC1) condition, the optimal value of λ was 0.05, but the simulation results of different land use patterns was not ideal, while the results of bare land, contour ridge and ridge along slope simulated by the modified method of the potential maximum retention (S) were better, and the corresponding CN₁ values were 87.54, 68.49 and 60.46, respectively, and the optimal value of λ was 0.40. (2) The results of horizontal troughs, vegetation belts and terraces were not ideal, and the calculated values were too large when the measured runoff was more than 10 mm. The simulation accuracy was greatly improved through correcting by runoff coefficient ratio, which was recommended as a suitable correction method for water conservation measures. (3) Under normal (AMC2) and wet (AMC3) conditions, the amount of data was limited, keeping the optimum value of λ remained, correcting S value, the simulation result was ideal, and it was a suitable estimation method for arid areas.

Abstract:In order to study the effects of different forest and grass restoration models on soil and water conservation on the hill slope in Karst trough-valley areas, the physical and chemical properties and infiltration characteristics of soils under different forest and grass patterns (forest land, pepper land and shrub grassland) on the consequent and reverse hill slopes in Karst trough-valley area were compared and analyzed by field investigation and indoor analysis. The results showed that:(1) The bulk density of forest land was the smallest, and the porosity, soil moisture content and organic matter content were the highest, followed by pepper land and shrub grassland. The soil organic matter content of the consequent hill slope was significantly higher than that of the reverse hill slope (P<0.05), but there was no significant difference in other physical and chemical indexes (P>0.05).(2) The infiltration curve of pepper land was steeper both on the consequent and reverse hill slopes, while that of forest land and shrub grassland were relatively slow. The infiltration rate of shrub grassland tended to be stable earlier (about 20 minutes), while the infiltration rate of pepper land and forest land began to decline slowly in about 30 minutes, and became gradually stable after 75 minutes. The soil infiltration capacity of forest and restoration modes on the consequent and reverse slopes was forest land > pepper land > shrub grassland(P<0.05). (3) In the infiltration model, Horton model had the best fitting effect (R²>0.712), compared with Kostiakov and Philip models. The determining coefficient R² of the regression equation between simulated stable infiltration rate and measured value was as high as 0.978 9.(4) The soil stable infiltration rate in the study area was positively correlated with total porosity, non-capillary porosity, saturated water content and pH value, but was negatively correlated with organic matter. Total porosity had the greatest impact on soil infiltration performance, while organic matter had the least impact. The multiple linear regression equation established by the above indexes could accurately predict the stable infiltration rate of soil. The results could provide a theoretical reference for the selection of vegetation restoration and the assessment of soil infiltration performance on the slopes of Karst trough-valley areas.

Abstract:To investigate the impacts of typical herbaceous plants roots on soil resistance to runoff erosion in the reservoir riparian zone, simulation flume experiments of undisturbed-soil were carried out to study the soil erosion resistance of 0-20 cm soil layers of three grasslands (Cynodon dactylon, Hemarthria compressa and Xanthium sibiricum), and the bare land was taken as CK, and the root characteristics of different herbaceous plants and their effects on soil erosion resistance were also discussed. The results indicated that:(1) The roots of the three herbaceous plants mainly distributed in 0-10 cm soil layer, root weight density, root length density, root surface area density and root volume density of H. compressa were significantly higher than those of C. dactylon and X. sibiricum (P<0.05). (2) With the prolonging of scouring time, the runoff sediment concentration of all soil samples decreased sharply at first and then gradually stabilized. The sediment concentration was higher and decreased rapidly within 0~3 min after discharge, decreased slowly within 3~6 min and stabilized within 6~10 min. Compared with the CK, the runoff sediment content could be effectively reduced in the different grasslands in the 10-minute scouring process. The runoff sediment concentration of 0-10 cm soil layer followed the order of CK > C. dactylon > X. sibiricum > H. compressa, while that of 10-20 cm soil layer followed the order of CK > C. dactylon > H. compressa > X. sibiricum. (3) During the scouring process, the index of soil anti-scourability increased slowly at first and then increased rapidly, it was small and increased slowly within 0~3 min, gradually increased within 3~6 min and rapidly increased within 6~10 min. Compared with the CK, the root systems of different herbaceous plants could effectively increase the soil anti-scourindex, while there was a significantly difference between the three grasslands and the CK in 0-10 cm soil layer. The index of soil anti-scourability of H. compressa grassland was the largest, which was 2.15 times of the CK, followed by X. sibiricum and C. dactylon grasslands, which were 1.60 times and 1.43 times of the CK, respectively. Furthermore, there also was a significantly difference in the index of soil anti-scourability between the grasslands and the CK in 10-20 cm soil layer besides the C. dactylon grassland. (4) The enhancement effects of herbaceous roots on soil anti-scourability mainly occurred in 0-10 cm soil layer, and the enhancement effects of H. compressa roots on soil anti-scourability was the largest, followed by X. sibiricum and C. dactylon. The soil anti-scourability was closely related to root distribution and morphological indexes, especially root surface area density and root volume density of roots with diameter (D) ≤ 1.5 mm.

Abstract:Accurate measurement of flow velocity of shallow water on slope is essential to analyze hydraulic parameters and establish soil erosion model. A flume of 12 m long, 0.1 m wide and 0.3 m height was used to measure the velocity of shallow water under five slope gradients (5°, 10°, 15°, 20° and 25°) and four flow discharges (2, 4, 8 and 16 L/min). By recording the time of flow front (front) passing through the flume, the leading edge velocity of flow was calculated. The average surface velocity and average velocity were measured by the dye tracer method and the electrolyte tracer pulse method, and compared with the leading edge velocity. The results showed that the leading edge velocity varied from 0.237 m/s to 1.290 m/s, and it increased with the increasing of flow discharge and slope gradient. The leading edge velocity was more sensitive to flow discharge than to slope gradient. The leading edge velocity could be predicted using a power function of slope gradient and flow discharge. By comparing the leading edge velocity with the average surface velocity measured by the dye tracer method and the average velocity measured by the electrolyte tracer pulse method, the results indicated that the leading edge velocity showed good consistency with the average surface velocity and the average velocity, but the average surface velocity was much larger than the leading edge velocity, and the relative error was -15.018% to -27.825%, and the conversion coefficient between the two velocities was 0.758. The leading edge velocity was relatively close to the average velocity, and the relative error decreased with the increasing of flow discharge and slop gradient, and the conversion coefficient between the two velocities was 0.946. The correction factor was more sensitive to Reynolds number than to flow discharge and slope gradient. The equations established in this study could be used to predict the correction factors. In general, the results of this study could be used as a reference to study the flow velocity of shallow water.

Abstract:In order to explore the influence of gravel content on rill erosion of colluvial deposit slope, the combination souring tests were conducted. This paper studied the morphological characteristics of rill cross section during scouring of four kinds of soil-rock mixed colluvial (gravel mass ratios of 0, 10%, 30% and 50%, respectively) with different scouring flow rates (2, 4, 8 and 12 L/min, respectively) under slope gradient of 30°. The results showed that:(1) With the increase of scouring time, the increasing speed of depth was greater than that of width, which made the shape of rill cross section develop toward narrow and deep. (2) The depth of rill cross section was large on the top of slope, which was similar to the "V" shape, and the erosion was severe. The depth of rill cross section was small on the bottom of slope and the erosion was relatively mild. The morphological index η of rill cross section fluctuated as the increase of slope length. (3) With the increase of gravel contents, the depth of cross section decreased first and then increased. The depth of rill was shallowest on the slope with 10% gravel content. The morphological variability of cross section was maximum on the slope with 10% gravel content. The free surface began to develop at the depth of 10~15 cm, and the soil with low gravel content was more conducive to the development of the free surface.

Abstract:In order to study the effects of slope gradient on sediment yield by ephemeral gully erosion on slope surface, taking the ephemeral gullies on the hilly and gully slopes of the Loess Plateau as the research object, four slope gradients including 14.0°, 18.5°, 26.0° and 29.0°, and five discharge flows of 5, 10, 15, 20, 25 L/min, were selected to study the effects of slope gradients on runoff rate, sediment yield rate, sediment concentration and total runoff and total sediment yield. The results showed that the slope gradients were positively correlated with runoff rate and total runoff at 5, 10, 15, 20, 25 L/min, and the runoff rate and total runoff increased with the increase of slope. Under the different discharge flows and gradients, the sediment yield rate, sediment concentration and total sediment yield had the same trend over time:increasing first-reaching maximum-decreasing fluctuatingly-stabilizing finally. The relationship between sediment yield rate, sediment concentration, total sediment yield and slope gradient:sediment yield rate, sediment concentration and total sediment yield increased first and then decreased with the increasing slope gradients, and the maximum value appeared at 26.0°. The sediment yield rate, sediment concentration and total sediment yield at 26.0° were 1.06~2.87 times, 1.31~2.21 times and 1.08~2.77 times of those at 14.0°, respectively. There were critical gradients for sediment yield rate, sediment concentration and total sediment yield, which ranged from 18.5° to 29.0°.

Abstract:In order to study the effects of hedgerow width on runoff and sediment yield process of purple soil slope and explore the critical hedgerow width for effective control of soil erosion, three hedgerow with different width (20, 30, 40 cm) were set up to analyze the runoff and sediment yield of purple soil slope land under different rainfall intensities (30, 60, 90 mm/h). The results showed that:(1) Hedgerow could effectively delay runoff generation time on purple soil slope, and the relationship between the runoff yield and the hedgerow width could be fitted into a quadratic equation (R²=0.99). With the increase of hedgerow width, the flow rate decreased, and the flow rate inside the hedgerow decreased most obviously, and the fluctuation range of the flow rate curve decreased. (2) Hedgerow could effectively restrain the increase of sediment yield on the slope in the early stage of sediment yield process, and the sediment yield on the slope decreased with the increase of hedgerow width. When the rainfall intensity was 30 mm/h and 90 mm/h, the R² of quadratic equation between the sediment yield and the hedgerow width was 0.99. (3) The hedgerow width caused an extremely significant effect on runoff and sediment yield. Under 30 mm/h rainfall intensity, the hedgerow with a width of 30 cm could achieve a remarkable benefit of reducing runoff and sediment yield.

Abstract:We performed a field plot experiment (2015-2016) to study the effects of different fertilization modes on phosphorus (P) losses by surface runoff, the apparent P balance, and vegetable and rice yield in a vegetable-rice rotation field in Taihu Lake Basin, China under natural rainfall conditions. The results showed that surface runoff events were mainly distributed in the rice growing season with heavy rainfall (rainy and typhoon season), which showed a significant positive linear correlation between the quantity of surface runoff water and rainfall capacity. And, phosphorus (TP) loss by surface runoff was also mainly distributed in the rice growing season, which accounted for 74.75%~81.46% of TP loss during the whole monitoring period including the vegetable and rice growing seasons. In T1 (conventional fertilizer application), the average TP concentration of surface runoff water in the vegetable growing season (0.55 mg/L) was significantly higher than that of rice growing season (0.29 mg/L), but TP loss (0.49 kg/hm²) was significantly lower than that of rice growing season (2.13 kg/hm²). Compared with T1, T2 (reducing application 31.17% of P compared with T1) and T3 (reducing application 49.75% of P compared with T1, in which, no P application during the rice growing season, and wheat straw biochar application during the vegetable growing season) could significantly reduce TP losses by surface runoff by 22.48% and 45.66% during the whole monitoring period, respectively. Furthermore, P surplus reached up to 260.90 kg/hm², which showed significant fertilization mode dependence and growing season dependence. In which, P surplus mainly occurred in the vegetable growing season, which accounted for 70.63% of that in the whole monitoring period. Compared with T1, P surplus in T2 and T3 decreased significantly by 38.47% and 64.87%, respectively. Moreover, compared with T1, vegetable yield decreased significantly under T2 and/or T3, but no significant difference was found between T2 and T3 in vegetable yield, rice grain yield, and annual yield of vegetable and rice grain. These results suggested that no P application during rice growing season and appropriate wheat straw biochar application during the vegetable growing season had synergistic effect of phosphorus reduction, maintaining stable crop yield and apparent P balance in the vegetable-rice rotation field.

Abstract:Wind erosion is a serious problem in agricultural regions of Northeastern China,where a north continental monsoon climate is prevalent and land is prepared for seeding using conventional cultivation ways such as ridge tillage or no tillage method. Affected by wind erosion, many studies reported the effect of tillage methods and coverage types on soil wind erosion,and pointed out that soil fine particles and nutrients (i.e., nitrogen and phosphorus) of top soil lose seriously by wind erosion, which have negative impacts on agricultural production and environment. Generally, wind erosion was affected by wind speed,soil water content,soil texture,and even the land cover types (like standing residues and flat residues) after harvest during wind season. Moreover, conservation tillage like no tillage or residue cover, could reduce soil wind erosion effectively on farmland. However, differences between black soil and aeolian sandy soil with different tillage and cover methods, especially in soil particles distribution and nutrient contents of wind erosion sediments, were unknown. Field experiments were conducted with ridge tillage and no tillage on farmland of three typical cover methods (no residue cover, remain standing residues and flat residues) on black soil and aeolian sandy soil in Northeastern China from April to June in 2016 and 2017. The soil particle distribution, organic matter, total nitrogen and phosphorus of wind erosion sediments were measured. Our results showed that the amount of wind erosion significantly decreased with increasing height; it was the highest at 0-10 cm and accounted for more than 50%, while it was closed to zero above 40 cm. The sediments from black soil were significantly lower than that from sandy soil. Furthermore, the amount of wind erosion of aeolian sandy soil was 168 folds than that in black soil at 0-100 cm in the same farming methods. In terms of tillage methods, the amount of sediments of no tillage were reduced by 66.0% to 94.1% as compared with ridge tillage, which indicated that no tillage could greatly decrease wind erosion. Apart from tillage types, flat residues can also reduce wind erosion obviously. Compared with no flat residues, the amount of sediment was reduced more than 90.3% by remain standing residues and flat residues during the spring. Affected by the wind erosion, the organic matter content of sediments was increased by 73.3%~85.8%, and even the soil particle distribution and nutrients of sediments lose seriously. The results of model analysis with RWEQ were verified by the results of our experiments, and the wind erosion modulus of RTNF (ridge tillage with no flat residues) was 181.7 to 86 582.9 t/(km²·a),however it was only 9.89 t/(km²·a) in NTF treatment (no tillage with flat residues). Our experiments indicated that remained stubble and residue cover management were effective ways to prevent soil wind erosion, while the ridge tillage and no residues can result in severe erosion and nutrients. It is, therefore, essential to pay high attention to the ridge tillage and no cover cultivate methods and adjust tillage and cover methods in Northeastern China.

Abstract:Topography attributes are the most important factors in controlling the initiation, evolution, distribution and damage of the gravity erosions triggered by rainfall. Based on the existing references and survey data, the revised increase-rate-analysis method, Arc GIS and Remote Sensing were used to evaluate the sensitivity of the gravity erosion to the topography factors in the Baota District, Yan'an City. The results showed that:(1) The slope gradient was the most important influential variable. The total amount of the gravity erosion, the amount of landslide and the amount of avalanche were all positively correlated with the gradients and their sensitivity parameters on the slopes were 60.5, 1 616.6 and 89.3, respectively. (2) For the total amount of gravity erosion and the amount of landslide, the distance to streams and the altitude were the second important factors. For the amount of avalanche, the vegetation cover and slope curvature were the second important factors. (3) The small-scale and medium-scale gravity erosion occurred frequently, and the large-scale gravity erosion had a low occurrence frequency, but the large-scale gravity erosion contributed more to the total amount of the gravity erosion. Among them, the events of large-scale gravity erosions with the amount greater than 100×10⁴ m³ only contributed 13% to the total frequency. Nevertheless, the contribution of the large-scale gravity erosions was up to 57% to the total amount of the failure masses. The results would provide a scientific basis for soil conservation and ecology restoration on the Loess Plateau, China.

Abstract:Forest litter plays an important role in controlling soil erosion on slopes, but its control mechanism remains to be clarified. In this study, the effects of different litter cover on runoff and sediment yield on slopes were investigated by laboratory large-scale soil trough and artificial simulated rainfall test. The experiment was conducted under four rainfall intensities (30,60,90,120 mm/h) and three litter mulching treatments (bare slope control, direct laying of litter and net laying of litter). Setting up the net laying of litter, which is in order to study on litter reducing splash erosion with reducing kinetic energy of raindrops. Setting up the direct laying of litter, which is in order to study on blocking interception of litter increasing ground roughness. The results indicated that:(1) The initial runoff generation time of slopes was prolonged by 2.3~5.5 times with the existence of litter, and the net laying of litter was longer than that of direct laying.(2)Compared with bare soil slope, litter decreased the runoff velocity by 47.9%~62.3%, and the smaller the rainfall intensity, the more obvious the effect of litter on reducing the runoff velocity. (3) Litter significantly increases infiltration and decreases runoff, and the effect is more obvious when rainfall intensity is small. (4) litter can reduce runoff and sediment by more than 75%, and direct laying is more obvious, mainly because litter increases surface roughness and reduces flow velocity. This study provides a theoretical basis for the establishment of soil erosion model on vegetation slope, and provides a scientific basis for the construction of vegetation for soil erosion prevention and control.

Abstract:Soil water infiltration movement is an important part of the evaluation of surge-root irrigation efficiency. Based on the theory of saturated-unsaturated soil water movement, we simulated the soil water infiltration under surge-root irrigation with a double-point source by Hydrus-3D and compared the simulated results with the field measured data. At the same time, the typical peach trees were selected and the optimal arrangement parameters of the surge-root irrigation were predicated. The study results showed that all the correlation coefficients between the simulated and the measured values of the soil wetting front of the surge-root irrigation and soil water content after irrigation were always greater than the critical correlation coefficient, RMSE was less than 1.5 and 0.05, respectively, and the P values of T-test were greater than 0.05. It indicated that Hydrus-3D could be used for soil moisture migration simulation of surge-root irrigation with reclaimed water. Using the Hydrus-3D model, the results showed that the optimal depth was 35, 35, and 45 cm respectively for peach tree with 1-year, 5-year and 10-year old, and the corresponding spacing was 40, 50, and 40 cm respectively.

Abstract:There are many factors affecting the flocculation and sedimentation of fine sediments. The objective of this study was to explore the effect of potassium sulfate fertilizer on the sedimentation of the static Yellow River water. Taking potassium sulfate concentration and sediment particle size as parameters, five potassium sulfate concentrations and four particle size ranges (<100, 50~100, 34~50, and <34 μm) of Yellow River sediment were studied by pipette method. In the sedimentation process, the effects of different potassium sulfate concentrations on the flocculation of fine sediments were discussed. The results showed that the higher the concentrations of potassium sulfate were, the faster the sediment concentration decreased, the higher the sedimentation velocity was. The initial particle size was <100 μm, and when the concentrations of potassium sulfate were 0, 2.86, 7, 14 mmol/L, the sedimentation time was 30 min, the relative sediment concentrations were 35.35%, 30.75%, 27.02%, 14.00%, and the median sedimentation speed ω₅₀ was 1.55, 3.00, 3.91 and 4.93 cm/min, respectively. The smaller the initial sediment particle size was, the more obvious the promotion effect of potassium sulfate on flocculation sedimentation was. The sediment of <34 μm sediment was most affected by potassium sulfate. When the potassium sulfate concentration increased from 0 to 60 mmol/L, the median sedimentation velocity after flocculation with initial particle size <34 μm increased from 1.38 cm/min to 8.53 cm/min, increased by 518.12%, and the median sedimentation velocity after flocculation with initial particle size of 34~50 μm increased from 6.29 cm/min to 8.43 cm/min, with an increase of 34.02%. The median sedimentation velocity of sediment from 50 to 100 μm increased from 7.12 cm/min to 7.59 cm/min, with an increase of 6.60%.The smaller particle size of sediment and the greater concentration of potassium sulfate gave the greater influence on the median particle size after flocculation. When the concentrations of potassium sulfate increased from 0 to 60 mmol/L, there was no obvious rule between the concentrations of potassium sulfate and the median particle size after flocculation of sediment with initial particle size of 50~100 μm. There was no significant difference between different treatments. Potassium sulfate had no effect on the flocculation settling of sediment with this particle size. After flocculation, the median size of sediment with initial particle size of 34~50 μm increased from 38.8 μm to 41.0 μm, increasing by 5.76%. After flocculation, the median size of sediment with initial particle size <34 micron increased from 15.7 μm to 21.6 μm, increasing by 37.82%. After flocculation, the relative contents of small and medium-sized particles decreased, the relative contents of large-sized particles increased, and the maximum particle size increased. When the particle size of sediment was <34 μm, the concentration of potassium sulfate was 60 mmol/L, and the maximum particle size after flocculation was 200 μm.

Abstract:In order to reveal the effects of different reclamation years and fertilization measures on nitrogen transformation characteristics of reclaimed soils in coal mining subsidence areas, intermittent leaching and aerobic culture method, laboratory aerobic incubation method with constant temperature and controlled humidity, and nitrate loss method were used to study the regularities of soil mineralization, nitrification and denitrification in reclaimed soil for four years and eight years, respectively, under five fertilization measures. The results showed that as the increasing of reclamation years, both cumulative mineralized nitrogen (N_t) and potentially mineralizable nitrogen (N₀) increased, while mineralization rate (N_t/N) and the proportion of N₀ to total N (N₀/N) did not change significantly. Under different fertilization measures, the N_t, N₀, N_t/N and N₀/N of eight years reclaimed soil in MCFB treatment (application chemical fertilizer combined with biological organic fertilizer) increased by 65.22%,65.21%, 60.42% and 60.76%, respectively, compared with chemical fertilizer treatment (CF). The soil nitrification rate and the time needed to reach the maximum nitrification rate (T_max) were less affected by reclamation years, and nitrification rates of different fertilization treatments were all higher than that of CK treatment, but there was no significant difference between treatments. The maximum nitrification rate (V_max) increased with the increasing of reclamation years. Treatments of MCFB could improve V_max and T_max more effectively than other treatments in soils reclaimed for four and eight years. Nitrate loss and nitrate disappearance rate increased with the increasing of reclaimation years. After seven days of cultivation, in the reclaimed soil for four years, the nitrate loss was the highest in organic manure treatment(M), reaching 78.72%, and the nitrate disappearance rate was the lowest in MCFB treatment, which was consistent with CK. There was no significant difference in soil nitrogen denitrification among different treatments for soil reclaimed for eight years. The sequence of short-term nitrogen transformation intensity was nitrification>denitrification>mineralization. On the whole, fertilization had obvious improvement effect on nitrogen transformation characteristics in reclaimed soil, and chemical fertilizer combined with biological organic fertilizer was more conducive to the maintenance and improvement of soil available nitrogen and reduce nitrogen loss.

Abstract:In order to study the effects of different layered fertilization on nutrient transport, a soil column leaching experiment was conducted. Taking the mixed application (ploughing after fertilizer application) as control, and no fertilizer, common urea and controlled release urea were mixed with phosphorus and potassium fertilizer respectively. A layer (depth 5 cm), two layers (5, 10 cm), three layers (5, 10, 15 cm) were applied to study the total nutrient leaching and fertilizer nutrient leaching rate under different layered fertilization treatments. The results showed that the total amount of inorganic nitrogen leaching in the layered application of common fertilizer was significantly lower than the control, and the three-layer fertilization gave the lowest. The leaching of inorganic nitrogen was generally low in all layered fertilization treatments. The application of controlled release fertilizer did not reach a significant level compared with the control. All layered fertilization treatments had no significant effect on the total leaching of available phosphorus. Compared with the mixed application, and the total amount of available potassium leaching under controlled-release fertilizer layered fertilization was also the highest in the three-layer fertilization treatment. Different layered fertilizations showed a great difference in the leaching rate of fertilizer nutrient. The nitrogen leaching rate of common fertilizer application was 9.9%, and the leaching rates of common fertilizer under one layer, two layers and three layers application treatments were 6.31%. 4.91% and 2.7% respectivley, the leaching rates of layered fertilization treatments were significantly lower than that of mixed application. The leaching rate of controlled release fertilizer was 3.28%. The leaching rates of one layer, two layers and three layers applications of controlled release fertilizer were 1.48%, 2.00% and 2.63%, respectively, the leaching rate of layered fertilization treatments were lower than that of mixed application, but it did not reach a significant level. The loss rate of phosphate fertilizer treated by layered application of common fertilizer was between 0.03%~0.05%, and 0.07%~0.08% for the layered fertilization treatments, both of which did not reach the significant level. The leaching rate of mixed application of potassium fertilizer in the normal fertilizer layered fertilization treatment was 0.35%, and the leaching rates of one layer, two layers and three layers of fertilization treatments were 0.40%, 0.49% and 0.55%, respectively, among which, the leaching rate of three-layer treatment was significantly higher than the mixed application treatment. The leaching amount of controlled release fertilizer mixed with potassium treatment was 0.24%, and 0.20%, 0.27% and 0.37%, respectively for the one layer, two layers, three layers applicaiton treatments. The leaching rates of controlled release fertilizer under three layers application was significantly higher than that of mixed application. The pH of each treatment varied from 7.22 to 8.24. There was no significant difference in pH among treatments. The electrical conductivity decreased significantly with the leaching for all treatments. The electrical conductivity of the first leaching treatment was the same, i.e., 7 547.00~9 360.00 μS/cm for the common fertilizer, and 5 570.00~9 370.00 μS/cm for the controlled release fertilizer. The electrical conductivity decreased to 1 985.67~2 470.00 μS/cm and 1 804.67~2 576.67 μS/cm respectively at the fourth leaching time. In summary, the total leaching amount of inorganic nitrogen in the common urea layered fertilization was significantly lower than that of the mixed fertilizer, and the three-layer fertilization was the lowest. The inorganic nitrogen leaching amount of the controlled-release urea was lower than that of the mixed fertilizer, but the difference was not significant. The layered application had no significant effect on the total leaching amount of phosphorus; the total leaching amount of available potassium of the common fertilizer three-layer application was significantly higher than that of the mixed fertilizer treatment. With the increase of leaching times, the electrical conductivity of leachate decreased significantly for all treatments, but the pH increased with the different degrees.

Abstract:We studied the effects of different irrigation and fertilization treatments on the growth of Viciavillosa Rothvar (Vetch) and the effects of the green manure on the growth of later-maize yield and soil fertility through field experiments. The results showed that both irrigation and fertilization significantly promoted the growth of Vetch. In the green manure season, irrigation could significantly increase the biomass, root activity, nitrogen and phosphorus nutrients accumulation of Vetch, whether fertilized or not. The Vetch biomass, root activity, nitrogen and phosphorus nutrients accumulation of NPW (applying nitrogen, phosphorus fertilizer and irrigation in green manure season) and CKW (no fertilization in green manure season, only irrigation treatment) consistently increased by 34.58% and 56.10%, 26.49% and 37.92%, 43.47% and 146.89%, 103.84% and 113.94%, respectively, compared with the corresponding no irrigated treatment. The amount of nutrients returned from the residual Vetch were 125.32~274.49 kg/hm², which accounted for 26.95%~59.03% of the total nutrients of chemical fertilizer in maize season. Compared with CF treatment (winter idle land treatment), the green manure growing under different fertilization and irrigation treatments promoted maize yield and nutrients accumulation and increased soil nutrients, and among the treatments, the effect of NPW treatment was the best. Under the same annual nutrient condition, 15.56% of nitrogen or 50.00% of phosphorus fertilization in the maize season transferred forward to the green manure growing season, which could significantly increase the amount of green manure nutrient returned to the field, the maize yield (8.39%~31.19%) and nutrients accumulation (7.31%~29.20%). In conclusion, under the conditions of appropriate irrigation and fertilization, the biomass of Vetch increased significantly, which had consistent increased the yield and nutrients accumulation of later-maize. The results could provide data support and practical basis for the application of green manure infield managements and fertilizer reduction in China.

Abstract:The objective of this study was to select the optimum tillage pattern though studying the effect of the different tillage patterns on the soil nutrient and crop yield. The field experiment was conducted with split plot design with six treatments:two main treatments with rotary tillage and deep tillage in wheat season, combined with three subsidiary treatments with no-tillage sowing, subsoiling between the row and subsoiling in the row in maize season, including (1) rotary tillage + no-tillage sowing (RT-NT); (2) rotary tillage +subsoiling between the row (RT-SBR); (3) rotary tillage + subsoiling in the row (RT-SIR); (4) deep tillage + no-tillage sowing (DT-NT); (5) deep tillage + subsoiling between the row (DT-SBR); (6) deep tillage +subsoiling in the row (DT-SIR). The results showed that, all the soil nutrient contents decreased with soil depths in both wheat and maize seasons. In wheat season, the total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP) and nitrate nitrogen (NO₃^--N) contents under rotary tillage treatments were significantly higher than those under deep tillage treatments; while, the soil organic matter (SOM), TN, AN, AP, NO₃^--N, and ammonium nitrogen (NH₄⁺-N) contents in 30-40 cm was increased under deep tillage treatments. In maize season, the SOM content in 0-30 cm under DT-NT treatment was increased by 40.1%~64.3% compared with RT-NT treatment. The TN content in 0-30 cm was increased under RT-SBR and RT-SIR treatment, with the highest value of 1.4 g/kg in 0-10 cm under RT-SBR treatment. The AN content was increased by 15.0%~25.3% in 0-20 cm under RT-SIR treatment compared with RT-NT treatment. In 0-40 cm, the highest AP content was observed under DT-SBR treatment, and the highest available potassium (AK) content was under RT-SBR treatment. The NO₃^--N (8.5~30.4 mg/kg) and NH₄⁺-N (2.6~8.9 mg/kg) contents in 20-50 cm under DT-SIR treatment were significantly higher than the others. Compared with the wheat season, the SOM in 10-20 cm, AN, AP and AK in 0-50 cm, NO₃^--N and NH₄⁺-N in 40-50 cm were increased in maize season. In maize season, the ear length, 100-grain weight, harvest index and yield under DT-SBR and DT-SIR were significantly higher than the others, and the yield was increased by 6.4%~10.8% under DT-SBR and DT-SIR compared with RT-NT treatment. The fertilizer partial productivity and economic benefit was highest under DT-SIR treatment in maize season. In sum, the soil nutrient contents and crop yield were improved under the DT-SIR treatment, which was suggested as the optimum practice in this study.

Abstract:The effects of nitrogen fertilizer synergist on yield and quality of rice and nitrogen utilization in cold regions were studied in order to provide scientific basis for formulating rational nitrogen management measures and strategies of improving yield, quality and nitrogen use efficiency in paddy field. Field trials were conducted in Fangzheng county, Heilongjiang province in 2017 and 2018 to study the effects of nitrogen fertilizer combined with nitrification inhibitor and urease inhibitor on rice yield, quality, nitrogen utilization and transformation and economic benefits. The results showed that the treatment of N+NI+UI (applying urea combined with nitrification inhibitor CP and urease inhibitor NBPT) significantly increased rice yield, the rice grain, straw and total biomass increased by 6.4%, 4.9% and 5.8% in 2017, 8.8%, 7.2% and 8.2% in 2018, respectively, compared with nitrogen fertilizer treatment (N). Application of nitrogen fertilizer synergist could improve the milling quality, appearance quality and nutritional quality of rice in cold regions, promote the nitrogen absorption of rice and improve the utilization efficiency of nitrogen fertilizer. Compared with N treatment, N+NI+UI treatment increased the apparent nitrogen utilization rate, agronomic efficiency and partial nitrogen productivity of rice by 15.6%, 19.1% and 7.6%, respectively. The combined application of CP and NBPT showed obvious synergistic inhibition effect on nitrogen transformation, delayed and reduced the peak value of NH₄⁺-N content in soil, maintained the NH₄⁺-N content at a higher level at growth stage of rice and extended the nitrogen supply time. Application of nitrogen fertilizer synergist could increase rice in cold area by 2 499.08 yuan/hm². In conclusion, nitrogen fertilizer combined with nitrification inhibitor CP and urease inhibitor NBPT could prolong the nitrogen release cycle, promote nitrogen absorption, improve rice yield and quality, enhance nitrogen use efficiency and increase economic benefits of rice in cold regions.

Abstract:The effects of the fourth type of Schiff base complex urease inhibitors with different concentrations on rape growth and soil nitrogen transformation were studied to provide a basis for the promotion and application of such novel urease inhibitors in agriculture. The effects of new urease inhibitor (SU) and commercially available urease inhibitor acetohydroxamic acid (AHA) on the yield, quality, growth, nitrogen uptake and utilization of rapeseed and apparent nitrification rate of soil were compared through outdoor potting methods. The results showed that SU and AHA both could increase rapeseed yield and improve quality index and nutrient index of rapeseed, but SU had a better effect on increasing yield and nutrient efficiency of rapeseed than AHA. SU increased the yield of rapeseed by 28.0% on average, and significantly reduced the nitrate content by 28.8%~50.8%. At the same time, it promoted the absorption of nitrogen and phosphorus in rapeseed, the utilization rate of nitrogen fertilizer increased by about 68.0% on average, and also reduced the apparent nitrification rate of soil by about 35.2% on average. The novel inhibitors with different concentrations had different effects on the indicators of rapeseed and the inhibition of urea hydrolysis. The effects of low-medium concentration inhibitors on rapeseed yield increasing and nutrient efficiency were better than those of high concentration inhibitors, and the inhibitory effect of inhibitors on the urea hydrolysis was the best when the amount of inhibitor was 1% of pure nitrogen application, so the best amount of inhibitor was 1% of pure nitrogen.

Abstract:In order to explore the effects of different vegetation restoration models on carbon (C) nitrogen (N) phosphorus (P) content of soil and its ecological stoichiometry and provides a scientific basis for vegetation restoration measures and ecological management model optimization in red soil erosion areas. The severely degraded red soil in Tai he County of Jiangxi Province was taken as the research object, and we chose the water stable aggregate which in 0-20, 20-40 cm soil layer with five restoration patterns (Pinus massoniana Lamb. pure forest, Pinus elliottii pure forest, Schima superba Gardn. et Champ. pure forest, and mixed forest of Pinus massoniana Lamb. and Pinus elliottii) to explore it. The results show that:(1) The average content of water-stable aggregates of 0-40 cm was 56.34% (>2 mm), 30.01% (0.25~2 mm), 7.14% (0.053~0.25 mm), 6.54% (<0.053 mm), respectively. The content of soil water-stable aggregates decreased with the reduction of soil particle size, and the difference was significant (P<0.05). In mixed forest of Pinus massoniana Lamb.,>2 mm water-stable aggregates content was significantly higher than that in other recovery models (P<0.05); (2) The contents of C, N and P in the vegetation restoration model were higher in the mixed forest of Pinus massoniana Lamb. and pure forest of Pinus elliottii. The content of C, N and P in soil water-stable aggregates increased in totality with the decrease of particle size and the content of nutrients with smaller grain size was significantly higher (P<0.05); There are significant differences in the content of C, N and C:N, C:P, N:P in different soil layers, but no distinct difference in the content of P. There were significant differences of C:N, C:P and N:P among particle sizes. Soil aggregates C, N are significantly correlated with C:N, C:P, N:P, N:P value is high and there is a significant negative correlation with P (P<0.05); (3)Soil aggregates C and N were significantly correlated with soil C and N (P<0.05), soil bulk density and water content (P<0.01). Research indicates:The improvement of soil nutrients by different vegetation restoration models is mainly concentrated in the topsoil. Soil aggregates had an indicating effect on soil nutrient, which related with soil physical properties. The limiting factors of vegetation growth in the study area are mainly P-limited and the macroaggregates and microaggregates are more severely restricted by P, mixed forest of Pinus massoniana Lamb. have significant effects on soil quality and structural improvement compared to other vegetation restoration models.

Abstract:A field experiment was conducted using asparagus lettuce as test material to study the effects of different fertilizer combinations on dry matter accumulation, nutrients absorption, fertilizer use efficiency, soil physical-chemical properties and soil microbial quantity, which could provide the scientific basis for reasonable fertilization of asparagus lettuce. The experiment used a completely randomized block design to set a conventional fertilization (CF), reduction of 20% (F₁) and 30% (F₂) and combined with 3 000 kg/hm² (B₁) and 6 000 kg/hm² (B₂) bio-organic fertilizer. The results showed that compared with the CF, the accumulations of dry matter in roots, stems and leaves of F₁B₂ treatment were increased by 5.74%, 22.19% and 17.82%, respectively, and the accumulations of N, P and K nutrients were increased by 128.81%, 113.19% and 23.15%, respectively. The reduction of fertilizer combined with bio-organic fertilizer could significantly improve the fertilizer use efficiency, agronomic efficiency and partial factor productivity of N, P and K fertilizers. The soil N, P and K dependent rates of CF were the highest. The application of bio-organic fertilizer could significantly increase soil nutrients contents. Compared with CF, the contents of soil organic matter, total N, P, K and alkaline N, available P and available K were increased by 71.65%, 84.53%, 75.41%, 19.94%, 75.90%, 17.06% and 24.35% respectively in F₁B₂, and were increased by 58.51%, 70.17%, 72.13%, 9.28%, 42.94%, 13.48% and 11.42% respectively in F₂B₂. The combination of chemical fertilizer and bio-organic fertilizer could increase the number of bacteria and actinomycetes in the soil of asparagus lettuce, and inhibit the growth of fungi. Compared with CF, the number of aerobic azotobacter, anaerobic azotobacter, nitrifying bacteria and denitrifying bacteria were increased by 1.36, 6.10, 47.50 and 23.76 times, respectively in F₁B₂. The number of bacteria was significantly positively correlated with the contents of organic matter, alkaline N, available P and total N. There was a significant positive correlation between the number of actinomycetes and the contents of total P. The number of azotobacters and nitrogen transformational bacteria showed a significant or extremely significant positive correlation with the contents of alkaline N and total N. According to the principal component analysis and comprehensive scores, the soil quality under different fertilization treatments with the following sequence of F₁B₂, F₂B₂, F₁B₁, F₂B₁, CF and CK. The partial substitution of chemical fertilizer by bio-organic fertilizer could not only improve the amount of asparagus lettuce's nutrients accumulation and fertilizer use efficiency, but also significantly increase the contents of soil nutrients, regulate the structure of soil microbial community, and improve soil physical and chemical properties. In summary, the partial substitution of chemical fertilizer by bio-organic fertilizer had a good effect on the nutrients accumulation of asparagus lettuce, and could improve the fertilizer use efficiency and soil fertility. The F₁B₂was a good fertilization mode with a rational use of fertilizer resources and improved soil environment.

Abstract:In order to explore the influence of different vegetation restoration patterns on soil fertility in the coal mine dump of ecotone between agriculture and pasture, five vegetation types, Prunus armeniaca+Alfafa(A1), Poplar+Alfafa (A2), Poplar + Seabuckthorn (A3), Poplar +Elymus nutans+Alfafa (A4), Abandoned land (CK), were selected as research samples in Heidaigou Opencast Coal Mine. We mainly analyzed soil basic chemical properties, enzymes activities and microbial biomass with the method of their relations using correlation analysis and path analysis hoping to uncover the driving factors of the differences between soil microbial biomass under different vegetation restoration. The effect of different vegetation restoration on soil quality of Opencast Coal Mine was evaluated by soil reclaimation index (RI). The results showed that:(1) Compared with the abandoned land (CK), soil organic matter, alkali solution nitrogen content, soil microbial biomass and soil enzymes activities were significantly increased(p<0.05), but soil pH had no obvious change and no significant difference (p>0.05) under different vegetation restoration. Soil organic matter, alkali solution nitrogen content, soil microbial biomass and soil enzymes activities decreased from 0-10 cm to 10-20 cm soil layer. (2) The content of soil microbial biomass carbon and nitrogen were significantly correlated with enzymes activities and organic matter content. Soil microbial biomass carbon and nitrogen were sensitive to the changes of soil organic matter content and enzymes activities which could be used as microbial indicators for changes in soil quality. (3) The soil recovery index in 0-10 cm and 10-20 cm layers under different vegetation restoration were A3 > A2 > A4 > A1 and A3 > A2 > A1 > A4 respectively. Therefore, the reclamation mode of Poplar + Seabuckthorn (A3) and Poplar + alfalfa (A2) improved the soil quality of the coal mine dump.

Abstract:Taking rotary tillage combined with border irrigation as the control (CK), the effects of different tillage methods, including autumn subsoiling (QS35) and summer subsoiling (XS35) under border irrigation, and different irrigation methods, including autumn subsoiling with border irrigation (QS35), autumn subsoiling with microspray irrigation (QS35SI) and autumn subsoiling with drip irrigation (QS35DI), on photosynthetic characteristics of maize were studied to determine the rational irrigation methods under subsoiling. The results showed that the LAI, chlorophyll relative content, net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate and yield of QS35 were 20.7%, 6.4%, 17.8%, 36.9%, 40.1%, 18.9%, 9.6% higher than CK under different tillage modes, respectively. There were no significant differences in F_v/F_m before and after anthesis, the qP, ETR, Y(Ⅱ) before and after an thesis were QS35>XS35>CK, while NPQ was QS352 concentration, transpiration rate and yield of QS35 SI treatment were 23.8%, 11.2%, 37.9%, 69.1%, 79.2%, 38.7%, 7.5% higher than CK, respectively. There were no significant differences in F_v/F_m before and after flowering, the qP, ETR, Y(Ⅱ) before and after flowering were QS35 SI > QS35 DI > QS35 > CK, while NPQ was QS35 SI

Abstract:A two-years experiment was designed to examine effects of different nitrogen (N) reduction and controlled-release urea application ratio on spring maize yield, water use efficiency and nitrate-N residue, so as to provide a reasonable fertilization management model for the dryland farming systems on the Loess Plateau. The experiment was performed from April 2017 to September 2018 in the rain-fed agricultural area of the Loess Plateau. Spring maize was planted with half plastic film mulching in one crop per annum. The experiment included six treatments, CK (no nitrogen fertilization treatment), N1C1 (the treatment of 65% controlled-release urea and 35% urea, N 200 kg/hm²), N1C2 (the treatment of 50% controlled-release urea and 50% urea, N 200 kg/hm²), N1C3 (the treatment of 35% controlled-release urea and 65% urea, N 200 kg/hm²), N1 (reduce nitrogen fertilization mode, urea, N 200 kg/hm²), N2 (conventional nitrogen fertilization mode, urea, N 250 kg/hm²).The soil moisture content, the yield of spring maize and nitrate nitrogen content in soil profile (0-300 cm) at harvest period were measured. The results of two years experiment showed that compared with the N2 treatment, N1 treatment did not reduced the crop yield, but significantly increased the crop yield (p<0.05), which increased by 9.6% and 6.9% respectively and significantly increased the water use efficiency (p<0.05), by 13.3% and 10.2% respectively in 2017 and 2018. Under the same nitrogen application rate (200 kg/hm²), compared with N1, the treatment of applying a certain proportion of controlled-release fertilizer reduced the yield of spring maize and the water use efficiency in 2017; the treatment of N1C2 significantly increased the yield of spring maize and the water use efficiency (p<0.05) by 7.7% and 11.6%, respectively in 2018. In addition, after two years of experiment, the reducing nitrogen application and applying a certain proportion of controlled-release fertilizer could significantly reduce the amount of residual nitrate nitrogen in soil profile (0-300 cm) (p<0.05), the N1 treatment reduced by 61.2% compared with the N2 treatment. Under the same nitrogen application rate (200 kg/hm²), the N1C2 treatment reduced by 50.8% compared with the N1 treatment.

Abstract:To evaluate the effects of straw and lime application on soil micronutrients and tomato yield, soils from plots amended with no fertilizer (CK), chicken manure (M), chicken manure + straw (MR), chicken manure + lime (MCa), chicken manure + straw + lime (MRCa) were collected. The results showed that:(1) Straw increased the contents of DTPA-extractable Fe, Mn and Zn in soil, MR caused 3.2%, 80.9% and 15.1% increase compared with M, respectively. Lime increased the contents of DTPA-extractable Fe, Mn, Cu, Zn in soil. The DTPA-extractable Fe, Mn, Cu and Zn contents in soil were significantly correlated with soil pH values and organic matter contents (P<0.01). (2) The micronutrients decreased as the aggregate sizes decreased. Adding straw and lime increased the DTPA-extractable Mn content in soil aggregate of 1~0.25 mm, MRCa caused 6.6%~46.6% increase compared with other treatments. Straw increased the DTPA-extractable Zn content in the aggregate<0.25 mm. The DTPA-extractable Fe content in soil was positively correlated with that in aggregate of <1 mm (P<0.01), the DTPA-extractable Mn and Zn contents were positively correlated with those in all aggregates sizes (P<0.01), and the DTPA-extractable Cu content in soil was positively correlated with that in aggregate of 1~0.25 mm (P<0.01). (3) Straw or lime increased tomato yield, the MRCa treatment had the highest yield, which was 12.6%~151.1% higher than other treatments. The DTPA-extractable Fe and Cu contents in soil were positively correlated with yield. The DTPA-extractable Fe had a direct effect and it sdecision coefficient was the highest. The DTPA-extractable Cu had an indirect effect. Therefore, straw and lime could alleviate the shortage of micronutrients in greenhouse soil, and the maximum crop yield could be obtained, which guaranted the sustainable utilization of soil in greenhouse and the sustainable development of greenhouse agriculture.

Abstract:In order to study the suitable straw decomposition agents for different soil textures, six treatments were set up to determine the decomposition rate of maize straw, maize yield, characteristics of maize root system and soil chemical properties in the irrigation area of West Liaohe Plain from 2017 to 2018, in which maize straw mixed with Renyuan maturation agent and Zhongnong Lvkang maturation agent were returned to medium loam and sandy loam, and straw returning to the field without applying maturation agent was taken as the control. The results showed that there was no significant difference in the decomposing rate between the two kinds of maturation agents in different texture soils. The yield, root characteristics and soil chemical properties of the middle loam in the two years all followed the order of Renyuan maturation agent > Zhongnong Lvkang maturation agent > control, and the values of Zhongnong Lvkang maturation agent and Renyuan maturation agent were significantly higher than those of the control, while there was no significant difference between the two kinds of maturation agents. The yield, root characteristics and soil chemical properties of sandy loam in the two years all followed the order of Zhongnong Lvkang maturation agent > Renyuan maturation agent > control, and the values of Zhongnong Lvkang maturation agent were all significantly higher than those of Renyuan maturation agent and the control. For improvement of the root characteristics and soil chemical properties, in sandy loam soil, the effect of applying Zhongnong Lvkang maturation agent was better than that of Renyuan maturation agent, while in medium loam, there was no significant difference between the two kinds of maturation agents.

Abstract:In order to explore the effects of organic materials combined with rainwater collection measures (OMR) on soil physicochemical properties of apple orchard under rain-fed conditions on the Loess Plateau, apple orchards in Yan'an of Shaanxi Province were selected to conduct the experiments in April 2016. Fish scale pit and rain-collecting pit were conducted on the reverse slope of crown projection surface of apple trees, and the effects of different dosages of organic materials (5 250 kg/hm² (OMR1), 4 500 kg/hm² (OMR2), 3 750 kg/hm² (OMR3) and 0 kg/hm² (CK)) and traditional treatment (T) on soil physicochemical properties were studied. Soil water content and electrical conductivity in 0-300 cm soil layer, nitrate nitrogen content in 0-200 cm soil layer and soil bulk density and saturated hydraulic conductivity in 0-100 cm soil layer were determined. The results showed that OMR could significantly increase the soil moisture content in 0-300 cm soil layer, and the average soil moisture content increased most significantly in OMR2 treatment. The soil root wetting areas in OMR1, OMR2 and OMR3 treatment were mainly concentrated in 0-100 cm soil layer. In the 0-300 cm soil layer, the multiple average moisture content of OMR2 treatment was the highest (14.87%), while that of OMR1, OMR3, CK and T treatment was 14.74%, 14.80%, 12.79% and 8.66%, respectively. The OMR could significantly increase the content of nitrate nitrogen in 0-200 cm soil layer, especially in 40-100 cm soil layer. The OMR could significantly reduce soil bulk density, especially the bulk density of 20-60 cm soil layer. The OMR could increase soil saturated hydraulic conductivity, especially in 0-40 cm soil layer. The OMR could increase soil electrical conductivity, and the peak value appeared in 60-100 cm soil layer, and the electrical conductivity of 0-300 cm soil layer followed the order of OMR2 > OMR1 > OMR3 > CK > T. Overall, the OMR in Yan'an, Shaanxi could significantly improve soil moisture content, and nitrate nitrogen content, soil saturated hydraulic conductivity and electrical conductivity, reduce soil bulk density, with make fruit trees grow in suitable environment and promote sustainable development of local fruit industry.

Abstract:Global warming has become one of the most serious environmental problems to human beings, and soil is an important source of greenhouse gas emissions. The application of wheat straw and biochar to soil plays an important role in soil carbon and nitrogen conversion and micro-gas metabolism; however, few studies have focused on the soil microbial activity and soil greenhouse gas emission by the application of wheat straw and biochar. This study adopted an indoor culture experiment, using soil added by wheat straw and biochar, to explore the effects of wheat straw and biochar on soil greenhouse gas emission and soil microbial activity. Five treatments were set up, that is, soil (S), soil+1% wheat straw (WT), soil+1% biochar (BC1), soil+2% biochar (BC2), soil+4% biochar (BC4). The results showed that the addition of wheat straw significantly increased the amount of greenhouse gas emissions in the soil, the application of wheat straw presented a sizable contribution to the greenhouse effect according to the dynamics of global warming potential (GWP).With the increase of culture time, the addition of biochar showed a certain inhibitory effect on soil N₂O emission. The addition of wheat straw could promote the increase of soil microbial biomass carbon to a certain extent, and promote the activities of FDA hydrolysis, urease, catalase, and phosphatase. The soil catalase activity was significantly activated by the application of biochar after a certain period.

Abstract:In order to study the effects of Robinia pseudoacacia forestlands with different densities on soil moisture in the loess region of Western Shanxi Province, the R. pseudoacacia forestlands with densities of 2 400 per hacter and 1 300 per hacter were selected to represent the high and low density R. pseudoacacia forestlands in the study area respectively, and the bare land as a control. The soil water content in 0-150 cm range and precipitation outside the forest were carried out by using Enviro-SMART soil moisture positioning monitoring system and self-recording dump rain gauge. The results showed that:(1) In different precipitation years, the average soil water storage of low-density R. pseudoacacia forestland was higher than that of high-density R. pseudoacacia forestland in drought and normal years. In these years, the absolute value of annual average soil water storage of low-density R. pseudoacacia forestland was 6.80 mm higher than that of high-density R. pseudoacacia forestland. (2) In the vertical direction of soil profile, the water consumption of 0-30 cm soil layer by high-density R. pseudoacacia forestland was higher than that of low-density R. pseudoacacia forestland in drought and normal years, and there was no significant difference in soil moisture consumption between these two kinds of R. pseudoacacia forestlands in wet years(P>0.05). (3) Comprehensive analysis of rainfall infiltration depth, infiltration amount and compensation degree of soil moisture in rainy season, natural rainfall in the study area could effectively supplement the soil moisture consumed by low-density R. pseudoacacia stand growth, and there was no new ecological degradation caused by water shortage in the process of vegetation restoration in the Loess Plateau. However, considering the consumption of soil moisture by high density R. pseudoacacia forestland, it was suggested that low density R. pseudoacacia forestland should be popularized in vegetation construction in the study area.

Abstract:In order to analyze the temporal stability characteristics of soil moisture content in Eucalyptus forests, nine sample points on a typical eucalyptus forest slope were selected to measure the soil moisture content for five years. Based on the measured data, the temporal and spatial variability and temporal stability of soil water content were analyzed by relative difference method and Spearman rank correlation coefficient method. The results illustrated that the average surface soil moisture content of five years of the study slope area was 21.81%, which showed weak variability in space and moderate variability in time. The correlation coefficient of average soil moisture content was low in each year, and the spatial pattern of soil water content had weak similarity in observation time, and the variation range of the average relative difference was -7.08% to 5.03%, and the average values of relative difference standard deviation and time stability index were 5.73% and 6.58%, respectively, indicating that the soil moisture had better time stability under different slope conditions. The moisture content of measuring points 2, 3, 6, 7 and 8 were higher than the average value, while the moisture content of measuring points 1, 4, 9, and 5 were relatively low. The standard deviation and time stability index of the wetting point were relatively small and stable, indicating that the moisture stability of soil in the wet state was better than that in the dry state. According to the regression analysis, there was a high correlation between the soil moisture content of point 5 and the mean water content of the whole slope, with the R² value of 0.879, the MBE value of 0.141 and the RMSE value of 99.4%. In other words, point 5 could be used as a representative measurement point to estimate the average soil moisture content in the shallow layer of the whole research area.

Abstract:Taking Populus euphratica forests in extremely arid area as the research object, we studied the soil water movement and the ecological water consumption characteristics under different water conditions. The results showed that the HYDRUS-1D model had a good simulation effect on soil water movement and evapotranspiration in forestland in extremely arid regions. The soil water movement and ecological water consumption of Populus euphratica forests under different water conditions were significantly different. As the moisture condition of the underlying surface tended to be wet, the soil moisture content and the wetting front infiltration depth increased, and the infiltration depth reached 100 cm, 120 cm and 150 cm, respectively. The changes in moisture conditions on the underlying surface resulted in the changes in soil moisture storages. When the water supply of the underlying surface increased, the evapotranspiration of Populus euphratica forest increased significantly, and the transpiration increased significantly. The percentage of transpiration in the total evapotranspiration gradually increased from 55% to 65% as the moisture conditions became wet. Studies showed that with the gradual wetting of the underlying surface moisture conditions, the ecological water consumption of Populus euphratica forests in the extremely arid regions is gradually increasing, and transpiration is the main reason for the increase of water dissipation.

Abstract:Seven afforestation densities of Picea crassifolia plantations were taken as the study object in this article in Anmentan small watershed, Datong County, Qinghai Province. Flooding method and ring knife method were used to determine water holding capacity of litter, herbaceous layer and 0-60 cm soil layer. This study quantified water conservation functions of Picea crassifolia plantation with different densities. The results showed that:(1) The maximum water holding capacities of litter varied from 1.97 m³/hm² to 7.60 m³/hm² for different afforestation densities. The afforestation density with the maximum litter water holding capacity was 1 725 plants/hm², whereas the afforestation density of 2 300 plants/hm² gave the minimum. The variation range of water holding capacities of understory herbaceous layer with different afforestation densities was as followed:1.97~7.17 m³/hm². The maximum water holding capacity of understory herbaceous layer was 1 575 plants/hm². (2) The water conservation functions of 0-60 cm soil layer were closely related to soil physical properties, soil permeability and water storage. The variation range of soil bulk density was 1.20~1.43 g/cm³. The total porosity in soil varied from 46.53% to 53.30%. There was a negative correlation between soil bulk density and soil total porosity with afforestation density. The forest land with density of 1 575 plants/hm² had the smallest soil bulk density and maximum soil total porosity. The permeability of soil mainly depended on the non-capillary porosity of the soil. They had a significant correlation. The permeability of the soil with the density of 1 575 plants/hm² was the strongest, and the worst with the density of 2 300 plants/hm². The range of saturated water storage in 0-60 cm soil layer was between 2 792.50 to 3 197.90 m³/hm². The soil saturated water storage with afforestation density of 1 575 plants/hm² was the largest. (3) The water conservation functions were evaluated by using the total water storage of forest land. The order of total forest water storage was D₁₅₇₅(3 207.37 m³/hm²) > D₂₃₀₀(3 164.67 m³/hm²) > D₁₉₀₀(3 157.17 m³/hm²) > D₁₆₅₀(3 141.12 m³/hm²) > D₁₄₇₅(3 105.91 m³/hm²) > D₁₇₂₅(2 998.32 m³/hm²) > D₁₃₅₀(2 803.68 m³/hm²). This results matched with the local afforestation specifications of 2 m×3 m. These findings provides a theoretical basis for the sustainable management of Piceacrassifolia plantation in the high and cold region of Loess Plateau of Qinghai Province.

Abstract:Taking four types of water conservation forests at the Hunhe River source as the research object, the morphological characteristics and change regularity of soil preferential flow in different water conservation forests were studied by field dyeing tracer and indoor physicochemical analysis, to reveal the formation mechanism and influencing factors of preferential flow in the process of protection and management of water conservation forest. The results showed that the infiltration depth of the soil preferential flow ranged from 30 cm to 38 cm in the four plots, and its depth was closely related to root length density. The dyeing area ratios of soil preferential flows in 0 -10 cm soil layer were 82.41%, 75.44%, 91.03% and 79.82%, respectively, and the dyeing area ratio of soil preferential flow decreased with the increasing of soil depth, and the dyeing area ratio of upper soil was significantly larger than that of the lower soil in the four plots. The dyeing area ratio of soil preferential flow was significantly or positively correlated with soil bulk density, total porosity, organic matter and total root length density, which all affected the occurrence degree of preferential flow, and got the multi-function relationship between the soil preferential flow dyeing area ratio and the influence index. According to the score and weight of each principal component, the comprehensive scores of soil priority flow characteristics of water conservation forests were mixed forest land (3.134) > larch forest (1.660) > cutting area (-1.946) > Korean pine forest (-2.847). The results could provide scientific basis for further study on ecological hydrological process and vegetation construction of water conservation forest at Hunhe River source.

Abstract:Using the method of space instead of time, Pinus massoniana plantations of 8, 18, 26 and 36 years old were selected as the research objects on plateau mountains, central part of Guizhou Province, and the content of soil organ carbon (SOC), total nitrogen (TN) and total phosphorus (TP) were determined in the four plantations to analyze the variation law and stoichiometric characteristics of nutrient contents at different development stages. The results showed that the average value of SOC, TN and TP in four P. massoniana plantations at the different ages were 12.24 g/kg, 1.94 g/kg and 0.35 g/kg, respectively, and the average value of C:N, C:P and N:P were 6.58, 38.70 and 13.65, respectively. The average ecological stoichiometric ratio of C:N:P was 39:6:1. Generally, the soil nutrient was insufficient in the four P. massoniana plantations. Soil SOC and TN of the four plantations decreased with the increasing of soil layer depth, but C:N increased, while the change rule of TP, C:P and N:P was not obvious. With the increasing of plantations age, content of SOC and TN and N:P decreased first and then increased, and TP decreased persistently. Meanwhile, C:N significantly decreased in the 36-year-old plantation, but there was no significant difference in other plantations. There was no obvious change rule for C:P. The correlation analysis showed that soil SOC and TN were the main factors regulating the soil ecological stoichiometric ratio of P. massoniana plantations. These results could provide important reference for illuminating soil nutrient cycling of P. massoniana plantations in plateau mountains.

Abstract:Soil salinization is a serious threat to the sustainable development of turfgrass, and breeding and planting salt-tolerant turfgrass can improve and utilize large area of saline soil. The effects of NaHCO₃ stress at different concentrations (0, 0.2%, 0.4%, 0.6%, 0.8% and 1.0%) on the physiological and ecological characteristics of three types of cold-season turfgrass, including ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea L.) and kentucky bluegrass (Poa pratensis L.) were studied by pot experiment. The results showed that the turf quality, leaf wilting score, leaf relative water content, leaf chlorophyll content and K⁺ content of the three types of cold-season turfgrass decreased with the increasing of NaHCO₃ concentration, and the higher the concentration, the more obvious the decrease. Dry weight of aboveground and roots of the three types of cold-season turfgrass reduced under 0.4%~1.0% NaHCO₃ stress, and with the increasing of NaHCO₃ concentration, the inhibition degree of growth increased significantly, and the inhibition degree of root system was more obvious than that of aboveground parts. The leaf relative conductivity, proline content, malondialdehyde content and Na⁺ content showed an increasing trend with the increasing of NaHCO₃ stress concentration, and the higher the concentration, the more obvious the increase. When NaHCO₃ concentration was greater than 0.4%, three types of cold-season turfgrass were damaged. The average value of subordinate function under different concentrations of NaHCO₃ stress followed the order of kentucky bluegrass > ryegrass > tall fescue, indicating that the resistance of kentucky bluegrass to NaHCO₃ stress was stronger than that of ryegrass and tall fescue.

Abstract:Aluminum sulfate improver has a good effect on reducing the pH of soda saline and alkaline soil and promoting soil colloidal condensation and organic carbon accumulation. In order to reveal the effect of aluminum sulfate improver on the carbon sequestration performance of soda saline-alkali soil under straw returning conditions, the adsorption performance of saline-alkaline soil on humic acid was studied after adding straw and aluminum sulfate and culturing for 300 days under constant temperature conditions. The results showed that in the adsorption kinetics of humic acid, under the different addition conditions of straw and aluminum sulfate, the adsorption of humic acid by saline-alkali soil reached the equilibrium of the quasi-second-order kinetic equation at 120 min, R². The highest value (0.936). Both the Langmuir equation and the Freundlich equation can better fit the isothermal adsorption of humic acid by saline-alkaline soil. Under the condition of adding the same proportion of corn stover, the maximum adsorption amount obtained by the Langmuir equation was 69.335, 42.830, 40.498 and 42.593 mg/g, respectively. Under the condition of adding the same proportion of aluminum sulfate improver, the maximum adsorption amounts were 21.358, 32.647, 69.335, 49.232, 62.375 and 42.830 mg/g, respectively.

Abstract:To investigate the desorption characteristics of atrazine in different soils contaminated by atrazine, the desorption behavior and its affecting factors were studied by batch balance method in albic soil, black soil, and saline soil. The results showed that the process of atrazine desorption in the three soils experienced three stages:rapid desorption, slow desorption and finally desorption equilibrium, and the equilibrium time was 12 h. Freundlich equation could better describe the desorption isotherm curve of atrazine in three soils (R²>0.969). ΔG<0,ΔH>0,ΔS>0. This indicated that desorption was a spontaneous and disordered process of heat absorption. Atrazine had the highest desorption rate in saline soil, followed by black soil and albic soil. Increasing the pH value of soil or adding biochar could reduce the desorption capacity of atrazine in soil.

Abstract:To study the removal effects of different eluents on heavy metals contaminated soil with different leaching conditions, a batch experiment was conducted to compare the effects of four eluents (citric acid (CA), tartaric acid (TA), ethylene diaminetetra acetic acid disodium salt (EDTA), and triacetintrisodium salt (NTA)) on removing heavy metals (Pb, Cd, Cu and Zn) from a paddy soil at different concentrations, leaching time, pH values and solid-liquid ratios. Changes in fractions of heavy metals in soil before and after leaching with eluents were analyzed at single factor optimal leaching conditions. The results showed that the optimum leaching concentrations were 0.3 mol/L CA and TA, and were 0.05 mol/L for EDTA and NTA; the optimal leaching time was 480 min for CA and NTA, and was 720 min for EDTA and TA; the optimum leaching pH value was 3 for all 4 eluents; and the optimum solid-liquid ratio was 1:20 for all 4 eluents. At the single factor optimal leaching conditions, EDTA had the best effects removing heavy metals from paddy soil, and the removal rates were 67.4%, 61.0%, 13.8% and 76.0% for Pb, Cd, Zn and Cu, respectively, followed by NTA, and the removal rates were 41.6%, 42.4%, 9.9% and 54.3%, respectively. The removal rates of heavy metals increased with the decreasing eluention pH values, with the increasing solid-liquid ratios, and with the increasing CA and TA concentrations. The desorption kinetics curves of the eluents removing heavy metals from paddy accorded with the pseudo second-order kinetic model. The desorption process was mainly a chemical desorption, and the desorption rates were controlled by heavy metal contents in soil and eluent concentrations. The desorption rates of heavy metals from soil followed the sequence of Cd>Pb≈Zn≈Cu. EDTA and NTA leaching significantly reduced the contents of iron/manganese oxidation and organic binding fractions of Pb, Cd, Zn and Cu, and CA and TA leaching significantly decreased the contents of iron/manganese oxidation fraction of these four heavy metals. The efficiency of the eluents removing heavy metals was EDTA > NTA > CA > TA.

Abstract:In order to explore the remediation method of heavy metal cadmium (Cd) contaminated soil by combining ammonium chloride with citric acid and Celosia argentea L., the effects of ammonium chloride and citric acid on the growth and absorption and enrichment of Cd of C. argentea L., the difference between rhizosphere soil and non-rhizosphere soil, and the effects of ammonium chloride and citric acid on soil Cd content and morphology were studied through field experiment. The results indicated that planting C. argentea L. and applying ammonium chloride treatment (C+AC) could significantly improve the dry weight of above-ground parts of C.argentea L., which increased the yield by 53.03% compared with only planting C. argentea L. (C) treatment. C+CA treatment could improve the ability of Cd absorption and enrichment of C. argentea L., and the Cd content in the above ground parts was 16.64% higher than that of C treatment. The C+AC treatment had the best effect on the accumulation of Cd in the above ground parts of C. argentea L., which was 69.49% higher than that of C treatment. The cultivation of C. argentea L. had significantly reduced the acid-soluble content of Cd in the rhizosphere soil, and the reductions of acid-soluble content of Cd in C, C+AC and C+CA treatments were 10.31%, 15.00% and 12.67%, respectively, which were significantly greater than that in non-rhizosphere soil. The soil Cd reduction rate of C+CA treatment was the highest, which was 5.33%, while that of the CK (without planting C. argentea L.or applying chemicals) was 1.43%, which was only 26.83% of the C+CA treatment. Therefore, the extraction of C.argentea L. still played a key role in Cd reduction, and the best remediation performance of citric acid on surface soil Cd pollution.

Abstract:In order to investigate the effects of IAA on physiological response and cadmium tolerance of Trichosanthes kirilowii Maxim. under cadmium stress, Baoding T. kirilowii (cadmium-tolerant) and Pujiang T. kirilowii were selected as experimental materials, and soil culture experiments were conducted to determine the effects of exogenous IAA (10, 35 and 60 μmol/L) on physiological changes, photosynthetic characteristics, antioxidant enzyme activity and malondialdehyde (MDA) content of these two varieties under 800 μmol/L cadmium stress. The results showed that:(1) Compared with the CK, the average root length, fresh weight of underground part, superoxide dismutase (SOD) activity, chlorophyll content, maximum photochemical efficiency (F_v/F_m) and electron transfer rate (ETR) of the two kinds of T. kirilowii significantly decreased under 800 μmol/L Cd treatment, while the initial fluorescence (F_o), peroxidase (POD) activity, catalase (CAT) activity and MDA content increased significantly, and the lipid peroxidation of cell membrane deepened. (2) With the increasing of IAA concentration, the average root length and fresh weight of underground part of Baoding T. kirilowii increased continuously, with the maximum increase of 24.83% and 40.55%, while those of Pujiang T. kirilowii changed from ascending to descending. (3) After the addition of IAA, the content of chlorophyll a, b, a+b and chlorophyll a/b, F_v/F_m, ETR, SOD, POD and CAT activities in the young leaves of the two varieties increased first and then decreased, while F_o and MDA content dropped firstly and then increased. The content of chlorophyll a, b, a+b, a/b, F_v/F_m, ETR, SOD and CAT increased to the peak values with the addition of IAA at 35 μmol/L, while MDA decreased by 35.44%~43.23%, reaching the valley value. (4) The analysis of membership function indicated that the ability of cadmium tolerance of different IAA concentrations was 35 μmol/L > 10 μmol/L > 60 μmol/L > 0 μmol/L. Therefore, applying exogenous IAA has a certain application prospect in alleviating cadmium stress in plants.

Abstract:Alluvial sandy soil (developed from river alluvium parent materials) and purple clayey soil (developed from purple sandy shale parent materials) with similar available cadmium (Cd) content and different parent materials were selected to conduct pot experiments, and to study the difference of Cd absorption and accumulation at different growth stages of rice under Cd stress conditions in different parent material paddy soils, as well as to calculate the critical value of soil Cd environmental safety. Different concentrations of exogenous Cd (0, 0.5, 1, 2, 5 mg/kg) were added to the soils to simulate the Cd contained paddy soils. The results showed that the available Cd contents of the two soils (alluvial sandy soil and purple clayey soil) were the highest at the tillering stage. The average content of available Cd in alluvial sandy soil was 0.47 mg/kg, and that in purple clayey soil was 0.36 mg/kg. At the same level of exogenous Cd, the content of available Cd in alluvial sandy soil was higher than that in purple clayey soil. For alluvial sandy soil, with the increasing of exogenous Cd concentration, the total biomass of rice increased first and then decreased. When the concentration of exogenous Cd was 1 mg/kg, the biomass was the maximum, which was 47.11 g/pot. While the biomass of rice in purple clayey soil increased gradually, but the difference between the treatments was not significant (P>0.05). The contents of Cd in brown rice, husk, stem and leaf and root increased with the increasing of exogenous Cd concentration in the two soils, and the overall distribution characteristics were root > stem and leaf > husk > brown rice, and the Cd content of alluvial sandy soil was higher than that of purple clayey soil. The average Cd accumulation of rice in alluvial sandy soil was 51.71 g/pot, and it was 42.56 g/pot in the purple clayey soil. Compared with the tillering stage, the Cd accumulation of rice in the two soils increased by 1.45 and 1.07 times at maturation stage, respectively. Regression analysis showed that the critical Cd safety thresholds for Cd-exceeding soil were 2.03 mg/kg and 3.14 mg/kg in alluvial sandy soil and purple clayey soil, respectively. The absorption and accumulation characteristics of Cd and the critical value of soil Cd safety were significantly different among different soil parent materials.

Abstract:To explore the effect of hydroxyapatite (HAP) on the solidification of heavy metals in mining areas, this study conducted the adsorption experiments to study the kinetic adsorption and isothermal adsorption of Cd²⁺ and Zn²⁺ in the soil of Pb-Zn mines with HAP. The results showed that the adsorption of Cd²⁺ and Zn²⁺ increased with the increase of initial concentrations of Cd²⁺ and Zn²⁺; under acidic conditions, the amount of adsorption increased with the increasing pH values; the quasi-second-order kinetic equation could well describe the adsorption process of Zn²⁺ and Cd²⁺, soil adsorption capacities increased with the addition of HAP. In the Zn-Cd coexistence system, when the initial concentration was <20 mg/L, the adsorption of Zn²⁺ and Cd²⁺ in the soil was not significantly different. The competitiveness of the two metal ions was small, and the competition was obvious as the initial concentrations increased. The maximum adsorption capacities of Zn²⁺reached 79%~87% in a single system, while the maximum adsorption capacities of Cd²⁺ was only 57%~72% in a single system. The competitiveness of Zn²⁺ was better than that of Cd²⁺, and Zn²⁺ seriously inhibited the adsorption of Cd²⁺. In summary, HAP could improve the adsorption performance of soil in the mining area, and enhance the adsorption and retention ability of soil to Zn²⁺ in Zn and Cd contaminated soils.

Abstract:To investigate the alleviation of selenium (Se) on the chromium (Cr) toxicity in eggplant, the effects of different concentration of Se on the growth, physiological characteristics and Cr uptake by eggplant under different Cr stress levels were studied by pot experiments. The results showed that with the treatment of single Cr, the plant growth was significantly inhibited with the increase of Cr concentration. The Cr toxicity showed that the plant height, root length, shoot and dry weight and chlorophyll content were inhibited. With the increase of Cr concentrations, the chlorophyll and soluble protein in leaves showed a downward trend, and the content of malondialdehyde (MDA) increased, the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) increased first and then decreased. The results of Cr-Se mixed treatment showed that Se could alleviate the Cr toxicity of eggplant. Under different concentrations of Cr stress, Se applied with different concentrations showed different alleviation effects. Studies showed that under the treatment of 10, 20, 40 and 80 mg/kg Cr, the good alleviation effects could be obtained when applied with 12, 24, 48 and 48 mg/kg Se respectively. The plant height, root length and biomass of eggplant increased, chlorophyll and soluble protein contents increased significantly, MDA and Cr accumulation in plant decreased.

Abstract:Biological simulation of the hydroponic experiment was conducted to explore the effects of spraying eight different foliar silicon solutions on total arsenic (As) accumulation and As speciation in rice seedling. The results showed that the application of foliar silicon conditioner reduced As content in rice roots and shoots. Moreover, As contents in roots and shoots of rice seedlings treated with Na₂SiO₃+rhamnolipid (Si6) were the lowest, 10.04 mg/kg and 0.31 mg/kg, respectively, which were 25.35% and 33.10% lower than those of the control (P<0.05), respectively. As (Ⅲ) was the predominant speciation of As in rice. Compared to the control, foliar application of solution with Na₂SiO₃+rhamnolipid significantly reduced the As (Ⅲ) contents in roots and shoots by 27.74% and 21.50%(P<0.05), respectively. Considering the accumulation of As in rice roots and shoots and the transport of As from roots to shoots, the cluster analysis of different silicon conditioner treatments showed that the treatment of spraying Na₂SiO₃+rhamnolipid was a low accumulation group of As in rice. Therefore, the rhamnolipid as bio-surfactant combined with silicate solution was the best silicon conditioner for inhibiting the uptake and accumulation of As in rice seedlings, which would provide technical support for food security of rice in As-contaminated regions of China.

Abstract:A hydroponic experiment was carried out to explore the effects of Si/As ratios (0:1,100:1 and 200:1) on the uptake, efflux, translocation and accumulation of arsenic in rice seedlings that were grown in nutrient solution containing 10 μmol/L arsenite or arsenate for 12, 24,48 h. The results showed that Si/As of 200:1 reduced arsenite uptake rate compared to Si/As of 0:1, accounting for 30.7% (P<0.05), when rice was exposed to nutrient solution with arsenite and silicon for 12 h. The uptake rates of arsenite of rice gradually decreased and the effect of different Si/As ratios reduced with the prolongation of exposure time. Furthermore, compared to Si/As of 0:1, the ratios of Si/As at 100:1 and 200:1 inhibited the translocation of arsenite from roots to shoot and the concentrations of As(Ⅲ) were decreased by 51.2% and 56.9%, respectively, when rice seedlings exposed to nutrient solution with arsenite for 48 h, at the same time, the concentrations of As(Ⅲ) in rice shoots were significantly lower than Si/As of 0:1, accounting for 50.7% and 67.2%, respectively. When rice seedlings were exposed to arsenate nutrient solution for 12 h, Si/As of 100:1 promoted the uptake rate of arsenate by rice, which was 82.3% higher than Si/As of 0:1. However, the ratio of Si/As of 200:1 inhibited the uptake rates of arsenate, arsenite efflux by rice roots and translocation of As(Ⅲ) after 24 h for exposure to asenate, accounting for 28.0%, 41.9% and 39.9%, respectively. The translocation of As(Ⅲ) from root to shoot with Si/As of 200:1 was 57.9% lower than that of Si/As of 100:1 after 48 h of exposure time. In addition, the concentrations of As(Ⅲ) in rice shoots in the treatment of Si/As ratio at 100:1 and 200:1 for 24 h or 48 h were significantly lower than the control, accounting for 53.6% and 75.0%, 25.0% and 52.8%. In addition, there was a significant positive correlation between the uptake of As(V) and the efflux of As(Ⅲ) in rice roots (r=0.921, P<0.01), which was not affected by Si/As and exposure time. In summary, when rice seedlings were exposed in nutrient solution with As(Ⅲ) or As(V) for 12~48 h, the ratio of Si/As at 200:1 significantly inhibited arsenic uptake, As(Ⅲ) efflux and translocation of As(Ⅲ) from root to shoot in rice.