Abstract:The black soil region of Northeast China is an important commodity grain production base of our country. Intensive soil and water loss declines both the thickness and quality of the black soil, thereby threatening the national food security directly. It is therefore of great importance to systematically examine soil erosion research outcomes in the black soil region, which hold essential implications for the prevention and alleviation of black soil degradation, the maintenance of land productivity, and the assurance of national food security. In the current study, the researches on soil erosion environment and its effects, soil erosion processes and mechanisms, spatio-temporal variability of soil erosion in the black soil region were analyzed and concluded, and future research perspectives on soil erosion were proposed. The erosion environment of the black soil region is characterized by various erosive agents and their different combinations, as well as long gentle slopes. The direct impacts of such erosion environment are declining black soil thickness and soil quality degradation of slope farmlands. The erosion mechanisms and dominant influencing factors vary with erosion type, which include interrill, rill, ephemeral gully, gully and freeze-thaw erosion. The feedback of sediment transport induced by energy consumption to soil detachment is the dominant reason for the alternative pattern of strong and weak soil erosion intensity with slope length. Ephemeral gully and gully mainly emerge on slope farmlands, and soil erosion intensity is significantly affected by anthropogenic activities. Although notably weaker than water erosion, the freeze-thaw erosion in this region can influence water erosion via reducing soil erosion resistance and enhancing both surface and subsurface runoff. At the catchment scale, the type and intensity of soil erosion apparently change vertically along the slope, i.e., from slope summit towards toe, whereas at the regional scale, they exhibit clear latitudinal and longitudinal zonality along the north-east and west-east directions, respectively. Global climate change may enhance water erosion but reduce freeze-thaw erosion in the black soil region. Future research should focus on the response mechanisms of black soil thickness and land productivity to soil erosion, the dynamic processes and coupling mechanisms of complex soil erosion, as well as the spatio-temporal variability and controlling factors of typical soil erosion types.

Abstract:Hydrological resilience is an important reference index for maintaining hydrologic stability of watershed or ecosystem. An in-depth study of the relationship between vegetation structure and hydrological resilience will be an important direction of ecological hydrology under the background of global change in the future. However, there is still a lack of systematic research on the response mechanism of hydrological resilience to different intervention modes such as climate change and human activities, then the formation mechanism of hydrological resilience and its relationship with vegetation structure have not been fully understood. This paper systematically summarized the main concepts of hydrological resilience, and five main algorithms from different perspectives such as water use efficiency, water balance of Budyko framework, vegetation landscape structure change and recovery time disturbed by drought. The responses of climate change, human activities and vegetation structure to hydrological resilience were analyzed, and the internal mechanism of hydrological resilience was analyzed. (1) Budyko model and water use efficiency of ecosystem have significant value in the calculation of hydrological resilience. (2) In the energy-limited watershed, the hydrological resilience decreases with the increases of the degrees of warming and drying. In the water-limited watersheds, the hydrological resilience increases with the increases of the degrees of warming and drying. (3) Forest-dominated watersheds have higher hydrological resilience than other bioceno-dominated catchments. (4) Large-scale deforestation or afforestation usually reduces the hydrological resilience of watersheds. (5) Natural forest and vegetation structure with high diversity are conducive to maintaining high hydrological resilience. (6) The watersheds with higher water use efficiency of vegetation under disturbance are conducive to maintaining high hydrological resilience. (7)The hydrological resilience of the watershed with high diversity of vegetation, low degree of landscape fragmentation, stable vegetation structure, large soil water storage or snow replenishment was higher. It is necessary to explore and develop hydrological resilience calculation methods under various stable states in the future.

Abstract:In order to understand the impacts of different grass strip widths on the soil and water loss of in purple soil sloping farmland, taking the Agrostis stolonifera grass strips paved on purple soil slope as the research objects, and through the indoor simulated scouring, we study the impacts of different grass strip widths and drainage scouring flows on the slope rill erosion morphology and the effects of sediment and flow reduction. The bare slope was used as the control group. The results showed that:(1) With the increasing of grass strip width, the rill depth decreased first and then increased, while the rill width, rill length and width-depth ratio showed a contrary tendency. In addition, the rill width, rill length and rill depth increased with the increasing of discharge, but the change of width-depth ratio was not obvious. (2) When the discharge flow was small (4 L/min), the runoff and sediment yield rate decreased with the increasing of grass strip width, and the outflow runoff decreased by 48.41% by for the 100 cm grass strip, which was the greatest. When the discharge was large (8 L/min), the 75 cm grass strip had the minimum runoff and sediment yield rate, which had the maximum reduction rate of runoff (20.07%) and sediment (58.11%). (3) Under interception of the grass strip, the runoff and sediment yield rate and soil erosion rate had significant correlation with rill width and rill depth. Compared with runoff interception and reduction, the grass strip had more significant impact on sediment interception and reduction. From these results we concluded that the grass strip was very efficient in reducing the runoff and sediment, and had a good control effect on water and soil loss of purple soil sloping farmland.

Abstract:Slope topographic relief is an important factor affecting soil erosion. The relationship between surface roughness, sediment yield and hydrodynamic parameters is the basis for studying slope soil erosion process. The relationship between surface roughness and erosion characteristic parameters in slope erosion process in exposed Pisha sandstone area is studied by field in-situ simulated scour test and terrain factor parameters extracted by ArcGIS. The results showed that:(1) With the increase of scour intensity, the characteristic parameters of resistance decrease gradually, and the characteristic parameters of sediment yield and flow and other hydraulic parameters increase as a whole. With the increase of scouring time, Froude number showed a decreasing trend and other hydraulic parameters showed an increasing trend. The values of Reynolds numbers were all less than 500 under the three scour flow conditions, and the runoff was in laminar flow state. However, when the scour intensity increased, the Froude number showed the law of flow state from slow flow to rapid flow. (2) The change law of surface roughness was not obvious with the increase of scour flow. When the scour intensity was small (<100 L/h), the relationship between surface roughness and sediment yield characteristics was close. (3) Velocity had a significant power function relationship with surface roughness (R²>0.561), which is the optimal parameter reflecting the change of surface roughness. (4) Through Mantel correlation analysis, it was found that with the increase of scour intensity, the change of surface roughness will change from sediment yield characteristics to hydrodynamic parameters characteristics. The results are aimed to reveal the relationship between surface roughness and characteristic parameters of soil erosion process, and provide theoretical basis for the construction of slope soil erosion model in the exposed Pisha sandstone area.

Abstract:The purpose of this study was to investigate the soil erosion process on the riverbank and establish the prediction models. Under the conditions of four slope gradients and two rainfall intensities, artificial simulated splash erosion test and micro area simulated rainfall test were carried out on typical riverbank in coastal plain sandy soil area of Jiangsu Province, so as to understand the characteristics of soil splash erosion, clarify the production process of runoff and sediment. The estimation models of splash erosion rate, runoff intensity and sediment yield intensity were established using the transfer function method. The results showed that:(1) The soil splash erosion rate on the riverbank increased with the increasing of rainfall intensity and slope gradient. There was a linear relationship between soil splash erosion rate and rainfall intensity and slope gradient. (2) The runoff production process on the riverbank generally showed a trend of increasing first and then fluctuating and stabile, and the runoff production intensity decreased with the increasing of slope gradient. In general, the sediment yield process increased rapidly first and then decreased with fluctuation, and finally tended to be stable. The sediment yield intensity increased with the increasing of slope gradient. The intensity of runoff and sediment both increased with the increasing of rainfall intensity. (3) The equation established by transfer function had high accuracy in predicting splash erosion rate, runoff intensity and sediment yield intensity, and the adjustment R² of the equation could reach 0.97, 0.91 and 0.72, respectively. The results could deepen the understanding of the law of soil erosion on riverbank in plain area of Jiangsu Province, and provide a theoretical basis for establishing soil erosion prediction model and soil erosion control.

Abstract:Based on the investigation and statistics of karst slope near-surface karst conduits, this paper established a test micro-area of surface-underground binary space water and soil process in Karst area. Through artificial simulated rainfall test, the influence of pore size (1 cm, 2 cm, 5 cm) of karst conduits on water and soil leakage process under different rainfall intensities (52 mm/h and 133 mm/h) was studied. The results showed that:(1) The coefficient of underground runoff and the intensity of runoff increased significantly with the increases of pore size of karst conduits, but the effect on the initial runoff time was not significant. Under the moderate rain intensity (52 mm/h), the time required for initial runoff generation increased with the increases of pore size. However, under heavy rain (133 mm/h), the initial runoff time decreased with the increases of pore size. (2) With the increases of pore size, the characteristic curve of runoff intensity under moderate rain intensity (52 mm/h) showed that it increased first and then tended to be stable. The runoff intensity at mid-slope position was proportional to the pore size, and the upstream and downhill positions were not significantly affected by the pore size. The change order of runoff intensity with the pore size was 5 cm>1 cm>2 cm. The runoff intensity under heavy rain (133 mm/h) showed a continuous upward trend with the increases of pore size, and the gross runoff intensity at 2 cm and 5 cm aperture increased by 75% and 74% respectively compared with that at 1 cm. (3) Underground sediment yield of different karst conduits was proportional to their pore size. Under medium rain intensity (52 mm/h), the sediment yield of 2 cm and 5 cm karst conduits with pore diameter was 2.5 and 14.9 times of that of 1 cm respectively. Under heavy rain (133 mm/h), the sediment yield of 2 cm and 5 cm karst conduit with pore diameter was 6.9 and 10.3 times of that of 1 cm respectively. (4) Under heavy rain (133 mm/h), the order of mass loss of sediment in different particle size ranges was:particle size less than 2 mm>3~2 mm>5~3 mm>5 mm or more. These research results are helpful to further understand the influence of karst pore size on underground leakage in southwest karst area and provide reference for water and soil erosion prevention in this area.

Abstract:Remarkable achievement has been obtained since the implementation of the Grain for Green project in China. Aiming to explore the improvement effect of restoration years on soil properties and infiltration performance and its mechanism, the water stable aggregate characteristics, root characteristics and infiltration rate of 30-cm-depth farmland and grassland soils with 5-year (C_{5 a}), 15-year (C_{15 a}) and 25-year (C_{25 a}) restoration in the Loess Hilly and gully area were measured. The factors affecting soil infiltration were analyzed. The results showed that the organic matter content (SOM), total nitrogen content and root traits of grassland soil with different abandoned years were C_{25 a}>C_{15 a}>farmland≈C_{5 a}. The mean weight diameter (MWD), geometric mean diameter (GMD), fractal dimension (D) of 0-30 cm soil aggregates and initial infiltration rate (IIR) and stable infiltration rate (SIR) were 0.78, 0.2 mm, 2.89, 7.80 and 2.58 mm/min for farmland; 2.03, 0.62 mm, 2.73, 6.36 and 3.21 mm/min for 5-year grassland; 2.25, 0.77 mm, 2.69, 11.12 and 4.33 mm/min for 15-year grassland; 2.44, 0.93 mm, 2.64, 13.67 and 5.93 mm/min for 25-year grassland, respectively. There was a significant positive correlation between soil SIR and SOM, bulk density and aggregate content of >5 mm (P<0.01). The improvement effect to soil of restoration continues to increase with the extending years of Grain for Green. Therefore, the existing achievements of Grain for Green should be maintained in areas with serious soil and water loss, and the manual intervention and management in the early (5-year) stage of restoration should be strengthened to realize its potential ecological value in the later stages.

Abstract:In order to explore the water infiltration characteristics and optimal infiltration model of arsenic sandstone soil (gray white, mixed color, purplish red) with different textures under different slopes (5°, 10°, 20°, 30°), the characteristics of soil water infiltration and fitting results were compared and analyzed by indoor simulated soil column method. The results showed that:(1) The soil bulk density of different slopes in the study area is 1.513~1.737 g/cm³. The soil infiltration capacity of gray white arsenic sandstone under 30° slope was strong, and the soil infiltration capacity of purple red arsenic sandstone under 5° slope was weak. (2) In the process of one-dimensional vertical infiltration of arsenic sandstone soil, the initial infiltration rate was 2.000~8.600 cm/min, and the stable infiltration rate (0.160~1.800 cm/min) was reached after the infiltration time was 3.500~5.000 min. The infiltration rate and wetting front migration rate decreased with time in a power function. The smaller the slope and the darker the color was, the lower the infiltration rate and cumulative infiltration rate was, and the slower the migration of wetting front was. The values of initial infiltration rate, stable infiltration rate, initial wetting front migration rate, and stable wetting front rate all decreased with the decrease of slope gradient and the deepening of arsenic sandstone soil color. (3) Kostiakov model and Philip model fit well the results of soil water infiltration in arsenic sandstone area, and the determination coefficients were more than 0.900. The average value of the decision coefficient of Kostiakov model was 0.948, and the fitting effect was the best. The average value of Philip model determination coefficient was 0.937, and the fitting effect was the second. The average value of the determination coefficient of Horton model was 0.688, and the fitting effect was poor. Through the mean absolute error (MAE), root mean square error (RMSE), percentage of deviation (PBIAS), and Nash efficiency coefficient (NSE), it was verified that the simulated values of Kostiakov model and Philip model have little difference and high degree of coincidence with the measured values.

Abstract:In order to quantitatively evaluate the impact of grazing on the process of grassland soil infiltration, understand and prevent soil erosion by grazing and scientifically evaluate the hydrological regulation function of grassland, this study took Xilamuren grassland as the main research object and used the double-loop infiltration method to study the effects of grazing on soil infiltration performance of typical grassland and collected the environmental characteristic variables affecting soil infiltration. The results showed that:(1) The soil infiltration capacity was disturbed by grazing activities. With the increasing of grazing intensity, the initial soil infiltration rate and steady infiltration rate decreased, and the time to reach steady infiltration shortened. However, light grazing (LG) enhanced the infiltration performance of the soil. The initial infiltration rate (5.12 mm/min), steady infiltration rate (1.93 mm/min) and cumulative infiltration capacity (213.42 mm) for 2 hours were all good under the LG condition. The duration from the rapid infiltration stage to the stable infiltration stage of LG was prolonged. (2) Under different grazing intensities, there was a significant negative correlation between grazing intensity and soil initial infiltration rate, steady infiltration rate and cumulative infiltration amount, and the correlation coefficients were -0.646, -0.770 and -0.531, respectively. Vegetation coverage, sand volume percentage and porosity were all positively related to soil infiltration rate, while soil bulk density was the opposite. Soil bulk density, total porosity and capillary porosity had the most significant effect on soil infiltration rate. Appropriate grazing (LG, 1.5 sheep/(hm²·month)) improved soil characteristic parameters and vegetation growth, and increased soil infiltration performance. (3) Through the analysis of soil infiltration model, the Horton model had the best fitting effect on soil infiltration rate and soil cumulative infiltration. This study could provide a reference for the quantitative evaluation of soil infiltration and hydrological regulation function of typical grassland under grazing conditions.

Abstract:To reveal the effects of crushed corn straw returning on soil erosion characteristics at the black soil hillslopes, the simulated rainfall experiments were carried out based on different amounts of crushed corn straw returning (0, 25%, 50%, 75% and 100%) under different slope gradients (3°, 5° and 7°). The results showed that the crushed corn straw returning could regulate runoff, and delay the runoff-yield time; and thus, the runoff rates and runoff values decreased. Moreover, with the increasing amounts of the crushed corn straw returning, the runoff-yield time delayed more and the mean runoff velocity obviously decreased. For the 3° hillslope, the 25% and 100% of crushed corn straw returning treatments showed better runoff regulation effects; while for the 5° and 7° hillslopes, the 50% and 75% treatments showed the better. Furthermore, the crushed corn straw returning could decrease the sediment rates and soil erosion to a certain extent. When the amount of the crushed corn straw returning was lower (<50%), the sediment rates and soil erosion were also lower under gentle slope gradients (3° and 5°), which illustrated that the treatments showed relatively better soil erosion regulation effects. Among them, the soil erosion regulation effect for the 25% of crushed corn straw returning treatment could reach 74.1% under the 3° slope gradient. When the amount of the crushed corn straw returning was greater (>50%), the soil erosion regulation effects increased with the increases in the slope gradients. Among them, the soil erosion regulation effect for the 100% of crushed corn straw returning treatment could reach 72.1% under the 7° slope gradient. Therefore, it is necessary to select appropriate corn straw returning patterns and amounts based on concrete slope gradients and other topographic characteristics in the practice of agricultural production.

Abstract:Based on the satellite remote sensing data from 2000 to 2020 and the daily sandstorm data of seven meteorological stations from 1961 to 2020 in the Shiyang River Basin, we analyzed the multi-scale variation characteristics and relationship between watershed vegetation coverage and sandstorm frequency, duration and intensity, and explored its influence on the occurrence and development of sandstorm by using the methods of univariate regression trend method, linear tendency rate and correlation coefficient. The results showed that the watershed vegetation coverage increased slightly, and NDVI increased at the rate of 0.000 9 per year. The NDVI began to recover in 2007. Recovery was more obvious after 2010, and the recovery rates in the upper and middle reaches were faster than that in the lower reaches. The sandstorm frequency decreased significantly, and the interannual trend rate was -2.8 d/10 a. It decreased the most significantly in the past 10 years, which was 14.5 days less than that in the 1970s. The rate of reduction was slower in the middle reaches and that was faster in the lower reaches. The rate of reduction in four seasons followed the order of spring>summer>winter>autumn. The sandstorm duration was significantly shortened, the interannual trend rate was -12.2 m/10 a. The duration in the last 10 years was the shortest, which was 60.9 min shorter than that in the 1970s. The shorting time in the middle reaches was slower and that was faster in the lower reaches. The sandstorm intensity had no obvious change, and the minimum visibility was around 0.496 km. The frequency and duration of sandstorm were negatively correlated with full-basin NDVI, NDVI >0.3 area, NDVI of upper, middle and lower reaches in the current year and the previous year. The sandstorm intensity had a weak negative correlation with full-basin NDVI, NDVI >0.3 area, NDVI of upper, middle and lower reaches, and a weak positive correlation with NDVI of the previous year. The improvement of vegetation cover in the watershed had obvious restraining effect on sandstorm.

Abstract:The influences of moss cover on detachment process of carbonate derived laterite in karst mountainous lands were explored and analysed. Undisturbed soil samples were collected and subjected to flow scouring in a 3.5 m long hydraulic flume. Two degrees of slope (5°, 20°) and two soil water contents (saturated soil water content, field capacity) were selected to quantify the relationship between moss coverage and soil detachment rate. The responses of hydraulic characteristics of slope runoff to moss cover were also analyzed. Compared to the field capacity, the results indicated that the detachment rate of saturated soil under moss cover increased by 33.9% and 10.8% at slopes of 5 and 20 degrees, respectively. The effects of moss cover on reducing soil detachment rate were more effective than that of bare soil without moss cover, and its effects were more obvious at lower slopes. The detachment rate under field capacity soil condition decreased in a linear trend with increasing moss coverage (R²>0.995). The moss cover had significant effects on the hydraulic characteristics of runoff flow at the slope of 5 degrees. The moss cover under saturated soil condition significantly changed the flow regime of surface runoff (P<0.05). Compared to bare soil without moss cover, the moss cover significantly reduced the runoff velocity (-20.6%), Reynolds number (-0.6%), Froude number (-28.6%) and runoff power (-0.8%), increased the runoff depth (+27.8%), flow shear stress (+26.9%) and Darcy-Weisbach resistance coefficient (+117.0%). Besides, the moss cover had no significant effects on the hydraulic characteristics of slope runoff at the slope of 20 degrees. Overall, no significant correlation exhibited between the hydraulic characteristics of runoff flow and the soil detachment rate of carbonate derived laterite covered with moss. These results can provide the experimental data for the study of applying moss cover to soil and water conservation in karst mountainous lands.

Abstract:To quantify the influence of root water absorption on unsaturated soils slope stability and provide reference for plant species selection of vegetation slope protection, a two-dimensional slope was established by COMSOL Multiphysics. The distribution of pore-water pressure in unsaturated soils slope caused by root water absorption under different root morphology, root length and rainfall conditions was simulated, and the slope stability factor was quantitatively calculated using the limit equilibrium method. Results demonstrated that the suction generated by the exponential root uptake water is the largest, which is 4.2 times larger than that of the bare slope, and the suction generated by the parabolic root uptake water is the smallest, which is still 2.7 times larger than that of the bare slope. The longer the root was, the greater the influential depth of water uptake was. The shorter the root was, the greater the suction generated, and the more remarkable the change of suction on the slope surface. After short-term rainfall, the suction of root soil slope was still 12~20 kPa higher than that of bare slope. The exponential root system contributed more to the stability improvement of unsaturated soils slope, which was 1.54 times higher than that of bare slope. While the parabolic root system was the smallest, but it was still 1.36 times higher than that of bare slope. The root water absorption has a positive effect on the stability of the unsaturated soils slope. For vegetation slope protection, priority will be give to the vegetation with the exponential root.

Abstract:The implementation of the "grain-for-green" project has effectively mitigated soil erosion of hill slope on the Loess Plateau. However, gravity erosion, including both shallow landslide and collapse, is widely distributed on the Loess Plateau and has become one of the dominant source of erosion sediment in small watershed. To explore the morphological characteristics and critical topography of shallow landslide and collapse in hilly and gully region of the Loess Plateau, 53 shallow landslides and 40 collapses were investigated in Zhifanggou small watershed in Ansai District, Shaanxi Province, and their vegetation characteristics were also recorded. Photogrammetry was performed by unmanaged aircraft vehicle. The results showed that the sizes of shallow landslide were usually larger than those of collapse. The variations in morphological characteristics of shallow landslide were greater than those of collapse. The length, width, perimeter and area of shallow landslide were negatively correlated with gully density (P<0.01), and were positively correlated with the distance to gully system (P<0.01). Nevertheless, the correlations between the morphological characteristics of collapse, and gully density and distance were loose. Shallow landslide and collapse were concentrated on where the slope and topographic wetness index (30°~55° and 0.50~2.00) were moderate, flow path gradient and flow path length were small (60.0%~120.0% and 0~15.00 m). Nevertheless, in areas where the slope and flow path gradient were large (>55° and >120.0%), and the topographic wetness index and flow path length were small (<0.50 and <15.00 m), gravity erosion was dominated by collapse. On the contrary, in areas where the slope and flow path gradient were small (<30° and <120.0%), and the topographic wetness index and flow path length were large (>2.00 and >15.00 m), gravity erosion was dominated by shallow landslide. Shallow landslide and collapse widely occurred on slopes covered by shrub communities with the aspect of 0~180°. Shallow landslide was also distributed on slopes covered by herbs with the aspects of 0~90° and 270°~360°. The research results are helpful for understanding the occurrence process and critical topographic conditions of shallow landslide and collapse estimating sediment yield and controlling erosion in small watershed.

Abstract:In order to improve the stability of Benggang soil, prevent Benggang wall collapse, an experiment was conducted to study the crack evolution rules and shrinkage deformation rules of Benggang soil under the effect of Dry-Wet (D-W) cycles. A total of six D-W cycles were designed for the experiment, in which the four layers of soil were photographed at a fixed time and fixed site by using industrial cameras during the dehumidification process and in combination of digital image processing technology. Results showed as follows:(1) In the process of dehumidification, the sequence of soil morphology changes was:axial shrinkage, radial shrinkage, and crack development. (2) There was an obvious positive correlation between shrinkage cracking degree and liquid limit, plastic index and clay content. The maximum value of shrinkage cracking degree in the four layers of soil was 18.78% for the transition layer, and the minimum value was 5.41% for the sandy layer. The two soil layers were adjacent to each other on the section of the Benggang, and their great difference caused the terrible influence on the stability of Benggang. (3) As the D-W cycles, the radial shrinkage phenomenon no longer occurred. The rate of axial shrinkage, the rate of surface cracks, and the average width of the cracks gradually decreased. The total length of the cracks, the total number of crack strips, the number of crack intersections, and the number of lumps initially increased, then decreased, all parameters stabilized after the 3rd D-W cycles. Among the four soil layers, the transition layer was the most affected by D-W cycles, and the sandy layer was the smallest. These results could provide a scientific basis for the study on the mechanism of Benggang occurrence during the rain-evaporation cycles.

Abstract:The changes of river runoff and sediment directly reflect the ecological environment and the degree of soil erosion in the basin. In order to explore the variation characteristics of runoff and sediment and its' driving mechanism in the typical soil erosion control area in South China, the runoff and sediment data of Changting section of Tingjiang River Basin from January 1982 to December 2014 were taking as the research object, and the CEEMDAN, Mann-Kendall trend test, Pettitt test and water sediment relationship model were used to analyze the variation characteristics of runoff and sediment. Meanwhile, the double accumulation curve was used to quantitatively study the contribution of rainfall and human activities to the changes of runoff and sediment. The results showed that:(1) The rainfall and runoff in Changting section of Tingjiang River Basin showed no significant decreasing trend, while the sediment rate decreased significantly (p<0.01). The periodicity and trend of runoff and sediment were not synchronous. (2) The sediment transport rate in Changting section of Tingjiang River basin changed suddenly in 2000 (p<0.01). After 2000, the runoff sediment concentration decreased and the inflow sediment coefficient of water sediment relationship curve decreased significantly. (3) The total amounts of runoff and sediment in Changting section decreased after 2000. The contribution rate of human activities to the change of runoff was 68%~81%, and the contribution rate of human activities to the change of sediment was 90%~98%. In human activities, the implementation of soil and water conservation measures dominated by banning management and ecological forest and grass construction were the most important reasons for the reduction of sediment.

Abstract:Soil hydrothermal factor is an important factor affecting the growth and development of crops, especially during the natural vegetation restoration on the Loess Plateau. The dynamic changes and correlations of soil temperature and water in the process of vegetation restoration were studied through long-term monitoring of soil water and temperature in different stages of natural vegetation restoration in the Loess Plateau. The results showed that soil temperature in the grassland community from August to October is significantly higher than other communities, and it is significantly higher in Quercus liaotungens community in November, with the vegetation restoration, the range and the peak of soil temperature decreased with different degree, soil water content decreased but it does not affect the overall varying trend over time, soil temperature and soil water content have significantly negative correlation in the different stages of vegetation restoration, and the soil water content has a certain time stability during the restoration process. The research results provide scientific reference for the effective management and sustainable development of natural vegetation restoration on the Loess Plateau.

Abstract:River bank slope is the main source of soil and water loss in plain area. Land use is an important external factor affecting soil and water loss of slope. The study on land use of river bank slope can provide basic data for soil and water loss control in the region. Based on unmanned aerial vehicle (UAV) aerial images and field survey data, this study counted the areas under four land use types of rivers bank slope in Jiangsu Province, and analyzed the slope use characteristics of sandy soil area, non-sandy soil area and different soil and water conservation regionalizations. The results showed as follows:(1) The land uses of river slope in the study area mainly include grassland, woodland, cultivated land, bare land, slope protection land and others, and the corresponding proportions of each type were 38.15%, 34.45%, 19.66%, 6.10%, 0.93% and 0.70%, respectively. Farmland and bare land accounted for 25.76% of the total. It indicated that the river bank slope was strongly interfered by human beings, and there was a serious risk of soil erosion. (2) The proportions of woodland, farmland and bare land in sandy soil area were 11.77%, 5.62% and 4.43% higher than those in non-sandy soil area, respectively. The proportions of grassland and slope protection land were 21.00% and 0.63% lower than those in non-sandy soil area, respectively, indicating that the potential risk of soil and water loss in sandy soil area was greater. (3) In the same river length range, the area of river slope in the northern rocky mountain area was larger than that in the southern red soil area. The proportions of grassland and bare land in the rocky mountain area were 16.64% and 8.00% larger than those of the red soil area. The proportions of woodland, farmland and slope protection land in the rocky mountain area were 15.17% and 10.08% lower than those of the red soil area. The appropriate measures should be adopted for soil erosion control according to the environmental characteristics of each region. This research can provide a theoretical basis for the design of regional river slope treatment.

Abstract:In order to reveal the characteristics of confluence network of different micro-topography types, field artificial rainfall simulation experiments were conducted. The confluence networks of seven micro-topography types were abstracted and analyzed by close-range photogrammetry. The rainfall events with 60, 90 and 120 mm/h rainfall intensity lasted for 90 minutes. The seven micro-topography types were continuous depressions, alternate depressions, continuous mounds, alternate mounds, continuous mounds and depressions, alternate mounds and depressions, and smooth slope. The results showed that:(1) The drainage density gradually decreased with the increasing of drainage area threshold. The optimal thresholds for alternate depressions and continuous mounds and depressions were 450 m², those for smooth slope, continuous depressions and alternate mounds were 550 m², and those for continuous mounds and alternate mounds and depressions were 650 m². (2) The morphology of confluence network of the control group, continuous depressions and alternate depressions was dendritic pattern. The confluence network of alternate mounds and alternate mounds and depressions was mixed pattern, which was a mixture of dendritic pattern and parallel pattern. The confluence network of continuous mounds and continuous mounds and depressions was parallel pattern. In the micro-topography, depression played a role in collecting runoff and reducing the amount of low-level runoff, while the mound played a role in changing runoff direction and reducing convergence possibility of runoff. (3) The drainage density and stream frequency of the seven micro-topography types followed the order of dendritic pattern>mixed pattern>parallel pattern. With the rainfall intensity increased, the stream frequency generally increased while the drainage density changed only a little.

Abstract:Precipitation is an important source of water in desert steppe ecosystem, and is also an important driving factor of various biological processes on different spatial and temporal scales. In order to understand the response of desert steppe soil moisture to precipitation, this study took three typical land use patterns (natural grassland, shrub land and sandy land) in desert steppe as research objects to study the effect of precipitation events on soil moisture under different land use types. The results showed that precipitation in the study period was mainly small precipitation events less than 5 mm, accounting for 72% of the total. Judging from the precipitation rate, precipitation events less than 10 mm/h were the majority, reaching 86%. The average soil water content of 0~250 cm was highest in sandy land. The average soil water contents of shrub forest and natural grassland were almost equal, but the average soil water content of natural grassland fluctuated greatly. Under the three types of land use, the soil water content fluctuated greatly in the surface layer (<10 cm), while it was relatively stable in the deep (>80 cm). Compared with grassland and shrub land, the wet front of sand had the fastest response and the largest infiltration depth. Under the rainfall of 102.6 mm, the cumulative infiltration amount of natural grassland was the largest (7.36 mm), followed by sand (3.47 mm), and shrub land (2.64 mm). Therefore, from the point of view of maximum storage and effective utilization of precipitation resources, natural grassland should be a land use type worthy of selection during the ecological restoration and reconstruction of desert steppe.

Abstract:In order to explore the effects of different microtopographic characteristics on splash erosion, so as to provide scientific basis for soil and water conservation tillage in the Loess Plateau, the Yangling Lou soil was taken as the research object. Through indoor artificial simulation rainfall experiment (rainfall intensity was 20 mm/h, 40 mm/h, 60 mm/h, 80 mm/h, 100 mm/h, 120 mm/h, respectively, lasting for 10 min), the influence of microtopographic units caused by different tillage measures (land leveling, dibble sowing, drill sowing) on splash erosion were studied. The results showed that:(1) Under different slope conditions (0, 6°, 10°, 13°, 20°, 26°), the total amount of splash erosion in cultivated microtopographic unit increased linearly with the increases of rainfall intensities (R² ≥ 0.95). (2) The amount of splash erosion on the downward slope in the microtopographic unit was a bivariate linear function with the changes of slope and rainfall intensities (R² ≥ 0.90). (3) The micro slope direction in the cultivated micro terrain unit would affect the direction and distribution of splash erosion. The research results could provide a reference for revealing the causes of splash corrosion and perfecting the splash corrosion mechanism.

Abstract:The nitrogen (N) use status and soil fertility and wheat yield were studied under the condition of reduced urea N input and combined with organic matter, to provide a theoretical basis for winter wheat cultivation in the North China Plain, in terms of improving the N use and fertilizer efficiencies. Field trials were carried out with five treatments:no N application (CK), farmer N application (FN), 20% reduction N application (80% FN), 20% reduction N application with bio-organic manure (80% FN+OM), and 20% reduction N application with biochar (80% FN+BC). In the study, the responses of soil bulk density, organic matter, NO₃^--N, microbial diversity, yield, and N utilization of wheat were measured under winter wheat-maize rotation systematically. The results showed that soil capacity was significantly influenced by the application of organic matter. Compared with 80% FN, the soil bulk density in 80% FN+OM and 80% FN+BC were decreased by 3.83%~4.58% and 2.96%~5.07% in 0-20 and 20-40 cm at maturity stage, respectively. Soil organic matter content of 80% FN+OM was higher than other treatments, and greater by 2.13%~18.81% with 80% FN+OM than N fertilizer treatments in 0-40 cm at maturity stage. Soil NO₃^--N was significantly affected by the application of N fertilizer. Soil NO₃^--N was higher in 80% FN+OM and 80% FN+BC than other treatments in 0-40 cm at flag raising stage. Soil NO₃^--N content with 80% FN+BC was higher than other treatments in 0-80 cm at grouting stage. The soil NO₃^--N residues of FN treatment was higher than other treatments at maturity. Combined application of organic matter could improve soil microbial diversity, increase the number of bacteria OTU, balance the relative abundance of bacteria, and stabilize the soil micro ecological environment. The wheat yield and N agronomic efficiency with 80% FN+OM were 1.09%~7.34% and 2.78%~41.49% higher than other N application treatments, respectively. In the perspective of soil physical and chemical properties, N reduction combined with bio-organic manure rather than with biochar could promote soil quality through increasing soil physical and chemical properties, soil microbial diversity, and wheat production. It is recommended that scientific application of N fertilizer combined with organic matter could improve the sustainable utilization of soil.

Abstract:The purpose of this study was to explore the influence of dripper discharge and slope factors on vegetation-concrete moisture migration by using composite artificial soil. The dynamics of wetting front of vegetation concrete and spatial-temporal distribution of soil moisture under buried drip irrigation in soil were studied, and the similarities and differences of moisture transfer between vegetation concrete and natural soil were discussed as well, which could provide theoretical reference for irrigation scheduling of drip irrigation during ecological restoration of high-steep slope. The results showed that dripper discharge rate and slope had the greatest influence on vertically upward moisture migration, but had little impact in horizontal direction. At the earlier stage of irrigation, the influence of soil matrix suction was much greater than that of gravity, and the vertically upward distance of moisture migration was similar to the horizontal distance. During the middle period, the infiltration rate in vertically upward and horizontal directions decreased with the increases of slopes. At the later stage, the vertically downward migration rate gradually tended to be stable, which was mainly induced by gravity. At the same irrigation volume, the smaller the flow rate, the farther the wetting front would migrate. During the period of moisture redistribution, the distance of vertically downward migration was the farthest, followed by horizontal direction, and vertically upward distance was the nearest. The contours of moisture content were oval, and vertically downward moisture content were larger than those in vertically upward and horizontal direction. Both power and quadratic functions could fit the relationship between the distance of wetting front migration and infiltration time, of which power function was better(R²>0.95), but R² was slightly smaller than that of natural soil, which expanded the application scope of Soil Hydrodynamics in the composite soil.

Abstract:Based on daily meteorological data from 14 national meteorological stations inside and outside the Jinghe River Basin from 1971 to 2019, the standardized precipitation evapotranspiration indicators (SPEI) were obtained using the precipitation and potential evapotranspiration data at different time scales. Through the inverse distance weighted interpolation (IDW) and Mann-Kendall trends Test, Morlet wavelet analysis and other methods, the temporal and spatial evolution characteristics of drought in the Jinghe River Basin were analyzed. The results showed that in the past 50 years, the Jinghe River Basin was generally arid, but the drought degree had been reduced. The seasons drought events occurred possibly was autumn>spring>summer>winter. The annual drought had an abrupt change in 2011, while the spring, autumn and winter droughts mutated significantly respectively in 1994, 2010, and 1996 (P<0.05). The number of persistent drought events spanning summer and autumn occurred the most, and the probability of persistent drought events in autumn was the greatest. These findings are of great significance for the early warning of drought resistance and agricultural development in the Jinghe River basin.

Abstract:This paper aimed to study the changing laws and differences of soil conservation functions of Pinus tabulaeformis forests with different densities in the loess area of western Shanxi Province, and to evaluate their soil conservation function, so as to strengthen forest stand management and ecological restoration. Four kinds of P. tabulaeformis plantations with different densities (925 plant/hm², 1 325 plant/hm², 1 750 plant/hm² and 2 250 plant/hm²) in the Caijiachuan watershed of Jixian County, Shanxi Province were taken as the research objects. The soil bulk density, porosity and other physical properties, organic matter and other chemical properties as well as the amount of slope runoff and sediment were measured and analyzed, and 12 evaluation indicators were determined, and the entropy weight method (EWM) was used to evaluate comprehensively the soil conservation functions of each P. tabulaeformis forests. The results showed that:(1) There were significant differences in soil bulk density, total porosity, non-capillary porosity, capillary porosity, total nitrogen, total phosphorus, ammonia nitrogen, nitrate nitrogen and available phosphorus among the four kinds of P. tabulaeformis plantation (P<0.05). (2) The change of stand density would change the 12 indicators of soil physical properties, soil nutrients and runoff and sediment volume of the P. tabulaeformis forest. Among them, soil bulk density, runoff and sediment volume all decreased first and then increased with the increasing of forest density. Soil organic matter, total nitrogen, total phosphorus, nitrate nitrogen and available phosphorus showed the opposite tendency with the increasing of forest density. (3) The soil physical structure, soil fertility, runoff and sediment yield of different P. tabulaeformis forests all showed certain change laws with the change of density. The improvement of soil structure and soil fertility increased first and then decreased with the increasing of forest density. With the increasing of forest density, the amount of runoff and sediment decreased first and then increased. (4) The evaluation of soil conversation function of P. tabulaeformis plantations with different densities showed that the soil conservation function of P. tabulaeformis forest increased firstly and then decreased with the increasing of density. The conservation soil function of P. tabulaeformis forest land with a density of 1 750 plant/hm² was relatively good. From the perspective of soil conservation, it was recommended that 1 750 plant/hm² should be used as the management density of P. tabulaeformis plantations in the loess area of western Shanxi. This density could better maintain water and soil and improve the soil quality of forest land.

Abstract:To understand changes in the ecological environment and its main driving forces in the ecologically fragile areas of the Loess Plateau in the past 20 years since the implementation of the "Grain for Green" Program, taking Yulin City as a typical example of the fragile ecological environment on the Loess Plateau, The vegetation coverage of Yulin City from 2001 to 2020 was estimated based on the pixel dichotomy model. This study analyzed the spatial and temporal variations of the vegetation coverage in Yulin City during the past 20 years by using univariate linear regression methods. The dominant factors affecting the interannual changes and spatial distribution of vegetation coverage were analyzed by using the partial correlation analysis and geographic detector methods during the different periods of "Grain for Green" Program. The results showed that:(1) The vegetation coverage in Yulin City significantly increased with time series (S=0.011, p<0.01) from 2001 to 2020. The vegetation coverage during the construction period (2001-2010) increased significantly (S=0.013, p<0.01), while its increasing trend in the consolidation period (2011-2020) was not significant (S=0.005, p>0.05). (2) The spatial distribution of vegetation coverage in Yulin City decreased from east to west from 2001 to 2020. The vegetation coverage of all counties (districts) in Yulin City showed an overall increasing trend, among which the eastern part of Yulin City had a more significant growth trend. However, the proportion of area with increasing vegetation coverage in Yulin City in the construction period (82.1%) was larger than that in the consolidation period (58.0%). (3) From 2001 to 2020, the dominant factors affecting inter annual change of vegetation coverage were the cumulative area of the Grain for Green Program and rainfall. The cumulative area of the Grain for Green Program was the primary factor in the construction periods, while rainfall was the primary factor in the consolidation period. (4) Soil texture, rainfall and land use type mainly affected the spatial distribution of vegetation coverage from 2001 to 2020. During construction and consolidation periods, the spatial differences of soil texture were closely related to spatial stratified heterogeneity in the vegetation coverage. The spatial heterogeneity of vegetation distribution and the interaction between the main influencing factors could provide a scientific basis for the precise implementation of ecological restoration measures.

Abstract:Based on the precipitation data of 13 meteorological stations in Qujiang Basin from 1961 to 2020, this study used cumulative anomaly, Mann-Kendall test, wavelet analysis, and Kriging interpolation methods to analyze spatio-temporal characteristics of precipitation and extreme events variations. The results showed that the 60-year average annual precipitation was 1 126.17 mm in the Qujiang basin, giving a slow upward trend with a tendency rate of 6.9 mm/10 a. The annual precipitation fluctuated violently, with cyclical changes of 27 a and 15 a. The average annual precipitation increased from the west to the northeast. The area with high precipitation was located in the Wanyuan area in the northeast of the basin, while the area with low precipitation in the western Bazhong area. The annual precipitation tendency rate increased from the northwest to the southeast, and the precipitation tendency rate in the east and south was 10~15 mm/10 a. Precipitation in the Qujiang Basin changed seasonally, with a downward trend in spring and autumn, and an upward trend in summer and winter. The 5-year sliding average indicated that the summer tendency rate was 16.9 mm/10 a, but -7.7 mm/10 a for the autumn. Seasonal precipitation fluctuated significantly with many mutation points. The mutation points in spring, summer and autumn were mainly concentrated in 1961-1980 and 2010-2020, and the mutation points in winter concentrated in 1985-2005. The highest precipitation tendency rates in spring, summer, autumn, and winter were in the south, northeast, southeast and west of the basin respectively. Heavy rainstorm days in the Qujiang basin during the flood season averaged 4.28 days per year, showing an upward trend with a rate of 0.21 d/10 a in the studied 60 years. During the flood season, it fluctuated significantly, and there was a significant increase tendency in 1965, 1983 and 1984. Heavy rainstorm days in the flood season had the periodic changes of 14 a and 21 a. The multi-year average of heavy rainstorm days showed an increasing trend from the southwest to the northeast. The upward trend in the southern part of the basin-Dachuan area was the fastest, which was 0.15 d/10 a higher than the average upward trend of the whole basin.

Abstract:In order to find a method that can estimate the soil evaporation of gravel-mulched land in arid regions of central Ningxia effectively, the relationship between soil water evaporation ratio and surface soil water content under six sand-soil mixing ratios of 0 (S1), 20% (S2), 40% (S3), 60% (S4), 80% (S5), and 100% (S6) was studied, and the estimation model of soil evaporation of gravel-mulched land was constructed by setting up micro-lysimeters. The results indicated that the soil water evaporation ratio changed in stages with the surface soil water content, that was, S2~S6 had two stages, S1 had three stages, and there was a certain lag in the second and third stages of S1 compared with other treatments. The critical value of surface soil water content could be expressed as θ_si=0.0030s_i²-0.1705s_i+14.7340; The first and second stages of soil evaporation of S1~S6 could be expressed as E_s=E₀(a_iθ_i+b_i) and E_s=E₀(a_iθ_i²+b_iθ_i+c_i), respectively, (the second and third stages of S1 were E_s=E₀(a_iθ_i²+b_iθ_i+c_i)), and the overall accuracy was above 85%. Based on the above, the quadratic paraboloid model and polynomial model were constructed in two stages by further integrating water surface evaporation, surface soil water content, and sand-soil mixing ratios. The reliability of the model was high, and it could provide reference for local water resources management.

Abstract:The Loess Plateau has always been one of the most serious soil erosion and environmental problems regions in China. Artificial vegetation restoration can effectively improve soil properties and soil quality, therefore clarifying the responses of soil moisture and nutrient properties to long-term artificial vegetation restoration is conducive to further effectively improving the eco-environment. This study selected three typical vegetation types, including natural restoration secondary forest land, artificial Robinia pseudoacacia forest land and artificial Pinus tabulaeformis forest land, during ecological restoration in the loess region of western Shanxi. By measuring soil physical properties, soil moisture contents and soil nutrients such as organic carbon, nitrogen, phosphorus and potassium contents, the differences under the long-term artificial vegetation restorations were comparatively analyzed. The results showed that:(1) The soil bulk density of secondary forest land, Robinia pseudoacacia forest land and Pinus tabulaeformis forest land in 0-20 cm shallow layer was 1.15, 1.04 and 1.06 g/cm³, respectively. The soil bulk density increased with the increase of soil depth. (2) The soil moisture of secondary forest land in shallow layer was better than those of Robinia pseudoacacia forest land and Pinus tabulaeformis forest land. When soil moisture consumption period (before the start of growth season) transited to the accumulation period (at the beginning of the growth season), the dynamic variations of soil moisture in secondary forest land were more dramatic. (3) The soil carbon storage in secondary forest land was higher, while the soil nitrogen and phosphorus storage in Pinus tabulaeformis forest land was higher. The vertical variations of soil nutrients of the three forest lands had significant differences with accumulation in surface layer. The contents of organic carbon, total nitrogen, total phosphorus, available nitrogen and available potassium all decreased with the increase of soil depth, while the contents of available phosphorus increased first and then decreased. Considering the soil moisture and nutrient condition, it was suggested that the secondary forest should be mainly conserved in the process of vegetation restoration to achieve the better water and carbon storage and other ecological benefits, which would be conducive to the optimization of stand management, and the promotion of vegetation restoration and ecological construction in the western Shanxi loess region.

Abstract:To investigate the differences of nutrient status and carbon (C) sequestration capacity between mixed forests and pure forests, the pure forests of Robinia pseudoacacia, pure forests of Pinus tabuliformis, mixed forests of Robinia pseudoacacia and Pinus tabuliformis, and mixed forests of Robinia pseudoacacia and Populus davidiana, located in Loess Hilly and gully region of China, were taken as the objects. Through the field investigation and indoor analysis, the ecological stoichiometry and C storage of the pure and mixed forests ecosystems were studied. The results showed that:(1) Compared with the pure forests, the mixed forests of Robinia pseudoacacia and Pinus tabuliformis significantly increased the C contents of branches and roots, the phosphorus (P) contents of leaves and trunks, the C:P and N:P ratio of branches of Robinia pseudoacacia species, and also significantly increased the nitrogen (N) contents of leaves, branches and roots and the N:P ratio of branches, trunks and roots of Pinus tabuliformis species, but significantly decreased the C:N ratio of all organs of Pinus tabuliformis species, while the mixed forests of Robinia pseudoacacia and Populus davidiana only significantly increased the P content of branches of Robinia pseudoacacia. (2) The content of soil C in the mixed forests of Robinia pseudoacacia and Pinus tabuliformis was significantly higher than that of the pure Robinia pseudoacacia forests, and the content of soil P was significantly lower than that of the pure Pinus tabuliformis forests. The differences of P in the soils between the mixed forests of Robinia pseudoacacia and Populus davidiana and the pure forests of Robinia pseudoacacia were not significant. (3) There was a significant correlation between the leaf and litter C contents in two pure forests. And the C:N, C:P ratios of the total pure forests were significantly correlated between tree leaf-litter-soil; but in total mixed forests, only P contents in litter and soil were significantly correlated with C:P ratio. (4) The C storage in tree layer of mixed forests of Robinia pseudoacacia and Populus davidiana was significantly higher than that of the pure Robinia pseudoacacia forests, and the C storage in understory vegetation layer and soil layer of mixed forests of Robinia pseudoacacia and Pinus tabuliformis was significantly higher than those in the pure Robinia pseudoacacia forests. This study could not only lay a foundation for an in-depth understanding of the nutrient cycle mechanism in the Loess Plateau, but also provide a theoretical basis for the management of plantation in the Loess Plateau.

Abstract:A pot experiment was conducted to investigate the effects of biochar (BC) amendment (0, 12, 36 t/hm²) on soil organic carbon (SOC) and its fractions in a Cunninghamia lanceolata seedling under different simulated levels of nitrogen (N) deposition (0, 40, 80 kg/(hm²·a) N) for 18 months. The results indicated that compared with the control, BC amendment significantly increased the contents of SOC, recalcitrant pool of carbon (RPC), and dissolved organic carbon (DOC) by 40.1%~99.2%, 104.0%~267.8% and 75.3%~194.7% under different levels of N deposition (P<0.05), respectively. Meanwhile, the proportion of labile C from acid hydrolysis (LPC) in SOC decreased significantly by 28.8%~53.3%, and the proportion of RPC in SOC increased significantly by 45.7%~84.6% in the treatments of BC amendment combined with N deposition (P<0.05). The effects were the most significant when higher-rate BC was applied alone (P<0.05). No significant differences were found in the content of LPC in the treatments of BC amendment alone or simulated N deposition alone, whereas LPC was significantly reduced under the higher BC amendment combined with simulated N deposition (P<0.05).The higher rate of simulated N deposition alone significantly decreased soil microbial biomass carbon (MBC) content and the proportion of MBC in SOC, but had no significant effect on the DOC content and the proportion of DOC in SOC. However, the interaction of simulated N deposition and higher rate of BC significantly increased the proportion of DOC in SOC (P<0.05). Correlation analysis suggested that soil pH and available nutrients (AP, AK) were positively correlated with SOC, RPC and DOC contents, and were significantly negatively correlated with LPC (P<0.01). Our results indicated that the interaction between simulated N deposition and BC amendment has the greatest impact on RPC fraction, which is conducive to improving the stability of SOC fractions and increasing soil C storage in the short term.

Abstract:Forest soil and water conservation benefits include water conservation capacity and soil erosion risk. The purpose of this study was to explore the influence of stand factors on soil erosion based on slope scale, and further reveal the soil and water conservation benefit mechanism of forest vegetation. Water conservation capacity and soil erosion factors of Pinus taiwanensis forest and Cunninghamia lanceolata forest were calculated by ring knife method and EPIC model. The results showed that:(1) There was no significant difference in soil bulk density of P. taiwanensis forest in vertical section, ranging from 0.66 to 1.10 g/cm³. The bulk density of Chinese fir forest (0.92~1.21 g/cm³) showed that the lower layer (40-80 cm) was greater than the upper layer (0-40 cm). The maximum water holding capacity of the upper layer (0-20 cm) of P. taiwanensis forest was significantly higher than that of C. lanceolata forest. Soil capillary water holding capacity, total porosity, capillary porosity only in 10-20 cm soil layer showed that P. taiwanensis forest was greater than C.lanceolata forest. (2) The range of soil saturated water storage was 51.92~59.07 mm (P. taiwanensis), 48.44~54.78 mm (C. lanceolata), 10-20 cm soil layer of P. taiwanensis was significantly greater than C. lanceolata (59.07 mm>48.87mm, P<0.05, respectively). The maximum water storage capacities of soil were consistent. (3) Only in the 10-20 cm soil layer, the clay content and silt content of P. taiwanensis (0.44%, 15.43%) were significantly higher than those of C. lanceolata (0.19%, 9.6%), and the soil particle size distribution in the other soil layers had no significant difference. (4) The soil sensitivity showed no significant difference between the two stands in the soil depth of 0-80 cm (P>0.05). Based on the above water conservation capacity indicators, it was found that the soil of P. taiwanensis forest had more advantages, but there was no significant difference in soil erosion sensitivity between the two. Planting P. taiwanensis on suitable sites could better play the role of soil and water conservation.

Abstract:Took Qinghai spruce (Picea crassifolia) in the small watershed of Pailugou in the central Qilian Mountains as the research object. From May to October 2018, the radial growth process of four strains of Qinghai spruce was measured using the belt tree radial growth recorder, and the meteorological factors were simultaneously measured. Based on the soil temperature and humidity, the seasonal variation characteristics of the radial growth of individual Qinghai spruce and the differences between trees were analyzed, and the limiting factors of Qinghai spruce in different growth stages were also determined. The results showed that:(1) The four Qinghai spruce plants began to grow on June 8 and ended on July 28, with a growth period of about 51 days. (2) The characteristics of the radial growth season of Qinghai spruce were different among individuals. The growth of trees with smaller DBH (DBH=10.0 cm and 11.0 cm) started later and ended earlier, resulting in the shorter growing period and less annual cumulative growth, while trees with larger DBH (DBH=18.3 cm and 21.0 cm) gave an opposite results, with a longer growing period and more annual cumulative growth. (3) The radial growth of Qinghai spruce had an obvious seasonal change pattern, which was divided into three stages:the initial growth stage (May to early June), the rapid growth stage (early June to late July) and the end growth stage (August to October) with the average growth rates of 0.35 μm/d, 12.99 μm/d and 0.54 μm/d respectively. (4) The limiting factors of Qinghai spruce growth were different among different growth stages:in the initial growth stage, rainfall and soil temperature were the main factors restricting growth, and during the rapid growth stage, rainfall and soil volumetric water content were the main factors. Therefore, from the perspective of the entire growing season, soil temperature and moisture were the main factors affecting the annual radial growth of Qinghai spruce.

Abstract:It is necessary to explore the effects of saline water irrigation combined with application of organic fertilizer on water-stable aggregates of plow layer soil. In this study, a long-term saline water irrigation experiment combined with application of organic fertilizer was carried out under winter wheat-summer maize double cropping system. Treatments were set up with four irrigation water salinities (1, 2, 4, 6 g/L) and with organic fertilizer applied (OF) or not (NOF). We measured the effects of different treatments on variation of soil salinity (EC_1:5), soil organic matter (SOM) content and the stability of water-stable aggregates in 0-20 cm soil layer form 2018 to 2019. The results indicated that saline water irrigation tended to increase soil salinity and decrease SOM content and the stability of water-stable aggregates. Meanwhile, with the increasing salinities of irrigation water, SOM content and the mass fraction of water-stable aggregate (>0.25 mm) (WR_0.25), mean weight diameter (MWD) and geometric mean diameter (GMD) decreased; on the contrary, soil EC_1:5 and fractal dimension (D_m) increased. In addition, there were significant differences only between 4 g/L, 6 g/L and 1 g/L treatments. It was found that applying organic fertilizer could reduce EC_1:5 in 0-20 cm soil layer. When the salinity of irrigation water was ≥ 2 g/L, the EC_1:5 of plow layer with organic fertilizer application was 4.64%~48.29% lower than those of treatments without organic fertilizer application. Applying organic fertilizer significantly increased SOM content, WR_0.25, MWD and GMD, with the increases of 80.75%~127.32%, 10.36%~90.44%, 12.90%~129.11% and 11.88%~81.57%. In summary, irrigation water salinity of ≥ 4 g/L could significantly increase soil salinity, reduce organic matter content and destroy soil aggregate structure, so it should be used cautiously. The application of organic fertilizer could promote the salt leaching from the surface soil to the deep layer, reduce the negative impacts of salt on soil environment, and contribute to the safe and efficient utilization of saline water resources.

Abstract:In order to clarify the characteristics of nitrogen and phosphorus and influencing factors in water-soil-plant system in the riparian zone of the Sunxi River watershed, Chongqing, the descriptive statistics, cluster analysis, correlation analysis and redundancy analysis were carried out to study the characteristics of nitrogen and phosphorus content and spatial distribution in water, soil and plants in the riparian zone of the small watershed at the end of the Three Gorges Reservoir, as well as to study the correlation between nitrogen and phosphorus in each sphere and the factors influencing nitrogen and phosphorus in water. The results showed that:(1) The riparian zone was affected by the river section. From upstream to downstream, the content of nitrogen and phosphorus in water and soil total nitrogen decreased first and then increased, while the content of nitrogen and phosphorus in the plant, soil nitrate nitrogen, total and available phosphorus gradually increased. There existed an obvious agricultural nitrogen input in the downstream. (2) The total nitrogen content in water was significantly positively related to the nitrogen content in different vegetative organs of plant (P<0.01). Total phosphorus content in water was significantly positively related to soil total and available phosphorus content (P<0.001), and both soil total and available phosphorus content were significantly negatively related to altitude (P<0.001). (3) The content of nitrogen and phosphorus in riparian water were affected by the content of soil nitrogen and phosphorus, plant nitrogen and phosphorus and topography, and among them, soil nitrogen and phosphorus were the dominant factors. The permutation test of available phosphorus at soil depth of 20-40 cm, available phosphorus at 0-20 cm, total phosphorus at 20-40 cm, total phosphorus at 0-20 cm and nitrate nitrogen at 0-20 cm were all significant (P<0.05), with the variation interpretation rate of 25.11%, 21.71%, 11.14%, 8.13% and 3.05%, respectively. The river section had an impact on the content of nitrogen and phosphorus in the water, soil and plants in the riparian zone. From upstream to downstream, nitrogen and phosphorus gradually accumulated, but the difference decreased. Nitrogen and phosphorus in water, soil and plants had a certain correlation with each other, and were also affected by altitude, slope and aspect. Cultivated land was the main cause of agricultural non-point source pollution in the lower reaches of the river basin. It was necessary to strengthen the ability of plant protection and soil conservation in the middle and lower reaches, and to optimize the land use pattern in the riparian zone, so as to provide a basis for agricultural non-point source pollution control in small watersheds in the Three Gorges Reservoir area.

Abstract:A field experiment was conducted to investigate the effects of reductive soil disinfestation (RSD) and biochar (BC) application on dissolved organic matter (DOM) in degraded vegetable soils. In this study, six treatments, i.e., (1)soil untreated (CK), (2) soil incorporated with 1% (w/w) biochar (BC), (3) soil flooded (SF), (4) soil flooded and covered with plastic film (SFF), (5) soil incorporated with 1% (w/w) alfalfa residue, flooded and covered with plastic film (RSD), and (6) soil incorporated with 1% (w/w) alfalfa residue and 1% (w/w) biochar, flooded and covered with plastic film (RSD+BC) were performed to compare the effects of different treatments on DOM content and its spectral characteristics in soil 0-20 cm and 20-40 cm of layers. The results showed that for 0-20 cm soil, compared with CK, soil pH value of other treatments was increased significantly, and NO₃^--N contents of BC, SF, SFF, and RSD treatments were significantly decreased by 31.9%, 59.4%, 40.0%, and 22.3%, respectively. Soil dissolved organic nitrogen (DON) content was significantly increased by RSD treatment (P<0.05). The contents of dissolved organic carbon (DOC) in RSD and RSD+BC treatments were significantly increased by 188.2% and 201.4% (P<0.05), respectively, whereas the degree of DOM aromatization and humification was decreased under the two treatments. Soil DOM was mainly composed of fulvic acid-like and humic acid-like material, and the fluorescence intensity of DOM in RSD+BC treatment reached the maximum. For 20-40 cm soil, the fluorescence intensity and DOC contents of all treatments were decreased significantly compared with that of 0-20 cm soil. However, compared with CK, the DOC contents in RSD and RSD+BC treatments were still increased significantly (P<0.05), while the DON contents in BC and RSD+BC treatments were decreased. These results implied that the combination of biochar and RSD could further alleviate soil acidification in the short period, improve soil DOC content, and reduce the degree of soil DOM aromatization and humification. This study provides scientific guidance for the remediation and environmental risk assessment of degraded facility vegetable soil.

Abstract:To explore the effects of long-term different fertilization treatments on organic carbon fractions and hydrolase activities related to carbon cycle of purple soil under rice wheat rotation in Southwest China, this work was based on the long-term fixed-point experiment of 29-years rice wheat rotation in purple soil of Beibei in Chongqing. Five treatments were applied to determine the contents of soil organic carbon fractions and the activities of hydrolases related to soil carbon cycle including no fertilization (CK), single application of NPK, combined application of organic and inorganic fertilizer (NPKM), straw returning with chlorinated fertilizer ((NPK) _ClS), and straw returning with inorganic fertilizer (NPKS).Their correlations were further analyzed accordingly. Results showed that long-term fertilization (NPK, NPKM, and NPKS) significantly increased soil total organic carbon and different fractions of organic carbon content, the total organic carbon content of each fertilization treatment was enhanced by 11.6%~40.2% when compared with CK. Amongst them, NPKS treatment exhibited the most significant improvement effect. Coarse particle organic carbon (cPOC), particle organic carbon within microaggregates (i_POC), silt and clay particles organic carbon within macroaggregates(M_s+c) showed significant positive correlation with total organic carbon content. Notably, cPOC were the most sensitive to the change of soil carbon pool, 0.4 unit of soil organic carbon was stored in cPOC for each unit increase of soil organic carbon. In the three major organic carbon pools of chemical protected, unprotected, and physically protected, the chemical protected organic carbon pool was the main fractions of organic carbon in purple soil, accounting for 66.1% on average. The distribution of soil organic carbon in different carbon pools was affected by fertilization, as compared to CK, the distribution proportion of unprotected and physically protected organic carbon in soil treated with NPKM and NPKS was significantly improved, with an increased rate of 10.1%~24.1%. Moreover, ferlilization significantly increased hydrolase activities related to carbon cycle. The activities of α-glucosidase (AG), β-glucosidase (BG), and β-xylosidase (BDX) in soil treated by NPKM and NPKS were enhanced by 14.5%~89.1% in comparison with CK, and were the best enhanced enzymes. There was a significant positive correlation between hydrolase activities (AG, BG and BDX)and unprotected soil. In conclusion, the combined application of organic and inorganic fertilizer is the best fertilization measure to improve soil organic carbon content and hydrolase activities related to the soil carbon cycle.

Abstract:Losses of nutrients, water and soil was serious in black soil sloping farmlands in Northeast China, and the soil organic carbon (SOC) decreased year by year due to soil erosion and conventional longitudinal ridge-tillage. However, the characteristics of water and soil losses, and the changes in soil organic carbon under different tillage methods remain unclear. This study explored the impact of longitudinal ridge-tillage and cross-ridge tillage practices on losses of water and soil, and the changes in SOC from sloping farmland based on field experiments. Results showed that:(1) Compared with the longitudinal ridge-tillage, cross-ridge tillage significantly reduced the surface runoff and sediment losses by 97.1% and 93.1%, respectively, showing a strong interception of surface runoff and sediment. (2) The cross-ridge tillage could reduce the losses of SOC and dissolved organic carbon (DOC) from the sloping farmland by 99.9% and 99.3%, respectively, and shoulder and back of the slope were two main positions of SOC sequestration, where 98.8% of SOC and 94.4% of DOC were sequestrated. (3) The cross-ridge tillage significantly increased the yield of spring maize, especially at the shoulder (by 21.2%) and back (by 19.4%) positions (both p<0.05), based on a 3-year cross-ridge tillage. Therefore, compared with the conventional longitudinal ridge-tillage, the cross-ridge tillage is a multi-win practice to reduce soil erosion and SOC losses, and increase the productivity, which can serve as a conservation measure for the protection of black soil sloping farmlands in Northeast China.

Abstract:The purpose of this study was to investigate the changes in soil microbial biomass and enzymes activities during the decaying of Salix psammophila sand barriers. The sand barriers which had been laid for ten years were used as the research object. The research methods included field in-situ sampling and laboratory tests. Combined with RDA data sequencing analysis, the main environmental factors affecting soil microbial biomass and enzymes activities were revealed. The results showed that the values of C:N and C:P in soil increased with the increase of laying years. The C:N value in 10 years was 16.14 times of that in one year, while the N/P decreased by 83.96% after 10 years. The soil MBC, MBN and MBP increased firstly and then decreased with the decaying, and reached the maximum value in the 7th year, which was 2.67, 2.18 and 1.43 times that in the 1st year, respectively. With the increase of decaying years, the activity of soil alkaline phosphatase increased first and then decreased. It peaked in the 6th year and showed a significant difference (P<0.05), but the activities of urease and sucrose in one year were significantly higher than those in others (P<0.05). The RDA analysis showed that the sequences of the major soil physical and chemical factors affecting soil microbial biomass and enzymes activities were as follows:available potassium>water content>C:N ratio>alkaline hydrolysable nitrogen>pH>available phosphorus>N:P ratio>C:P ratio. The main driving factors were soil available potassium and water content. The results of this study could provide an important theoretical basis for the study on soil carbon, nitrogen and phosphorus cycling in the desert ecosystem.

Abstract:This study was aimed to select suitable crop rotation system by exploring the effect of the different crop rotation systems on soil available nutrients and wheat yield in Fluvo-aquic soil in Huang-Huai Plain. A field experiment was conducted with five treatments:(1) continuous annual wheat-maize (WM-WM-WM), (2) annual wheat-maize+annual wheat-soybean alternately (WM-WS-WM), (3) annual wheat- maize+annual wheat-peanut (WM-WP-WM), (4) continuous annual wheat-peanut (WP-WP-WP), (5) continuous annual wheat-soybean (WS-WS-WS). The results showed soil available nutrients decreased generally with soil depth under all treatments. The different of alkali-hydrolyzed nitrogen (AN) content in different soil layers was higher with time among treatments. The AN contents in 0-20 cm soil layer under WM-WP-WM and WP-WP-WP were higher. The nitrate nitrogen (NO₃^--N) and ammonium nitrogen (NH₄⁺-N) contents in 0-20 cm under WP-WP-WP and WS-WS-WS were higher, and with the highest as 43.98 mg/kg and 17.58 mg/kg under WP-WP-WP. The available phosphorus (AP) content and available potassium content under WP-WP-WP were higher, with the highest value as 24.49 mg/kg and 172.80 mg/kg, respectively. Both crop rotation system and soil depth affected NO₃^--N, NH₄⁺-N, AN, AP and AK. The grain protein content of wheat under WP-WP-WP changed significantly with time, with the highest value as 17.83%. The highest wheat biomass and yield were found under WP-WP-WP and WS-WS-WS. Moreover, there was a positive correlation between wheat N harvest index and wheat harvest index. The WP-WP-WP treatment increased the number of grains (34.2/ear), and the WS-WS-WS treatment increased the number of wheat (267 000 ears/hm²). During the experimental period, in the Fluvo-aquic soil in Huang-Huai Plain, the contents of soil AN, NO₃^--N, NH₄⁺-N, AP, above ground biomass and grain protein were increased under WP-WP-WP. The NH₄⁺-N content was increased under WS-WS-WS. Meanwhile, the highest wheat yield was obtained under WS-WS-WS and WP-WP-WP. Therefore, the wheat-peanut and wheat-soybean rotation models were suggested as the optimum crop rotation system in this area.

Abstract:In response to the problems of natural grassland degradation, serious soil erosion, and low productivity of artificial grassland in arid steppe region of Northwest China, effects of planting patterns, water and nitrogen regulation on forage yield, quality and water and nitrogen use efficiency were investigated in order to obtain a high-yielding and high efficiency grassland management pattern. In this study, triennial alfalfa and Bromus inermis (sown in 2018) were used as experimental materials to analyze planting patterns (mixed alfalfa and B. inermis, unicasted B. inermis; namely D1, D2), the amount of nitrogen application (N 60 kg/hm², 120 kg/hm²; namely N1, N2), and irrigation water gradient (calculated by the percentage of irrigation water limit to the field water holding capacity, light deficit 65% θ_f, moderate deficit 55% θ_f, severe deficit 45% θ_f, recorded as W1, W2, W3, the upper limit of irrigation is 85% θ_f) on forage yield, quality and water and nitrogen use efficiency. The results showed that:(1)Increasing irrigation amount and nitrogen application rate was beneficial to the growth of plant height and stem diameter. Compared with W3N1 treatment, the average plant height of mixed alfalfa and B. inermis, unicasted B.inermis increased by 27.41% and 20.26%, 26.55%, and stem diameter increased by 11.32% and 4.11%, 20.98% under W1N2 treatment, and mixed forage had a promoting effect on B. inermis plant height and a suppressing effect on stem diameter. (2) The increase of irrigation amount and nitrogen application rate was beneficial to improve the forage yield and quality. The annual yield and crude protein (CP) content of forage under W1N2 treatment were the highest, and compared with W3N1 treatment, the annual yield and CP content of mixed forage increased by 42.16% and 27.00%, and unicasted forage increased by 38.59% and 37.26%. Respectively, ADF and NDF of mixed forage decreased by 19.56% and 33.86%, and unicasted forage decreased by 21.29% and 25.53%. (3) With the increase of irrigation amount, IWUE and WUE decreased, while PFP_N increased. With the increase of nitrogen application rate, IWUE, WUE and PFP_N decreased in mixed forage, while IWUE and PFP_N decreased and WUE increased in unicast forage. Based on the principal component analysis, the highest combined score of light deficit (irrigation lower limit:65% θ_f) and high nitrogen (120 kg/hm²) was obtained in the mixed forage, which was a suitable water and nitrogen management pattern in the region. This result can provide a theoretical basis for forage planting management in arid and semi-arid grassland region of Northwest China.

Abstract:This study aimed to investigate the effects of rice straw-derived biochar application on rice grain yield, nitrogen use efficiency (NUE), and fate of fertilizer N. A pot experiment was conducted to assess the effects of rice straw-derived biochar application on rice biomass, N accumulation, as well as fate of urea-N using ¹⁵N tracing method and ammonia oxidizers. Five treatments were included:no N application (N0), chemical fertilizer application only (CF), CF+0.5% biochar (BC1), CF+1% biochar (BC2), and CF+2% biochar (BC3). The results showed that BC2 and BC3 treatments significantly increased rice grain yield by 19.3% and 22.0%, compared to CF treatment, respectively. Application of biochar significantly enhanced the N accumulation of rice and N apparent use efficiency compared to CF treatment. The fertilizer N uptake by grain and rice plant was 18.6%~23.4% and 18.5%~26.5% greater in biochar application than in CF treatment, respectively. While, no significant difference was observed in the soil N uptake by grain between BC treatments (BC1, BC2, and BC3) and CF treatment. The ¹⁵N use efficiency was 30.4%, 28.5%, and 29.3% in the BC1, BC2, and BC3 treatments, respectively, which were all significantly higher than that in CF treatment (24.1%). Application of straw-derived biochar increased the fertilizer N residual in soil and reduced the N loss, compared to CF treatment. Thus, the ratio of fertilizer N loss was greatly lower in BC treatment (25.7%~27.5%) than in CF treatment (38.4%). Higher application of biochar (BC3) significantly decreased the AOB amoA gene copies, compared to CF treatment. While, no significant difference was found in AOA abundance between the BC and CF treatments. Overall, application of rice straw-derived biochar is an effective practice to increase rice yield and NUE, and reduce the N loss in the rice production.

Abstract:Taking sandy soil, fluvo-aquic soil and Shajiang soil in Dagu River Basin of Qingdao as research objects, the indoor soil column experiments was carried out to study the effects of soil temperature, pH, water content and other physical and chemical properties and combined application of biochar and nitrogen fertilizer on leaching of soil available phosphorus (Olsen-P) and total phosphorus (TP), so as to provide reference basis for improving soil phosphorus availability and reducing total phosphorus leaching. The results showed that the soil phosphorus availability was the highest when the pH was neutral or weakly alkaline, and the total phosphorus leaching loss was larger when the pH was weakly acidic. The Olsen-P content in different soil layers of the three soils showed different changes with the increasing of water content. The phosphorus availability of the three soils increased gradually with the increasing of temperature, while the leaching loss of total phosphorus decreased with the increasing of temperature. The combined application of biochar and nitrogen fertilizer (T1~T7) could effectively improve the availability of soil phosphorus, and the effect followed the order of combined application of biochar and nitrogen fertilizer> single addition of biochar> single addition of nitrogen. When the ratio of nitrogen fertilizer to biochar was 2:1, the availability of soil phosphorus was the highest. The inhibition effect of biochar combined with nitrogen fertilizer on soil total phosphorus leaching was better than that of biochar alone, and the inhibition effect of nitrogen fertilizer on soil total phosphorus leaching was not obvious.

Abstract:In order to explore the difference of phosphorus accumulation and loss risk of different organic fertilizers in the process of reclaiming the soil in the mining area. In this experiment, the reclaimed soil of coal mining collapse in Xiaoyi City, Shanxi Province was taken as the research object, and the effect of different organic fertilizers, including poultry manure, swine manure,cow manure and chemical fertilizer, under 4 P levels (0, 25, 50, 100 kg/hm²) after 4 years in reclaimed soil of mining area on total phosphorus, Olsen-P, Mehlich3-P, CaCl₂-P, and degree of phosphorus saturation (DPS) and the relationship among them were studied. The results showed that:(1) The application of organic fertilizers increased the phosphorus content in the soil, and the greater the amount of phosphorus applied, the more obvious the impact on the phosphorus content, especially the total phosphorus, Olsen-P, Mehilic3-P in the soil, and CaCl₂-P increased; Compared with non-phosphorus treatment and chemical fertilizer, the application of organic fertilizers increased the surface layer (0-20 cm) soil degree of phosphorus saturation (DPS); In general, the effects of different fertilization treatments on the soil phosphorus content showed that poultry manure ≥ swine manure>cow manure>chemical fertilizer. (2) There was a significant linear correlation between the soil Olsen-P and Mehlich3-P, Olsen-P and CaCl₂-P, Mehlich3-P and CaCl₂-P in each fertilization treatment. (3) Compared with swine manure, cow manure and chemical fertilizer treatment, poultry manure treatment had the greatest impact on the risk of phosphorus loss in reclaimed soil. When DPS ≥ 39.31%, Olsen-P ≥ 26.24 mg/kg and Mehlich3-P ≥ 49.06 mg/kg, the content of CaCl₂-P in soil increased rapidly. Therefore, the above indexs could be used as the critical value of phosphorus loss in reclaimed soil of mining area. If these values exceed, the risk of soil P loss would increase. We need to be vigilant about the pollution of surface and underground water.

Abstract:The Liuxi River reservoir basin is a typical subtropical mountain basin, and it is of great significance to study the changing characteristics of carbon and nitrogen nutrients concentrations in this basin and its influencing factors to reveal the biogeochemical cycle of subtropical basin. Based on the field sampling of water quality, landscape topography, meteorology, land use as well as soil data, this paper explored the spatial-temporal changing characteristics and the influencing factors of the carbon and nitrogen nutrients concentrations in streams located in the Liuxi River Reservoir basin, using correlation and Elastic Net regression analysis. The results showed that:(1) The temporal trend of carbon and nitrogen nutrients concentrations in streams was relatively stable during dry period, whereas the spatial variation was obvious. (2) The slope of sub-basin was an important environmental factor that caused the changes of carbon and nitrogen nutrients concentrations in different streams, and the slope beyond 6° had a significant positive effect on the change of carbon and nitrogen nutrients concentrations. (3) The average relative humidity of the basin also significantly affected the concentrations of carbon and nitrogen nutrients in streams. The greater the relative humidity of the basin was, the higher the concentration of carbon nutrients in the streams would be, but the concentration of nitrogen nutrients would be relatively low. Compared witth the DOC, the NH₄⁺ and NO₃^- concentrations in streams were less sensitive to the weather conditions. (4) The land use, such as the proportion of the built-up area and other human activities, significantly affected the concentrations of carbon and nitrogen nutrients, as shown by a negative correlation between the built-up area and the DOC concentration. The increased forest cover could enhance the DOC and NO₃^- concentrations in streams, but had no significant effect on the NH₄⁺ concentration. (5) The different soil types also affected the concentrations of carbon and nitrogen nutrients in watersheds, the haplic acrisols had a positive effect on the NO₃^- concentration, and the aric anthrosols had a positive effect on the concentration of NH₄⁺. Overall, our results provide some useful scientific information for the protection of water resources and understanding the changes and influencing factors of carbon and nitrogen nutrients concentrations in the similar watersheds.

Abstract:The ecological buffer zone can effectively intercept and control the migration of non-point source pollutants into the water body. Alfalfa, tall fescue, sweet clover, Kentucky bluegrass and ryegrass were selected to construct a simulated ecological buffer zone. Through an artificial runoff simulation experiment, the effects of ecological buffer zone on the inhibition and control effect of fluoride ion in runoff under the different conditions, including different vegetation types, pollutant inflow concentrations, ecological buffer zone slopes and biochar types were discussed. The results showed that the ecological buffer zone of Kentucky bluegrass had the best effect on the inhibition and control of fluoride in runoff. When the flow was 0.5 L/min, the inflow concentration was 4 mg/L and the slope was 5°, the inhibition and control efficiency of fluoride concentration was 13.1% and the quality inhibition and control efficiency was 92.6%. When the flow rate was 0.5 L/min, the inflow concentration was 8 mg/L and the slope was 5°, the concentration resistance control efficiency was 20.6% and the mass resistance control efficiency was 96.4%. This means the smaller the slope, the better effect of ecological buffer zone on fluoride inhibition and control. When the flow was 0.5 L/min, the inflow concentration was 4 mg/L and the slope was 5°, the runoff inhibition and control efficiency of the ecological buffer zone was improved by adding corn straw biochar, especially the sweet clover buffer zone, whose surface runoff inhibition and control efficiency was increased by 23.8%.

Abstract:The purpose of this study was to study the influence of Pinus massoniana litter input with different densities on the soil physical and chemical properties and stand growth, and to improve the theoretical basis for selecting appropriate plantation management measures. Four planting densities, 2 500 trees/hm² (M1), 3 300 trees/hm² (M2), 4 500 trees/hm² (M3) and 6 000 trees/hm² (M4) of P. massoniana forests, were set up as research subject. The structure equation was used to explore the influence of litter input of P. massoniana forest with different densitieson soil properties. The result showed that forest density had a significant impact on litter and soil physical and chemical properties. The total storage and water holding capacity of litter were the highest under M2, which was significantly higher than others. The litter had the largest nutrient reserves of carbon, nitrogen, phosphorus, and potassium in M2, amongh which the orgainic carbon is the major, accounting for 96.98% of the total. The differences in soil physical and chemical properties decreased with the depth of the soil layer increased, and the litter layer had a greater impact on the physical and chemical properties in the surface soil. Soil water holding capacity, porosity, pH, total phosphorus, alkaline nitrogen and available phosphorus were all the highest in M2, whereas the organic matter and total nitrogen presented as M4>M2>M3>M1, and total potassium and available potassium had highest contents in M1. Litter accumulation and nutrient reserves were significantly positively correlated with soil silt, water holding capacity, porosity, organic matter, total phosphorus, and available nitrogen, while significantly negatively correlated with soil bulk density and permeability. The structural equation showed that the total storage of litter had a significantly positive correlation with soil physical and chemical properties, whereas soil water holding capacity had a significantly negative correlation with soil physical and chemical properties. Soil chemical properties had a significant positive correlation with forest volume, and a significant negative correlation was found between the forest stock and litter nutrients contents. In summary, the P. massoniana forest with M2 density had the more litter accumulation and nutrients reserves, which could reduce surface runoff, increase soil water holding capacity and porosity, reduce the loss of available nutrients, and promote root extension and extension, which should be the more appropriate forestation measures.

Abstract:The purpose of this study was to explore the effects of different saline water quality on soil salt properties and crop growth, and to provide scientific basis for saline water irrigation management. A pot experiment was carried out for cropping lettuce in the solar greenhouse. Taking the saturated solution of CaSO₄ as a control (CK), different chlorides were added to deionized water to form three saline water treatments with different cationic compositions (Na⁺, T_Na; Na⁺/K⁺ of 1:1, T_Na-K; K⁺, T_K) on the premise of the same total mole concentration added. The soil salt contents, cations contents, and photosynthetic characteristics, ions uptake and growth of lettuce were studied. The results showed that:(1) At the end of lettuce growing season (80 days after sowing, DAS), the electrical conductivity of saturated extract (EC_e) of soil at 0-20 cm depth was significantly higher than those before sowing and 50 DAS, where CK was significantly lower than others (P<0.05). The differences of soil pH values were not significant among different treatments and depths (P>0.05). At the end of the growth season, the soil salt cations mostly accumulated on the surface layer and were consistent with the salt distribution. (2) Compared with CK, single salt ion stresses (T_Na and T_K treatments) significantly reduced the photosynthetic properties, including net photosynthetic rate, transpiration rate, and stomatal conductance of lettuce (P<0.05), thus resulting in the reduced yield, where the T_Na gave the lowest yield per pot. The photosynthetic properties of T_Na-K were significantly lower than that of CK, but higher than those of T_Na and T_K, indicating that T_Na-K treatment alleviated the harm of single salt ions to the growth of lettuce. And T_Na-K increased yield compared with T_Na and T_K treatment, but without significantly difference (P>0.05). (3) Compared with CK, T_Na and T_K significantly increased the Na⁺ and K⁺ contents in the lettuce leaves, respectively; while the Cl^- content of T_Na-K treatment were higher than CK, but significantly lower than T_Na and T_K (P<0.05). The salt composition with Na⁺/K⁺ of 1:1 in saline water could maintain the ion balance of lettuce plants and alleviate the salt stress of single salt ion on lettuce growth, while as for the single ion stress, Na⁺ should cause the more stress than K⁺.