Abstract:To study the law of nitrogen loss on slope under different fertilizer types (urea, chicken manure) and different dosages (349.6, 174.8 kg/hm²), the artificial simulated rainfall test method was used to explore the reasons for the difference in nitrogen loss between the two, and to elaborate the effects of fertilizer application rate on nitrogen loss. The results showed that the slope nitrogen loss after fertilization was mainly in the form of total nitrogen loss in sediment, accounting for 78.16%~93.46%. The concentration of runoff nitrate nitrogen was higher than that of runoff ammonium nitrogen, and the loss of total nitrogen in runoff was mainly in the form of nitrate nitrogen loss. The amount accounted for 38.53%~48.62% of the total nitrogen loss in runoff. The type of fertilizer had no obvious effect on the total nitrogen concentration of the slope sediment. The nitrate nitrogen concentration and the ammonium nitrogen concentration of the silt treated with chicken manure were higher. The equal nitrogen application of chicken manure could reduce the concentration of total nitrogen, nitrate nitrogen and ammonium nitrogen in slope runoff, by 68.64%~74.23%, 70.09%~72.54%, 27.90%~39.45%, respectively. Equal-nitrogen chicken manure replacing urea could reduce the total nitrogen loss on slope surface by 11.07%~15.81%, and reduce the total nitrogen loss in runoff by 70.55%~73.36%. Increasing the amount of nitrogen applied on slopes would increase the concentration of nitrogen loss, and the total amount of nitrogen loss would also increase by 6.00%~11.00%. The full amount of chicken manure instead of half the amount of urea would reduce the total nitrogen loss on the slope by 10.40%. When applying nitrogen fertilizer in agriculture, the application rate should be selected reasonably with the low rate and high frequency. Try to choose organic fertilizer instead of traditional nitrogen fertilizer to reduce the nitrogen concentration in surface runoff. The water and soil conservation should be done well to reduce the threat to the environment caused by the large amount of nitrogen in soil erosion.

Abstract:Accurate assessment of spatial distribution characteristics of soil erosion and nutrient loss is the basis of regional soil and water conservation and ecological environment governance. Based on GIS spatial analysis technology and RUSLE model, soil erosion and nutrient loss were quantitatively evaluated in Yunnan Province. The results showed that the soil erosion area was 1 835.91×10⁴ hm² in Yunnan Province, accounting for 48.07% of the total area, and the mean annual erosion modulus was 15.65 t/(hm²·a) with a total of 597.52×10⁶ t/a of potential soil loss. The intensity of soil erosion was mainly micro-erosion and mild erosion, but extremely strong erosion and severe erosion were the main sources of sediment yield. The soil erosion intensity was higher in southwestern Yunnan and lower in northwestern Yunnan. Soil erosion mainly occurred in summer (June-August), and dry land was the main source of sediment yield. The thickness of the lost soil layer was mainly distributed between 0 and 2 mm/a, and the average value was 1.19 mm/a. As the thickness of the lost soil layer increasing, the proportion of the corresponding area presented a decreasing trend. The average loss modulus of soil organic matter (SOM), total nitrogen (TN), available potassium (AK) and available phosphorus (AP) was 820.00 kg/(hm²·a), 55.19 kg/(hm²·a), 3.32 kg/(hm²·a), 0.32 kg/(hm²·a), respectively. The spatial distribution of the four nutrient losses had certain aggregation characteristics, and the overall performance was that the western region was larger than the eastern region. These findings could provide scientific basis for water and soil conservation planning and ecological environment construction in Yunnan Province.

Abstract:In order to explore the impact of different ecological restoration modes on the runoff and sediment production law of the dump in the opencast coal mine, according to the field runoff plot methods, the field standard runoff plot method was used to observe the runoff and sediment production of the dump in the mining area with different ecological restoration modes for a continuous rainy season. The results showed that: (1) The rainfall distribution in the study area is uneven during the year, mainly concentrated in the flood season from July to September, the rainfall in this period accounted for 77.03% of the average annual rainfall, which was the period with the largest loss of runoff and sediment in the year; (2) Compared with the bare slope (sowing only shrub and grass seeds), different ecological restoration modes had the effect of runoff and sediment reduction, but the benefits of different ecological restoration modes for runoff and sediment reduction were significantly different. Runoff reduction effect from large to small listed in the order of Salix psammophila checkerboard mode (64.35%) > Ecological rods mode (56.56%) > Ecological geo-textile bag mode (52.74%) > Wire gabion mode (48.70%) > Hedgerows mode (45.51%) > Soil improvement mode (35.89%) > Non-woven fabric covering mode (33.97%) > Gravel capping mode (8.19%);The sediment reduction effect were Salix psammophila checkerboard mode (69.41%) > Ecological rods mode (61.28%) > Ecological geo-textile bag mode (55.09%) > Wire gabion mode (52.43%) > Hedgerows mode (48.72%) > Soil improvement mode(42.09%) > Non-woven fabric covering mode (38.31%) > Gravel capping mode (19.34%); (3) The response characteristics of sediment yield from different ecological restoration modes were all significantly positively correlated (P<0.05, r>0), the Salix psammophila checker board mode had a smaller response to runoff, followed by the Ecological rods mode, and the Rock cover mode had the greatest response to runoff.

Abstract:In order to evaluate the effect of soil matrix improvement on soil erosion resistance during vegetation restoration of purple soil, relevant experiments were carried out in the purple soil area of Leiyang in south Hunan Province, China. Three soil matrix types were chosen in our study, including the untreated purple soil matrix (control land), the purple soil of interchanging topsoil with subsoil (soil replacement land), and the one added organic improver based on the soil replacement land (soil matrix improved land). Thirteen erosion resistance evaluation indexes were determined, the important indexes were screened out and an evaluation model was established to study the change of erosion resistance of purple soil substrate after soil matrix improvement, using the correlation analysis and the principal component analysis. The results showed that: (1) Compared with the control land, the organic carbon content, erosion resistant index, > 0.25 mm wet sieve aggregate content, > 0.5 mm wet sieve aggregate content, <0.002 mm clay percentage content, mean weight diameter of wet sieve aggregate, geometric mean diameter of wet sieve aggregate, structural granular index and aggregation condition in 0—10 and 10—20 cm soil layer increased by 69.19%~99.81%, 9.72%~46.86%, 41.69%~50.80%, 47.26%~58.98%, 73.82%~194.35%, 47.96%~57.01%, 49.06%~68.97%, 74.23%~183.25%, and 14.62%~20.16% in the soil matrix improved land, respectively. On the contrary, soil bulk density, fractal dimension of wet sieve aggregate and structural failure rate decreased by 10.53%~16.26%, 4.64%~7.58%, and 39.22%~54.64%, respectively. (2) Soil bulk density, organic carbon content and wet sieve aggregate content and stability were the main factors affecting the erosion resistance of purple soil. (3) Compared with the control land, the composite index of soil erosion resistance in 0—10 and 10—20 cm soil layer in the soil matrix improved land was significantly increased by 524.14% and 146.99%, respectively, and the one in the soil replacement land was increased by 93.10% and 42.17%, respectively. The results showed that the soil matrix improvement during vegetation restoration not only increased the organic carbon content of purple soil, but also significantly improved the soil erosion resistance, and this method can be used as an effective measure to control soil erosion in purple soil.

Abstract:To explore the effects of different treatment modes on soil erosion resistance in eroded degraded land of granite red soil, field investigation and laboratory experiment were conducted. Soil of five treatment modes in Changting county, including banned (M1), arbor-shrub-grass mixed forest (M2), whole slope grass sowing (M3), low efficiency forest transformation (M4) and the furrow grass shrub zone (M5), were taken as the research objects, clearage (CK1) and the bare land (CK2) were selected as the control. The main influencing factors of soil erosion resistance were revealed by principal component analysis, and the comprehensive evaluation of soil erosion resistance was carried out by combining grey correlation analysis and coupling analysis. The results showed that: (1) The order of soil erosion resistance under different treatment modes was M5 > M2 > M3 > M4 > M1 > CK2 > CK1. (2) The content of water-stable aggregate > 0.25 mm and organic matter content were the main factors affected soil erosion resistance. (3) The soil erosion resistance index was strongly correlated with the soil physical and chemical properties (0.696), and the coupling degree between soil erosion resistance and soil physical and chemical properties of M3 was the highest (0.883). The results provide a scientific basis for soil and water loss control and ecological restoration in eroded degraded land of granite red soil areas.

Abstract:The study on the change of vegetation coverage and its relationship with the driving factors is the basis of benefit evaluation on large-scale vegetation restoration, but the spatial-temporal change patterns of vegetation and its driving factors in the southwest karst trough-valley region are still not clear at present, which is not conducive to further ecological construction. This study explored the spatio-temporal characteristics and driving factors of vegetation coverage change based on the data of NDVI, air temperature, rainfall, DEM, land cover and population density in the southwest trough valley area from 2000 to 2018 and to predict the future trends. The methods of linear trend regression analysis and Hurst index analysis as well as the geographic detector model were applied. The results showed that: (1) In recent 19 years, the range of NDVI was 0.785~0.838, which showed a fluctuating upward trend, and the annual growth rate of vegetation NDVI (0.003 17/a) in karst area was significantly higher than that in non-karst area (0.002 60/a). (2) Hurst index analysis showed that the vegetation NDVI in the study area mainly showed an upward trend, but 64.31% of them would show a degradation trend in the future, and the situation of vegetation protection was more severe. (3) There was a negative correlation between NDVI and temperature change (R=-0.040) in karst area, but a positive correlation (R=0.013) in non-karst area. The results of residual analysis showed that human activities promoted the NDVI growth of 89.60% of regional vegetation. (4) In the whole karst trough-valley area, land cover type and air temperature were the main driving factors affecting NDVI, the interpretation rate was over 25%, and the interaction of each factor was obviously higher than that of a single factor. On the whole, human activities had a significant positive impact on the vegetation restoration in the southwest trough valley area.

Abstract:As the largest freshwater lake in China, revealing the spatial-temporal evolution of the rainfall erosivity and its impacts on sediment into the Poyang Lake is of great significance to scientifically guide the ecological protection and the development of the high-quality development of the ecological civilization in the basin. In this paper, change of the rainfall erosivity in Poyang Lake basin (PYLB) and its effects on suspended sediment load (SSL) into the lake were investigated based on the daily rainfall data of the 63 weather stations within the PLYB and the annual SSL into Poyang lake from its five tributaries from 1961 to 2017, using the non-parameter Mann-Kendall test, Double mass curve and Linear regression method. The results showed that annual average rainfall erosivity of PYLB was 10 034.1 (MJ·mm)/(hm²·h), ranging from 6 738.8 to 12 734.8 (MJ·mm)/(hm²·h). The spatial pattern of the rainfall erosivity showed that low rainfall erosivity mainly distribute in the southwest region and high rainfall erosivity mainly distribute in the northeast region. The rainfall erosivity showed an insignificant increasing trend (P>0.05) during 1961—2017, of which the greatest value was in the 2010s and the smallest in the 1960s. In the same period, the annual average total SSL into the lake was 1 183.3×10⁴ t, showing a significant decreasing trend (P<0.01). The greatest value of the SSL was in the 1970s and the smallest was in the 2000s.The change points of the total SSL into the lake and the SSL of the Ganjiang river, Xinjiang River and Shuishui River were in 1992, and 1999, respectively (P<0.01). Taken the period before the change points of the SSL as the baseline period, the contribution rate of human activity and rainfall erosivity on the total changes of SSL into the lake was -138.1% and 38.1%, respectively during the period after the change point. The contribution rate of human activity and rainfall erosivity on the SSL changes of the Ganjiang river was -125.8% and 25.8%, respectively. The contribution rate of human activity and rainfall erosivity on the SSL changes of the Xinjiang river was -121.3% and 21.3%, respectively. The contribution rate of human activity and rainfall erosivity on the SSL changes of the Xiushui river was -141.4% and 41.4%, respectively. The change of rainfall erosivity was advantageous to increase the SSL into the lake, and human activities, e.g. reservoir construction, soil and water conservation and sand mining were the main driving forces for the decrease of the SSL into the Poyang Lake in the recent 60 years.

Abstract:In order to analyze the properties of different soil types, and define the types of wind-erodible soil and explore their characteristics, the Yellow River Alluvial Area of Northeast Henan Province was taken as the research area. Field sampling and indoor experiment analysis were used to determine soil particle size, erodibility factor K value and other indicators, and then defined the types of wind-erodible soil in the area, and analyzed its spatial distribution feature. The main research results showed that: (1) In terms of soil types, there were four soil types in the Yellow River Alluvial Area of Northeast Henan, mainly fluvo-aquic soil, accounting for 65.57% of the area. In terms of subtypes, there were 11 soil subtypes. The main types were small zhejiang soil and sandy soil, accounting for 59.76% of the area. (2) In terms of the particle size composition of the soil, sandy soil, meadow aeolian sandy soil, salinized fluvo-aquic soil, and silt soil were dominated by sand. Other types were dominated by silt. Sandy soil, meadow aeolian sandy soil, irrigated fluvo-aquic soil, salinized fluvo-aquic soil had higher levels of erodible particles, with the range of 28.30%~31.36%. The K value of meadow alkaline soil, zhejiang soil and small zhejiang soil were relatively high, with the range of 0.038~0.041. (3) Comprehensively consider the two indicators of ‘the content of erodible particles ≥25%’ and ‘the erodibility is medium and above’, and the sandy soil, meadow windy sandy soil, irrigated and silted fluvo-aquic soil, salinized fluvo-aquic soil and degraded Fluvo-aquic soil were defined as regional wind-erodible soil. The wind-erodible soil area accounted for 41.79% of the study area, mainly in Zhongmou County, Xiangfu District, Weishi County and other regions. The results could provide reference and scientific basis for soil research and wind erosion control in the Yellow River Alluvial Area.

Abstract:Using the wind condition data and Google Earth satellite images, the wind condition characteristics and dune movement characteristics were analyzed in this paper. And the annual movement speed and direction and rules were studied, which was of great significance to the improvement of sand prevention and control means in the studied region. The results showed that: (1) The annual average wind speed in the study area was 1.535~1.768 m/s, the highest average wind speed of sand blowing occurred in May and June, while the lowest in January. (2) Sand blowing wind and sand transport potential were mainly distributed in the directions of WSW, W, WNW and NW. (3) The sand transport potential was between 0 and 26 VU, which was a low wind energy environment. The variability of wind direction was between 0.5 and 0.9, which belonged to the variability of stroke direction and blunt bimodal wind conditions. (4) The average annual moving speed of the dunes in the study area was 12.26 m/a, and the average forward movement of the dunes was above 10 m, which was the fastest type; the average moving direction was 125.13°, which was basically the same as the local synthetic sand transport direction. (5) Sand dune moving speed was negatively correlated with its height and width. In addition to height and width, wind speed, sand transport potential, and sand dune density also affected the moving speed of sand dunes.

Abstract:Based on remote sensing data and meteorological data, RWEQ model and wind erosion prediction model were used to evaluate soil wind erosion and analyze its driving factors in Inner Mongolia Autonomous Region from 2000 to 2017. The results showed that: (1) RWEQ model (R²=0.85, P<0.01) and wind erosion prediction model (R²=0.43, P<0.01) had a good correlation with ¹³⁷Cs tracer wind erosion, and RWEQ model had a better prediction accuracy. (2) In terms of time, the simulation results of RWEQ and wind erosion prediction model showed that the wind erosion in Inner Mongolia Autonomous Region showed a decreasing trend from 2000 to 2017, and the decreasing trend was 0.73 t/(hm²·a) and 1.18 t/(hm²·a), respectively. The wind erosion modulus of soil simulated by the two models reached the lowest value in 2011. Spatially, from 2000 to 2017, the simulation results of the two models showed that the soil wind erosion in Inner Mongolia Autonomous Region was dominated by slight and light erosion, and the severe erosion accounted for a relatively small proportion in the whole study area (RWEQ: 1.79%, wind erosion prediction model: 5.45%), which was mainly distributed in the southwest of the northern sandstorm area. The wind erosion modulus of 89.74% (RWEQ) and 72.05% (wind erosion prediction model) showed a decreasing trend, and the significantly decreasing areas were mainly distributed in the Badain Jaran Desert and Ulan Buhe Desert in the wind-swept area of northern China. (3) Wind erosion was significantly impacted by the windy days. With the increase of windy days, soil wind erosion showed a significant upward trend, and the increase of vegetation coverage and precipitation could inhibit the soil wind erosion to a certain extent.

Abstract:In order to explore the mechanism of rill erosion process on alpine soil slope in Southeast Tibet, establish the factor model of sediment transport capacity, and provide scientific basis for controlling soil and water loss on slope surface, this paper took the alpine soil in the Tibet Plateau as the research object, and carried out an indoor runoff scouring experiment. The results showed that: (1) The critical slope length of sediment transport capacity decreased with the increase of sediment transport capacity, ranging from 3.27 m to 8.31 m. When the slope was 15°~25°, the critical slope length was about 5.0 m. (2) Under different slopes, the sediment transport capacity increased with the increase of discharge, which could be well described by a linear equation (T_c=Aq). The influence of the same discharge on small slope was greater than that on large slope. (3) The sediment transport capacity and slope could be well expressed by an exponential equation (T_c=-ae^(-S/b)+c). With the increase of slope, the sediment transport capacity increased rapidly at first, and then gradually leveled off, and increased gently when the slope reached 15°. (4) The sediment transport capacity could be expressed by a two-dimensional power function equation T_c=1697.83S^0.491q^1.043. Compared with other models, ANSWERS model was not suitable for calculating sediment transport capacity of Alpine soil, but the performance of Zhang model, Gao model and Lei model were as good as this model.

Abstract:In order to systematically study the mechanical effect of shrub roots on soil consolidation and explore the friction characteristics of soil to roots, taking four different soil particle sizes (<2.0, 1.0~2.0, 0.5~1.0 and <0.5 mm) and three-year-old typical slope protection plants, Pyracantha fortuneana and Amorpha fruticosa, as the research objects, the direct shear friction test of root soil interface was carried out in laboratory. The results showed that: (1) The friction strengths of root-soil and soil-soil interface were positively related to the vertical load. With the increasing of soil particle size, the friction strengths, friction coefficients, cohesions and friction angles of root-soil and soil-soil interface all decreased, and within the same particle size range, the friction characteristics of P. fortuneana root soil interface were significantly better than those of A. fruticosa and plain soil. (2) The shear stress of the root soil interface and the plain soil interface increased first and then decreased with the increasing of displacement. The relationship curve of root soil interface shear stress and displacement showed a zigzag rise, while the plain soil curve showed a gentle rise. (3) The smaller the soil particle size was, the larger the specific surface area of the indirect contact surface between the root and soil was. The small soil particles inlayed with the root surface, which increased the bite force of the contact surface and increased the friction capacity. The above research had a certain theoretical significance for further exploring the mechanical mechanism of root soil interaction of shrub plants, and improving the stability of slope soil in the experimental area by use shrub plants and preventing the shallow sliding of slope.

Abstract:To clarify the non-linear influence mechanism of landscape feature on the sediment yield during the "Grain for Green" project, our study selected 33 hydrological station-controlled sub-basins in the in Hekouzhen Longmen Section of the middle reaches of Yellow River during 2006—2016. We used the boosting regression tree method to analyze the non-linear relationships between landscape drivers and sediment yield modulus of the selected sub-basin. The results showed that the proportion of forest and agricultural land contributed the most to the variation of the sediment yield modulus, which contributing 22.0% and 16.9% respectively. Increasing the proportion of forest land or decreasing the proportion of agricultural land can reduce the sediment yield modulus, but when the proportion of forest land area exceeds 15% or the agricultural land area is less than 20%, the increasing rate of sediment yield modulus becomes stable. Increasing the vegetation coverage of forest land and grass land also has a threshold for mitigating soil erosion, and the threshold value of normalized difference vegetation index (NDVI) in grass land and forest land is 0.5 and 0.3 respectively. When the NDVI value below the threshold, the sediment yield modulus decreases rapidly with increase in NDVI, but the effect of vegetation improvement in grass land and forest land on sediment yield modulus is stable when exceeded the thresholds. Reducing the number of edge density (ED) appropriately is conducive to controlling soil erosion, when the ED maintained at 60/100 hectares can achieve the prevention and control of soil erosion effect. The research reveals the non-linear relationships between landscape characteristics and sediment yield at watershed scale, which can provide an important reference for the reasonable vegetation restoration in the Yellow River.

Abstract:In view of the weak research on the unbalanced sediment transport characteristics of rainfall-runoff erosion under the combined action of rainfall and bed roughness, the variation characteristics of rainfall-runoff sediment transport under different rainfall intensities and slope lengths were studied by using the indoor simulated rainfall test. The results showed that: (1) Under the condition that the slope was a bare slope and the slope was 10°, when the slope length increased from 1 m to 8 m, the sediment concentrations of runoff increased by 3.28~7.15 times under the same rainfall intensity. The runoff sediment concentrations increased with the increase of rainfall intensities. When the rainfall intensities increased from 40 mm/h to 120 mm/h, the runoff sediment concentrations increased by 1.41~2.97 times under the same slope length. (2) According to the existing formula of sediment carrying capacity of river channel, after analyzing the influence of rainfall, slope, slope length and other factors on runoff sediment carrying capacity, and based on the rainfall test data and collected test data, the formula of sediment carrying capacity under rainfall condition was obtained, which could be applied to the calculation of sediment carrying capacity of overland flow under rainfall condition. (3) The influence of rainfall intensity on restoring saturation coefficient was discussed, and the unbalanced sediment transport model was proposed and verified. The verification results showed that the model had a good simulation effect on the variation of rainfall runoff sediment concentration along the slope. These results could provide reference for predicting the variation of sediment concentrations along the slope runoff and improving the erosion mechanism of thin layer runoff.

Abstract:Dongjiang River Basin was selected as the study area, which is located in the south of Jiangxi Province, China. The SWAT model was used to evaluate the influence of different watershed delineation on runoff and sediment yield. Eleven scenarios including the sub-watershed thresholds were 25, 50, 100, 200, 400, 800, 1 100, 1 500, 2 000, 3 200, 4 000 hm², were used to analyze the impact of soil spatial discretization on runoff and sediment yield. Terrain and land use data were input a single terrain and soil data to fix the effect of terrain and soil data spatial discretization. The results were as follow: (1) The discretization effects of soil parameter significantly increased with the increasing of sub-watershed, the largest area of latosol reduced significantly (P<0.05), the second largest area of osmotic paddy soil and the third largest area of yellow soils increased significantly (P<0.05). Lithosol soil, the smallest area soil type, was totally disappeared by soil discretization when the number of sub-watershed was under 267, while it increased when the number of sub-watershed was more than 524 (P<0.05). (2) The spatial discretization of soil parameters reduced the annual runoff (1.32%, P<0.05) and annual sediment yield (18.07%, P<0.05), and the sediment yield decreased greater than annual runoff. (3) The annual maximum one-day, annual maximum five-day, and annual maximum seven-day sediment yield decreased significantly with the increase of delineation degree (16.64%, 17.54%, 17.34%, P<0.01), while the sub-watershed delineation had less influence on the annual maximum one-day, annual maximum five-day and annual maximum seven-day runoff yield (0.59%, 0.89%, 0.83% P>0.05); (4) The peak sediment yield decreased significantly with the increase of delineation degree, while the effect for peak runoff was not significant. The soil parameters spatial discretization of watershed subdivision mainly affected the change of sediment yield through the change of K-factor. The research results will provide reference information for the selection of optimal computing units, improving the simulation accuracy and reducing the uncertainty of model simulation.

Abstract:In order to explore the effects of human activities and climate changes on the runoff and sediment yield in the Yellow River, a typical watershed in the middle reaches of the Yellow River——Xinshui River watershed, was selected as the research area to analyze the annual variation of hydrometeorological factors from 1958 to 2015. The Mann-Kendall test and Pettitt test were used to analyze the trend and mutation of runoff, sediment discharge and sediment concentration. In addition, double cumulative curve method, regression analysis method and elastic coefficient method were used to evaluate the attribution of runoff and sediment yield. Results show that: (1) The annual average runoff, sediment discharge and sediment concentration were 32.0 mm, 1 289.1 t/km² and 33.7 kg/m³, respectively. They all exhibited a significant decreasing trend on the annual scale. The results of mutation test showed that the abrupt change in annual runoff, sediment discharge and sediment concentration all occurred in 1980. (2) Before 2002, the relationship between annual runoff and sediment yield showed a good linear relationship. However, the correlation between annual runoff and sediment yield was significantly weakened during 2003—2015, which was difficult to be represented by a definite regression equation. The main reason was that the implementation of soil and water conservation engineering measures, especially the construction of check-dam, weakened the runoff-sediment relationship. (3) The results of double cumulative curve method, regression analysis method and elastic coefficient method were relatively close. Human activities were the main driving factors of runoff and sediment variations in the Xinshui River watershed. The traditional empirical statistical method does have certain reliability and applicability. This study can provide scientific basis for ecological restoration and regulation of runoff and sediment in the Yellow River watershed.

Abstract:Timely understanding and quantitatively analyzing the change trend of natural ecosystem and its response to ecological water transport process in arid and semi-arid areas is great significance to maintain the health of oasis ecosystem. Combined with remote sensing images and ecological water transfer monitoring data, this paper studied the temporal and spatial evolution characteristics of the Eichmann Lake wetland of Aksu River basin and its response to ecological water transfer. The results showed that the water area of Eichmann Lake shrunk seriously, from 61.57 km² in 1996 to 27.76 km² in 2020. The changes of water area experienced three stages, including rapid decline, slow decline and slow recovery. Water area of Eichmann Lake showed obvious seasonal change and lag effect after ecological water transfer, and the peak value appeared around November. Ecological water transfer had a significant lifting effect on the groundwater level, and was affected by water conveyance volume and water conveyance days. There was an obvious lag effect between the change of groundwater level and ecological water transfer, which was 1~2 months. The response characteristics of different natural vegetation to ecological water transfer were different. The response of Populus euphratica to ecological water transfer was more obvious. The growth of P. euphratica was the best in the range of 100~500 meters from the water delivery outlet. The monthly variation of NDVI showed that the lag time of ecological water conveyance on natural vegetation growth was about one month. This research could provide valuable reference fornatural restoration, regional water resources allocation and ecological water demand regulation in Aksu River Basin.

Abstract:Plastic mulching (PM) technology can effectively improve the crop productivity in the dryland. However, few studies have been conducted to determine PM effect in different soil moisture conditions before sowing. Based on the winter wheat-summer maize rotation experiment with PM from 2013—2016, the Aquacrop model was tested, and then different levels of soil moisture before sowing were set up in Baoji, Wugong, and Xi’an using the historical climatic data. The response law of the plant growth and water use during summer maize growing seasons to soil moisture before sowing was explored under PM, and the criterion for using PM was established. Results showed that when the initial soil water content before sowing (ISWC) was less than 70% of field capacity (FC), the maize yield greatly fluctuated in the three sites. The yield increment for both non-mulching and PM treatments increased with the precipitation. With the increasing ISWC, the increment in yield became more and more obvious, which was less and less sensitive to precipitation, and finally tended to be stable under PM. When ISWC reached 80%~85% of FC, the maize water use efficiency under PM reached the highest level. To sum up, the soil water availability was one of the prerequisites for the yield promotion effect under PM. When the ISWC is less than 70% of FC, PM is not recommended; when the ISWC is greater than 80% of FC, PM is recommended to farmers.

Abstract:Forest soil is the basis for the survival and restoration of forest vegetation. Disturbance not only affects the dynamic changes of forest soil organism sand abiotic, but also has an important impact on the structure and function of forest ecosystem. The study selected three types of disturbance (clearing litter, resin tapping and fire) Pinus massoniana forests in central Guizhou as the research object, and set up undisturbed P. massoniana forest plots around each of the disturbance plots as the control, to reveal the influence characteristics of different disturbance types on soil properties of P. massoniana forest. The results showed that there were significant differences in the soil properties of the P. massoniana forest among different soil layers (P<0.05), and the nutrient content of the top soil (0—20 cm) was significantly higher than that of the lower soil (20—40 cm and 40—60 cm), which indicated that the soil nutrients of the P. massoniana forest had "surface accumulation" effect. Different disturbance types had a significant impact on the soil properties of the P. massoniana forest (P<0.05). Under the disturbance of resin tapping, soil nutrient content and urease activity increased, and there was no significant difference in contents of total phosphorus and available phosphorus. Under the disturbance of litter removal, the soil pH, organic carbon content, total nitrogen content and urease activity of the P. massoniana forest decreased, and there was no significant difference in the bulk density, total phosphorus content, available nitrogen content and available phosphorus content, while the available potassium content and catalase activity increased. Under fire interference, the bulk density, available potassium content and catalase activity of the P. massoniana forest increased, while the contents of organic carbon, total nitrogen, total phosphorus and available nitrogen, as well as urease activity showed a downward trend, while the contents of organic carbon and available phosphorus did not unchanged significantly. Under different interference types, there was a significant correlation between soil enzyme activity and chemical properties. The significant correlation in surface soil was greater than that in deep soil. Urease activity was significantly correlated with contents of total nitrogen and available nitrogen, and catalase activity was significantly correlated with organic carbon content. Under different interference types, there were certain differences in soil nutrient variability. The soil pH was weak variability, and most of the remaining soil nutrients were medium variability. In summary, different types of disturbance had a great impact on the soil properties of the P. massoniana forest. Sufficient attention should be paid to the utilization and protection of the P. massoniana forest in this area, and rational management and utilization should be given.

Abstract:In order to explore the restoration of forest resources after the implementation of forestry ecological projects such as Grain for Green Project in the residual gully region of the Loess Plateau, the calculation was based on the DEM data of the Loess Plateau and the normalized vegetation index NDVI data from 2000 to 2020. The calculation of topographic factors, hydrological analysis, spatial overlay analysis, etc, were used to divide the relatively complete range of the residual gully region of the Loess Plateau area. The trend analysis and coefficient of variation were used to analyze the characteristics of the temporal and spatial changes of NDVI in the residual gully region of the Loess Plateau area. The results showed that: (1) The residual gully region of the Loess Plateau area spanned three provinces of Shanxi, Shaanxi, and Gansu, covering an area of approximate 29 900 km², and the gully density was between 1.91~3.21 km/km². (2) The NDVI of residual gully region of the Loess Plateau area varied with time, the total average NDVI value of the region for 21 years was 0.711, and the change trend of vegetation NDVI in this area from 2000 to 2020 showed a fast-slow-fast growth. In terms of spatial distribution, the vegetation coverage was generally in the range of NDVI value 0.6~0.9. The vegetation coverage in the central part of the study area was higher than those of other areas in the study area. (3) In terms of temporal and spatial trend characteristics, the vegetation coverage in the western and eastern parts of the study area had improved significantly, and the vegetation coverage in the central area of the study area was relatively stable. In terms of temporal and spatial fluctuation characteristics, the vegetation NDVI in this area fluctuated steadily in time series, and the difference in spatial fluctuation was large, and the area of low fluctuation area accounted for 48.06%. On the whole, the residual gully region on the Loess Plateau was mainly distributed in three provinces: Shanxi, Shaanxi and Gansu. From 2000 to 2020, the NDVI of vegetation in this area showed an overall upward trend. The overall vegetation coverage level was relatively high with low fluctuations, and showed a trend of improvement. These results could provide theoretical and scientific basis for soil and water conservation in the residual gully region on the Loess Plateau.

Abstract:In order to explore the effective biological measures suitable for the control of rocky desertification in karst area of Southwest China, the Dabang River, a typical karst basin, was taken as the research area. Using the SWAT model simulation method, the long-term measured hydrological data from the Huangguoshu and Gaoche hydrological stations were used for calibration. Totally six scenarios of rocky desertification control measures were set up to simulate the runoff generation characteristics. And finally, the ecological benefits of different measures were discussed. The results showed that: (1) In the calibration period (2008—2013), as for Huangguoshu hydrological station, R²=0.86, NSE=0.77, while for Gaoche hydrological station, R²=0.76, NSE=0.63; and during the verification period (2014—2018), the R² of Huangguoshu hydrological station was 0.79, NSE was 0.57, while the R² of Gaoche hydrological station was 0.75, NSE was 0.54, which all met the evaluation criteria of the model, indicating that SWAT model had good applicability in Dabang River Basin. (2) When the slope was greater than 15°, the effects of water storage and interception of woodland, economic forest and grass land were better than that of farmland. When the slope was between 15° and 25°, and above 25°, the effects of water storage and interception were: economic forest > grassland > woodland. (3) On the one hand, the economic forest + grassland measure could effectively alleviate the problem of engineering water shortage in Dabang River Basin; on the other hand, based on the potential economic benefits, optimizing and adjusting the planting structure of local farmland could realize the sustainable development of regional agriculture. These results could provide theoretical reference for rocky desertification control, ecological restoration and Rural Revitalization in southwest karst area, and have certain reference significance for promoting social and economic sustainable development of karst basin.

Abstract:Soil erosion-deposition is one of the essential mechanisms affecting the geochemical cycle of terrestrial ecosystem. In this study, the spatial distribution characteristics of soil biological, chemical and physical properties in erosion sites and deposition sites were systematically analyzed. The erosion-deposition plots were constructed based on the erosion-deposition geomorphic characteristics of the China’s Loess Plateau, including erosion sites with three slope gradients of 5°, 10° and 20°, and each erosion site was connected with a deposition site. During the experimental period (2015—2019), continuous in-situ monitoring of runoff, sediment, soil temperature and moisture under natural rainfall conditions were conducted. Soil samples were regularly collected for analyzing the physical and biochemical properties. The results showed that: (1) With the increasing of slope gradients, the intensity of soil erosion increased. In specific, compared with 5° slope, the annual runoff on 10 ° and 20 ° slopes increased by 30%~115% and 48%~207%, respectively, meanwhile, the annual sediment yield on the 10° and 20° slopes increased by 146%~505% and 241%~742%, respectively. (2) The concentrations of soil organic carbon, dissolved organic carbon, mineral nitrogen, soil microbial biomass carbon and nitrogen and the clay content in the deposition sites were all significantly higher than those in erosion sites. However, the relative abundance of δ¹³C was 2.0%~3.3% higher in the erosion sites than that in the deposition sites. (3) The difference of soil properties between erosion site and deposition site increased with the increasing of slope gradients. Our results suggested that soil physical and chemical properties had opposite responses to soil erosion and deposition.

Abstract:In order to study the effects of different irrigation quotas on the growth of red jujube and the dynamic changes of soil moisture under drip irrigation in the Hetian area of southern Xinjiang, four moisture gradients were designed to study the changes of new shoots, photosynthesis and yield under different water gradients, and the soil water content in the whole growth period of jujube was measured by drying method. Jujube trees grew faster at the budding leaf development stage and the flowering and fruit-setting stage. The length and diameter of the jujube new shoots followed the order of W33/667 m²) treatment was more suitable for drip irrigation red jujub growth, with the highest yield (540.56 kg/667 m²) and the highest irrigation water use efficiency (1.29 kg/m³).

Abstract:The development of crack reduces soil bearing capacity, shear strength, cohesion and other mechanical properties, promotes wall collapse. Under the condition of controlling soil thickness (0.8 cm, 1.6 cm and 2.2 cm), the indoor dehumidification test was carried out on the four layers of Benggang soil. The crack evolution characteristics of Benggang soil were analyzed by taking photos at fixed time and fixed points with a camera sand combined with digital image processing technology. The results showed that: (1) During the dehumidification process, the soil deformation first produced radial shrinkage and then the cracks developed, and the transition layer of four layers soil first produced radial shrinkage and cracks. (2) Among the four layers of soil, the degree of crack development followed the order of transition layer > laterite layer > topsoil layer > sandy layer. The large difference between transition layer and sandy layer would destroy the stability of Benggang soil and accelerate wall collapse. (3) With the increasing of soil thickness, crack development gradually weakened, and the core shrinkage phenomenon increased gradually. For the Benggang soil with a diameter of 12 cm, when the thickness was 2.2 cm, there was no crack development and only core shrinkage. The research results could provide scientific bases for studying the collapse mechanism and improving the stability of Benggang soil.

Abstract:The soil infiltration test was carried out under the main forest types (Robinia pseudoacacia Linn., Pinus tabulaeformis Carr., Robinia pseudoacacia×Pinus tabulaeformis mixed forest, and Populus davidiana and Pinus communis natural secondary forest) in the gully region of the Loess Plateau by the double-ring infiltration method, and the soils were analyzed for physical and chemical characteristics to analyze their influence on the process of soil infiltration. The results showed that: (1) There were certain differences in soil physical and chemical characteristics of different forest types in the study area, and the soil physical and chemical properties of the natural secondary forest of Populus davidiana and Pinus communis were generally the best. The mixed forest of Robinia pseudoacacia×Pinus tabulaeformis was better than that of Robinia pseudoacacia Linn. and Pinus tabulaeformis Carr.; (2) Within the test period of 0~90 min, the soil infiltration rate of different forest types showed a rapid decrease (0~5 min) and a gradual decrease (5~60 min) over time, and the process of stabilization (60~90 min); the initial soil infiltration rate, stable infiltration rate and average infiltration rate of the four forests in descending order were as follows: Populus davidiana and Pinus communis natural secondary forests, Robinia pseudoacacia×Pinus tabulaeformis mixed forest, Robinia pseudoacacia Linn., and Pinus tabulaeformis Carr.; (3) Among the four common soil infiltration models (Kostiakov model, Horton model, Philip model and general empirical model), the general empirical model had the best fit for the soil infiltration process under different forest types in the study area, the fitting accuracy was above 0.990; (4) Correlation analysis results showed that the soil infiltration indices under different forest types were significantly negatively correlated with soil bulk density (P<0.01), and were positively related to non-capillary porosity, > 0.25 mm water-stable aggregate content, sand content and the organic matter content (P<0.01); through path analysis and calculation of the determination coefficient of the main influencing factors, the results showed that the factor that had the greatest influence on the initial soil infiltration rate was the soil bulk density (0.309). The factor that had the greatest influence on the stable soil infiltration rate was > 0.25 mm water-stable aggregate content (0.251), and the factor that had the greatest influence on the average soil infiltration rate was organic matter (0.408). These research results could provide a certain reference for the selection of tree species and the evaluation of soil and water conservation functions in the study area to build soil and water conservation forests.

Abstract:Soil water content in artificial Pinus tabulaeformis forestland, native grassland and farmland in the loess region of western Shanxi province were observe and studied to define the effects of different land use types on soil moisture. The water content in 0—10 m soil layer was measured by soil core method from April to October in 2019 and 2020. The results showed that: (1) The soil water storage of the 0—10 m soil profile in artificial P. tabulaeformis forestland was 1 281.13 mm, 1 712.85 mm in native grassland, and 1 804.77 mm in farmland. P. tabulaeformis forest land consumed 431.72 mm and 523.64 mm water more than wasteland and agricultural land, respectively, and the more consumed soil water mainly came from deep soil. (2) The vertical change of water content in 0—10 m soil layer of three land use types could be divided vertically into three layers, including severe-changing layer, weak changing layer and relatively stable layer, and the change of water content in each layer with time was also different. (3) The depth of root water absorption was 5.4 m for P. tabulaeformis, 4.2 m for crops. The influence of depth was 10 m for P. tabulaeformis, 8 m for crops. Crops could be planted on flat and accessible sites in the study area to promote the local agricultural economy. In view of the low soil water content in P. tabulaeformis forest land, appropriate water management measures could be used to reduce stand water depletion in P. tabulaeformis forestland.

Abstract:Vegetation restoration and reconstruction in arid and semi-arid areas are highly dependent on precipitation, and any slight change in precipitation pattern will have an impact on its ecosystem. Taking three main cover types of desert steppe in Yanchi County of Ningxia, floating sand land, native grassland and Caragana woodland as research objects, the precipitation and soil moisture from 2015 to 2017 were continuously observed by automatic weather station and soil moisture meter, the soil moisture dynamics of 0—250 cm soil layer and the responses to different levels of precipitation were analyzed. The results showed that the soil moisture of floating sand land increased from the surface to the deep layers, and the native grassland and Caragana woodland had the increasing-decreasing-increasing trends; seasonal changes in water content were divided into stable soil moisture period (December to February of the following year), soil moisture accumulation period (March to May), soil moisture decay period (June to mid-August) and soil moisture recovery period (late August to November). Small precipitation events less than 5 mm had almost no effect on soil moisture; moderate precipitation events (5~25 mm) and heavy precipitation events (25~40 mm) could supplement soil moisture in 0—20 cm soil layer or 0—40 cm soil layer in floating sand land. Extra-large precipitation event was needed for the water supplement of 40—100 cm soil layer. Floating sand land was the most sensitive to precipitation, followed by Caragana woodland, and native grassland was the most lagging. Precipitation amount, precipitation intensity, soil water content before precipitation and soil physical properties all affected soil water infiltration. When precipitation was consistent, soil type was the important factor determining soil moisture dynamics. Vegetation could redistribute soil profile moisture, which is particularly important in arid region ecosystem, and determines the corresponding relationship between vegetation types and soil types.

Abstract:To test the appropriate proportion of slow-release nitrogen (N) to the total N application in the one-time application strategy for single-cropping rice, to provide theoretical guidance for efficient fertilization of single-cropping late rice, a field experiment was carried out in Heping Town, Changxing County, Zhejiang Province from 2019 to 2020. The experiment consisted of six treatments: (1) No N fertilizer (N0); (2) Conventional fertilization (U1, base fertilizer∶tillering fertilizer∶panicle fertilizer=4∶3∶3); (3) Reduction conventional N rate by 12.5% (U2, the proportion was the same as U1); (4) 57% slow-release N with one-time application (SRU1); (5) 45% slow-release N with one-time application (SRU2); (6) 34% slow-release N with one-time application (SRU3). The N application rate was 240 kg/hm² for U1, and 210 kg/hm² for U2 and SRU. The rice yield, nutrient uptake, nutrient utilization efficiency, ammonium N content in-field water, and ammonia volatilization were measured. The results showed that the yield of single cropping rice in N0 was 73.55% of that in U. Compared with U, one-time application of slow-release N fertilizer could maintain rice yield. The yield of single cropping rice tended to increase with the increase of the proportion of slow-release N application. There was no significant difference in aboveground N content and N uptake between SRU and U. Compared with U, the N use efficiency of SRU2 in 2019 and SRU1 in 2020 increased by 10.49% and 8.84% respectively, reaching the significant difference level, but there was no significant difference between other treatments and U1 and U2. Compared with U, SRU significantly reduced the content of ammonium N and cumulative ammonia volatilization in-field water, but there was no significant difference among slow-release fertilizers. According to the results of related yield and N loss, one-time application of 34% slow-release N application ratio could meet the nutrients requirements of single cropping rice, ensure stable rice yield and reduce N runoff and volatilization loss at the same time.

Abstract:Farmland soil organic carbon pool is one of the most important soil carbon pools in terrestrial ecosystem. Clarifying the spatial distribution characteristics and influence mechanism of farmland soil organic carbon can provide sampling and theoretical basis for the evaluation of soil fertility and carbon sequestration capacity. Taking a typical agricultural irrigation and drainage unit (area: 45 hm²) in the Jianghan plain as the research object, the soil organic carbon contents (SOC) of 1 560 soil samples in 104 sites with the depth of 0—200 cm were measured, and the soil carbon density (SOCD) was calculated. We revealed the spatial characteristics and the distribution patterns of soil organic carbon density, and analyzed the influence of cultivation mode and history on its distribution. The results showed that: (1) In the 0—200 cm soil profile, the mean variation of SOCD in the 20 cm and 200 cm soil layer was 1.75~3.77 kg/m² and 11.67~34.24 kg/m², and the SOCD decreased sharply at first and then increased slowly as the increase of soil depth. The SOCD in 100—200 cm soil layer accounted for about 45.26% of the whole soil profile. Therefore, we should pay more attention to the deep-layer SOCD. (2) The SOCD in 0—20 cm and 0—200 cm soil layer under an Irrigation-Drainage Unit had strong spatial autocorrelation, indicating that structural factors such as soil parent material and topography were the dominant factors affecting the spatial distribution of SOCD under an Irrigation-Drainage Unit. (3) The SOCD among different cultivation modes and history were significantly different. It showed that the SOCD of all soil layers in paddy field was higher than that of upland field. The SOCD of was1.31 times that of upland field in the 0—200 cm, and the old paddy field was higher than the new paddy field in all soil layers. However, the difference between the total SCOD of the woodland to paddy field and the SCOD of the dryland to paddy field was relatively small in the 0—200 cm, while the higher SOCD was observed in woodland than dryland. The above shows that increasing the area of paddy field is one of the effective ways to rapidly increase farmland carbon storage. (4) The representative stable depth of SOCD at the scale of irrigation and drainage units was 180—200 cm, and the sampling depth should be extended as deep as possible when we investigated SOCD. These results provide a scientific basis for improving the accuracy of estimation of SOCD and the rationality of sampling design, as well as the evaluation of soil carbon sequestration capacity.

Abstract:Inorder to explore the influence of different particle gradations in muddy water on the infiltration law and formation characteristics of tight layer, indoor vertical infiltration experiments of soil pillars were conducted. In this study, four types of sediment with different physical clay content (5.59%, 9.87%, 18.43% and 39.43%) were selected and the variation characteristics of the thickness of the falling silt layer, the wet front migration distance and the cumulative infiltration volume with the infiltration time were studied, and the gradation of soil particles in the falling silt layer and the different depths after the infiltration (0—1 cm, 1—2 cm) were measured. The results showed that the greater the content of physical clay in the muddy cement sand was, the greater the thickness of the falling silt layer was. At the same infiltration time, the migration distance of the wet front and the cumulativ e infiltration amount per unit area decreased with the increasing of the physical clay content. The variation of the falling silt layer thickness with time conformed to the power function relationship (R² > 0.9), and the fitting coefficient decreased with the increasing of the physical clay content, and the fitting parameter changed around 0.5. Under different physical clay contents, the particle composition of the silt layer was similar to that of infiltration sediment. The particle composition of soil at 2 cm infiltration depth was similar to that of the original soil. The content of fine particles <2 mm in the soil at 1 cm infiltration depth increased compared with the original soil. With the increasing of physical clay content, the contents of fine particles <2 mm increased by 4.29%, 4.92%, 7.96% and 16.30% in different treatments, respectively. The research results could provide a theoretical basis for further exploring the characteristics of dense layers formed by muddy water infiltration.

Abstract:Vegetation cover and its pattern generally determine the mechanisms in the runoff and sediment reduction under different flow rates. In this paper, the responses of sediment yield to the interaction effects of vegetation cover age and slope positions were revealed through field experiments, including the lowest coverage pattern, relatively concentrated distribution on the upper of the slope, relatively concentrated distribution on the middle of the slope, relatively concentrated distribution on the lower of the slope, and the highest coverage pattern. Then the relation between hydrodynamic connectivity of slope and soil erosion were analyzed by three kinds of hydrological connectivity indexes (FL, FL_r, FL_s). The results showed that: (1) Vegetation cover and its pattern are important factors affecting slope soil erosion process. The sediment yield of the slope with vegetation coverage of 13.5% was about 2.36 and 3.02 times of the slope with coverage of 34.0%, respectively. At the same time, compared with relatively concentrated distribution on the upper and middle of the slope, relatively concentrated distribution on the lower of the slope was mostly in the slope. The regulation functions on runoff and sediment with the grass strip relatively concentrated distribution on the lower part of the slope were generally worse. Among them, the runoff amount increased by 16.42% and 8.00%, respectively, and the sediment yield increased by 26.53% and 23.56%, respectively. However, with the increase of the flow rates, the gap between the yields of runoff and sediment in different vegetation coverage was reduced. (2) FL, FL_r and FL_s, the important indexes of hydrological connectivity, exhibited linear correlation relationship to vegetation coverage. Meanwhile at the condition of three kinds of grass strip positions, the difference of FL was obvious. Under the experimental conditions, compared with the relatively concentrated distribution on the middle and lower of the slope above, the FL on the relatively concentrated distribution on the upper slope were decreased by 10.89% and 18.33%, respectively. By the research, there was no significant covariability has been found between the FL_r and FL_s with vegetation patterns. But it could flexibly reflect the changes in hydrological connectivity under different test conditions. (3) There were significant correlations between the hydrological parameters and slope soil erosion. And the increase of FL_r and FL_s and the decrease of FL could cause an exponentially reduction in the amount of runoff yield and sediment production. Thus, FL, FL_r, and FL_s can be used to indicate the hydrodynamic parameters of slope surface water flow and sediment yield in the change. The results have reference value for deep understanding of slope erosion process and quantitative evaluation of hydrological connectivity and vegetation and slope erosion, providing evaluation of random erosion prediction model and regional ecological environment construction.

Abstract:The effects of different water and fertilizer combinations on the photosynthesis, yield, water and fertilizer use efficiency and quality of broccoli under drip irrigation were studied. The regression model and principal component comprehensive evaluation system of yield quality and water and fertilizer factors of broccoli were established to seek the optimal combination of irrigation amount and fertilizer amount, so as to provide technical basis for improving the quality and efficiency of efficient water-saving irrigation of broccoli. Taking broccoli as the experimental crop, drip irrigation under mulch was adopted, and two factors and three levels randomized block experiment design was adopted. The irrigation amount was set at three levels, which were 1 740, 2 175, 2 610 m³/hm², and the fertilization amount were 1 200, 1 500, 1 800 kg/hm². There were nine treatments. The results showed that in the growth period, the precipitation was 20.8 mm, the irrigation amount was 2 610 m³/hm², and the fertilization amount was 1 800 kg/hm². The yield and quality of broccoli were the best, 2 610 m³/hm² irrigation and 1 800 kg/hm² fertilization, and the comprehensive evaluation score was also the highest, which indicated that the high water and high fertilizer treatment was the most favorable for the growth of broccoli, and it was a suitable irrigation and fertilization strategy for local drip irrigation of broccoli.

Abstract:Species diversity and functional diversity are the hot issues in ecology. The research on the relationship between them is the key to understand the function and process of community ecosystem. Based on variance analysis and principal component analysis, the relationship between plant species diversity and functional diversity was studied by using the function fitting analysis. The results showed that: (1) The vegetation functional diversity of limestone soil increased significantly (P<0.05) compared with the free grazing conditions. With the increase of the enclosure period, species diversity decreased significantly (P<0.05). The functional diversity did not change significantly (P>0.05). The plant functional diversity and species diversity in the aeolian soil area did not change significantly (P>0.05). (2) The relationship between functional diversity and species richness could be described by a quadratic polynomial Y=aX²+bX+c. With the increase of the enclosure period, the correlation coefficient of the two factors increased in both habitats of limestone soil and aeolian soil. In conclusion, the species diversity was positively correlated with the functional diversity in desert steppe, showing aquadratic function relationship. The species diversity could be used to reflect the level of functional diversity of plant community, but the replacement effect was affected by the period of enclosure and grazing. With the increase of the enclosure period, the ability of species diversity to reflect functional diversity level increased. In the future, the multi-dimensional characteristics of diversity and different soil habitat types should be considered to maintain the relationship mechanism between diversity and ecosystem function.

Abstract:The soluble nitrogen component of soil is the most active part of the nitrogen cycle, and it is the key link between "plants-soil nitrogen components-soil nutrients". Therefore, in order to explore the effects of vegetation types on the accumulation and availability of soil nitrogen in the loess hilly and gully region, this paper took four typical vegetations (barren grassland, Hippophae rhamnoides, Xanthoceras sorbifolium, Picea asperata) as the research objects. We analyzed the difference of soluble organic nitrogen (SON), ammonium nitrogen (NH₄⁺—N), nitrate nitrogen (NO₃^-—N) contents, density and the proportion of TN in the 0—10, 10—20, 20—40 cm soil layers. The results showed that compared with the barren grassland, the SON content in the 0—40 cm soil layer showed the highest performance in Picea asperata (19.0%), and the SON contents under Xanthoceras sorbifolium and Hippophae rhamnoides were decreased by 7.0% and 13.2% respectively. The NO₃^-—N content was the highest under Hippophae rhamnoides (20.9%), and the contents under Xanthoceras sorbifolium and Picea asperata were decreased by 5.0% and 48.0% respectively. Compared with barren grassland, the NH₄⁺—N contents under three vegetations were decreased by 19.0%~29.1%. Similarly, the SON density of Picea asperata was increased by 31.17%, and the values under Hippophae rhamnoides and Xanthoceras sorbifolium were decreased by 12.8% and 4.3% respectively. The NO₃^-—N density of Hippophae rhamnoides was increased by 21.4%, and the NO₃^-—N densities under Xanthoceras sorbifolium and Picea asperata were decreased by 3.5% and 42.6% respectively. The NH₄⁺—N densities of the other vegetations were decreased by 16.4%~32.8%. In addition, among the proportion of soluble nitrogen in TN, only Hippophae rhamnoides NO_3—N accounted for the highest proportion of TN, which was 1.2 times higher than that of wasteland. Correlation analysis showed that the soluble nitrogen component was more affected by TN and MBN than SOC and MBC. In summary, different vegetations had great impact on the soluble nitrogen content, density and the proportion of total nitrogen. Among them, Picea asperata and Hippophae rhamnoides had the better effect on increasing nitrogen availability.

Abstract:In order to explore the impact of microplastics on soil water retention, 1 mm and 25 μm polyethylene microplastics (PE-MPs) were selected. After the soil culture, the soil moisture characteristic curves under different treatments were measured by the high-speed centrifuge method, and the Gardner model was used for fitting analysis. The results showed that: (1) A small amount of PE-MPs (0~5.00 g/kg) accumulated in the soil could enhance the soil water holding capacity, but when the cumulative amount exceeded a certain threshold (5.00~50.00 g/kg), it would lead to a significant reduction in soil water holding capacity. (2) The large accumulation of 1 mm PE-MPs had a more significant reduction effect on soil water holding capacity; a small amount of 25 μm PE-MPs had a more significant increase effect on soil water holding capacity. (3) After invading into soil, the 1mm PE-MPs mainly affected the macropores and effective pores, and had a greater impact on the effective soil moisture content; while 25 μm PE-MPs mainly affected the micro pores and had a greater impact on the wilting coefficient. This study can provide a theoretical basis for water migration simulation and agricultural ecological risk assessment in areas with high agricultural film residues.

Abstract:The application of organic fertilizer is one of the important measures to improve the quality of tea and increase the yield of tea. The utilization of cow manure resources can help to reduce the pollution of the agricultural ecological environment. In order to explore the impact of cow manure organic fertilizer on the yield and quality of tea, through two consecutive years of field trials (2019—2020), the effects of different ratios of cow manure organic fertilizer replacing chemical fertilizer on the internal and external quality and yield of Lu’an Guapian Wuniuzao tea and the soil fertility of tea gardens were studied, and the suitable ratio of cow manure organic fertilizer replacing chemical fertilizer for tea gardens was selected. The results showed that the yield of Wuniuzao tea was the highest in all chemical fertilizer treatments, at 821.87 kg/hm², followed by the treatment of organic fertilizer with cow manure completely replacing chemical fertilizers, at 817.13 kg/hm². With the increase in the replacement ratio of cow manure organic fertilizer, the yield of Wuniuzao tea showed an upward trend, and the incremental output of Wuniuzao tea was 20.40%~44.01% in the fertilization treatment; In treatments of the organic fertilizer of cow manure replaced 70% nitrogen fertilizer and the organic fertilizer of cow manure replaced all nitrogen fertilizers, the internal composition and sensory quality of Wuniuzao tea all scored the best; The replacement of chemical fertilizers with cow manure organic fertilizer could increase the pH of tea garden soil. With the increase of the replacement ratio of cow manure organic fertilizer, soil organic matter and total nitrogen content all showed an upward trend, and alkaline nitrogen, available potassium, and available phosphorus content all showed an increase first and then declining trend, and reached the highest under the treatment of cow manure organic fertilizer replacing 70% nitrogen fertilizer; Cow manure organic fertilizer replacing chemical fertilizer increased the activity of tea garden soil urease, invertase, acid phosphatase and protease, and the soil enzymes activities were the highest under treatment that cow manure organic fertilizer replaced 70% nitrogen fertilizer. Comprehensively considering the effects of replacing chemical fertilizers with cow manure organic fertilizers on the yield, quality, biological characteristics, and soil fertility of Wuniuzao tea, replacing 70%-100% nitrogen fertilizers with cow manure organic fertilizers is a better model for replacing chemical fertilizers with organic fertilizers in the tea garden system.

Abstract:With the change of net primary productivity in a natural forest of Castanopsis carlesii in subtropical region under climate change, litter and plant root inputs will also change, which will significantly affect soil microbial community. In this study, the Detritus Input and Removal Treatments (DIRT) had been set up in a natural C. carlesii forest for seven years. In July 2019, soils of two layers (0—10, 10—20 cm) indifferent treatments (control, removal of above-ground litters, removal of roots, no input of litters, and addition of double above-ground litters) were collected to measure microbial phospholipid fatty acid (PLFA) contents. The ratio and diversity of microbial groups were calculated to further reveal the influencing mechanism of litter and plant root inputs on soil microbial community composition and diversity in a subtropical natural C. carlesii forest. The results showed that: (1) The PLFA content of microorganisms in the 0—10 cm soil layer for different treatments was about twice that in the 10—20 cm soil layer. (2) The addition or removal of litters reduced the contents of gram-positive bacteria, gram-negative bacteria, actinomycetes and other bacteria to varying degrees, but had no effect on arbuscular mycorrhizal fungi. The root removal reduced the PLFA content of arbuscular mycorrhizal fungi significantly. (3) Shannon-Wiener and Simpson diversity indices of the microbial communities were not affected by different treatments. Litter removal reduced the richness of soil microbial community and improved the evenness. The content and distribution of microbial community in 0—10 cm soil layer were greatly affected by the change of litter input. (4) Plant roots improved the content of fungi, while litter input mainly changed bacterial abundance and structure. Soluble organic carbon and mineral nitrogen were the main factors that affect the microbial community composition and diversity. There fore, litter and root inputs affected soil microbial community through the change of soil properties. The results can provide a scientific basis for understanding the effects of interactions among plants, soil, and microorganisms on forest productivity.

Abstract:In order to explore the impact of optimized nitrogen application on the carbon and nitrogen footprint of spring maize farmland ecosystem under shallow buried drip irrigation in the Xiliaohe Plain, a 2-year continuous positioning experiment was used from 2019—2020 in the Agricultural High-tech Demonstration Park in Horqin District, Tongliao City, Inner Mongolia. The conventional constant nitrogen topdressing with flood irrigation was used as the control (CK). Two treatments were set up under shallow buried drip irrigation, constant nitrogen topdressing (T₁) and optimized nitrogen topdressing (T₂: 70% of constant nitrogen topdressing), to study the effects of different irrigation and nitrogen fertilizaiton methods on spring maize yield, economic benefits, carbon and nitrogen footprint. The results showed that compared with CK, the T₁ and T₂ increased the maize yield, while improved the economic benefits of farmland (P<0.05). Soil respiration CO₂ emissions were the main source of farmland carbon footprint, accounting for 43%~44%. Chemical fertilizers were the main source of carbon emissions from agricultural production materials, accounting for 36%~43% of the total carbon emissions from production materials; nitrogen fertilizer application is the input of nitrogen footprint, accounting for 93%~95%. The net carbon values of farmland ecosystem under shallow buried drip irrigation had no significant difference between T₁ and T₂ treatments, but compared with CK, both were increased by 23.79% and 32.67%, respectively. The carbon efficiency of T₂ treatment was the highest, which was significantly higher than T1 and CK treatments (P<0.05). The nitrogen balance in T₂ was the closest to zero, which was significantly lower than T₁ and CK (P<0.05). The effective nitrogen input level was the highest in T₂, which was significantly higher than T₁ and CK (P<0.01). On the whole, the optimized nitrogen topdressing T₂ treatment under shallow buried drip irrigation reduced the carbon and nitrogen emissions of the farmland ecosystem in the Xiliao River Plain, improved the carbon efficiency and the effective utilization of nitrogen input, and ensured the maize yield and economic benefits. It is the optimal water and nitrogen management strategy for spring maize in the Xiliao River Plain, taking into account the high yield, high efficiency and ecology.

Abstract:In this study, Pinus yunnanensis communities and their soils in the two places (phosphorus-rich area and phosphorus-poor area) with large differences in phosphorus content in Central Yunnan were taken as the research objects. The Hedley phosphorus classification revised by Sui was used to study the available phosphorus characteristics of soil phosphorus and other soil nutrient factors, and the structure and differences of two types of P. yunnanensis communities were analyzed. The results showed that the total phosphorus content in the phosphorus-rich area was significantly higher than that in the phosphorus-poor area. Although the contents of active phosphorus (H₂O—P_i, NaHCO₃—P_i, and NaHCO₃—P_o) were lower than 10% in both areas, the active phosphorus content in the phosphorus-rich area was significantly higher than that in the phosphorus-poor area. In the phosphorus-poor area, the content of organic phosphorus was higher than that of inorganic phosphorus, but it was the opposite in the phosphorus-rich area. The contents of other soil nutrients such as total nitrogen and organic carbon in the phosphorus-rich area were also significantly higher than those in the phosphorus-poor area. The forest density, Shannon-wiener index, Simpson index and Pielou index of P. yunnanensis community in the phosphorus-rich area were all higher than those in the phosphorus-poor area, while the average plant height, average DBH and crown width were all lower than those in the phosphorus-poor area. The growth and development of P. yunnanensis communities in phosphorus-poor areas and phosphorus-rich areas were related to nutrition strategies. In phosphorus-deficient areas, plant communities carried out a tight phosphorus cycle to maintain normal growth. Phosphorus mainly used by plants and microorganisms came from the mineralization and dissolution of organic phosphorus, and the phosphorus loss was minimized in the biogeochemical cycle. However, in areas where phosphorus was extremely abundant, plant and microbial communities were more inclined to transfer phosphorus from soil ores to the biogeochemical phosphorus cycle. For local plants and microbes, tight phosphorus recovery was irrelevant. The significant difference in the community structure of P. yunnanensis between the two places was closely related to the phosphorus content on the ground. Phosphorus-rich areas were rich in soil phosphorus and other nutrient resources, which was able to maintain more kinds of plants and correspondingly reduce the ecological advantages of P. yunnanensis in the communities. Accordingly, phosphorus had become a limiting factor in phosphorus-poor areas, and other nutrient resources were also relatively short, which could not support a higher level of plant diversity. P. yunnanensis had a higher ecological advantage because of its strong competitiveness.

Abstract:A better hydrological model can be developed by coupling and accurately simulating the behavior of farmers’ irrigation, which can be adopted to quantify the influence of farmers’ irrigation on the hydrological cycle in canal-well combined irrigation district. In this paper, Baojixia irrigation district in Shaanxi Province was taken as an example, the question naire and interview methods were adopted first to collect data regarding to agricultural production and farmers irrigation practice. Then the factors affecting irrigation water demand and hydrological processes were analyzed. Finally, a Hydrological-Crop-Livelihood-Utility Model (HCLU) was developed by using Python language, which included hydrological, crop, livelihood and utility modules. In this model, hydrological processes, irrigation practices and crop management had been fully connected to quantify the impacts of irrigation on hydrological cycle and relationship between crop yield and irrigation. This model could be very helpful in terms of providing strong technical support for the sustainable management of water resources in the irrigation district and the adjustment of agricultural planting structure.

Abstract:The increase of phosphorus concentration in water is easy to made ecological problems such as the algae multiply greatly. Phosphorus load reduction has always been the key work of water environment treatment. Focusing on phosphorus load reduction and takes the Shahe reservoir basin upstream of Beijing Urban sub center as the research object, the SWAT model is used to analyze the effect of 24 items source control process interception ecological restoration measures of 4 categories on phosphorus load reduction. The results showed that: (1) The reduction efficiency of total phosphorus is in the order of withdrawing from livestock and poultry breeding> decentralized sewage treatment> ecological bank protection> grass ditch, vegetation buffer zone> urban runoff control> saving medicines and fertilizers, and improving the understory structure. The benefits of source control measures such as withdrawal from livestock and poultry breeding and decentralized sewage treatment are very significant. (2) It is recommended to adopt 5m wide ecological ditches, orchard: a vegetation filter belt with a filter belt area ratio of 10:1, no herbicides, a 50% reduction in the amount of organic fertilizer, a 100% resource utilization of aquaculture waste, and a 30% reduction in the amount of sewage measures to reduce the agricultural production process phosphorus load generated. Reduce the phosphorus load generated by urban non-point source pollution by increasing the pervious paving rate by 20% and increasing the dispersive pollution treatment rate by 40%. The river is recommended to adopt high-coverage ecological bank protection and 5m wide river buffer zone. (3) Reduce the phosphorus load of agriculture-towns-rivers in space, and systematically manage the major ecological elements of mountains-rivers-forests-farmlands-lakes-grasslands. After the measures are implemented, the total phosphorus load reduction rate can reach 53%, and the area of watersheds with total phosphorus reaching the IV standard will increase 8.6%, the effect is particularly remarkable.

Abstract:This study investigated the characteristics of heterogeneity and non-uniformity of soil particle size distribution in semi-arid grasslands after grazing exclusion, to evaluate the influence of grazing exclusion on the distribution of soil particle size of grassland. Our results are expected to provide support for the rational restoration and management of degraded grasslands. We examined the changes in soil particle size distribution using the multi-fractal theory at different layers (0—10 cm, 10—20 cm, 20—40 cm, 40—60 cm) along a 35-year chronosequence following grazing exclusion of grassland in Yunwu Mountain, Ningxia autonomous region, and revealed the dominant drivers for the variation of soil particle size. The results showed that grazing exclusion resulted in a reduction of soil bulk density, while an increase in underground biomass, soil nutrients contents such as organic carbon, total nitrogen, and water content, and these values peaked at 27 years after exclusion. Changes of multifractal spectral functions (Δf > 0) showed that the soil was dominated by particles with larger size, and the sand content accounted for 69.29% of total particles at the late period of exclusion (35 years), which was significantly higher than that in the early period (10 years). The capacity dimension (D₀) increased with the exclusion years, ranging from 0.866 to 0.891, The information entropy dimension (D₁) and the correlation dimension (D₂) showed a trend of first increasing and then decreasing, and increased with the soil depth at the 10-year and 15-year sites, while decreased with the soil depth at the 35-year site. D₁/D₀ decreased with soil depth, ranging from 1.012 to 0.904. There was a significant positive correlation between soil particle size distribution and soil organic carbon, indicating that soil organic carbon was the main factor affecting the particle size distribution. Our results indicated that 27-year exclusion could improve the soil nutrient levels and soil structure status, but a long-term exclusion was not conducive to the restoration of degraded grassland in the semi-arid region.

Abstract:To solve Jiangxi tungsten and other heavy metal pollution problems, an indoor simulated acid rain leaching test was conducted in this study. In the test, we studied the fixed effect of soil amendments such as rice husk biochar (BC), natural zeolite (ZE) and rice husk biochar-natural zeolite (CO) on the soil Pb, Cd and W under the conditions of acid rain with different pH (3.1, 4.5 and 5.8). The results showed that acid rain increased the leaching risk of heavy metals, and the lower the pH, the greater the risk. The addition of BC, ZE and CO effectively improved the acid buffering capacity of soil, and increased the pH of the leaching solution by 0.53, 0.23 and 0.58 units on average, respectively, and increased the soil pH by 0.27, 0.09 and 0.17 units on average after leaching. After leaching of simulated acid rain with pH=4.5 and pH=5.8, the total leaching amounts of Cd and Pb in CO treatment were significantly lower than those in untreated soil, and decreased by 32.1%, 38.0% and 36.0%, 32.7%, respectively, compared with untreated soil. W was different from Cd and Pb. Under the condition of simulated acid rain with pH=3.1, the addition of amendments had no significant effect on the total leaching amount of W. When the pH of simulated acid rain were 4.5 and 5.8, the total leaching amounts of W increased by 44.3 μg/L and 53.8 μg/L in the treatment of applying biochar alone, respectively. However, biochar combined with zeolite treatment reduced the total leaching amounts of W by 6.0 μg/L and 7.1 μg/L, respectively. In conclusion, biochar combined with zeolite could more effectively prevent leaching loss of Pb, Cd and W from contaminated soil under acid rain conditions, which could provide a reference for prevention and control of heavy metal pollution in tungsten ore areas.

Abstract:In order to explore the effects of salt and drought stress on the distribution of nitrogen in the soil and cotton growth, the distribution of total nitrogen, nitrate nitrogen and ammonia nitrogen in the soil and the growth of cotton under drought conditions under different salinity conditions in drip irrigation areas were studied through test pit tests. The experiment set up three water salinity levels with conductivity (EC) of 3 (T1), 6 (T2), 9 (T3) dS/m respectively, and three irrigation volumes of 2 700 (W1), 3 600 (W2), 4 500 (W3) m³/hm² respectively (4 500 m³/hm² was the local recommended irrigation amount). The results showed that when the soil salinity was greater than 3 dS/m, the total soil nitrogen accumulation was significantly higher than the lower salinity (P<0.05), and soil salinity had a greater impact on the growth of cotton during flowering. In addition, the volatilization of ammonia nitrogen in the soil was directly proportional to the soil salinity gradient. The leaching loss of soil nitrate nitrogen was proportional to the amount of irrigation water. Compared with the nitrate nitrogen leaching loss of normal irrigation amount, the impact of water stress on cotton yield was more serious (P<0.01). As the depth of the soil layer increased, the soil alkaline nitrogen decreased at a rate of 8% per 20 cm soil layer. The ¹⁵N residue rate in the soil of each treatment was 11%~40%, which increased with the increase of soil salinity, and decreased with the increase of irrigation amount, which was proportional to the total nitrogen content of the soil and was inversely proportional to the cotton yield. To sum up, T1W3 was more conducive to the utilization of nitrogen fertilizer in cotton and the improvement of yield. It is recommended that the soil salinity of cotton in the drip irrigation area should be less than 3 dS/m, and the irrigation volume be 4 500 m³/hm². The amount of fertilization could be appropriately increased during the flowering period to stabilize the yield.

Abstract:Taking peach orchard as the research object, the effect of green manure on soil phosphorus fractions and phosphorus turnover characteristics were investigated by Tiessen’s phosphorus fractionation method. There were three treatments, including green manure utilization as surface cover (SC), buried underground (BU) and clean tillage control (CT). Soil samples from 0—20 and 20—40 cm were collected after green manure utilization for 1, 4, and 7 years, to measure the content of total phosphorus, labile phosphorus pool (Resin-Pi and NaHCO₃—P), moderately stable phosphorus pool (NaOH—P) and stable phosphorus pool (Dil.HCl—P_i, Conc.HCl—P and Residual—P).The results showed that, compared with CT, SC and BU increased soil total phosphorus, Resin-P_i, NaHCO₃—P, NaOH—P and Residual—P contents, and decreased Dil. HCl—P_i and Conc. HCl—P contents in each sampling year. These differences were more pronounced with the increase of green manure utilization time. And, the BU showed the higher phosphorus availability than SC and the green manure mainly affected 0—20 cm soil layer. After seven years of cultivation and utilization of green manure, compared with CT, the contents of Resin—P_i, NaHCO₃—P, NaOH—P and Residual—P of BU were significantly increased by 48.82%~128.41%, 145.93%~231.16%, 206.26%~590.06% and 34.67%~37.66%, respectively, and the contents of Dil. HCl—Pi and Conc. HCl—P were significantly reduced by 12.37%~15.79% and 43.72%~91.39%, respectively. In summary, compared with CT, green manure utilization could significantly increase the proportion of soil labile and moderately stable phosphorus pool, and significantly decrease the proportion of stable phosphorus pool. Moreover, with the increasing green manure utilization years, the proportion of soil labile and moderately stable phosphorus pool also increased, while the proportion of stable phosphorus pool decreased. This study shows that the cultivation and utilization of green manure in orchards could effectively promote the mobilization and turnover of insoluble phosphorus and improve the bioavailability of soil phosphorus.

Abstract:In order to explore the effects of vegetation types and growing season stages on ecological stoichiometric characteristics of soil carbon, nitrogen and phosphorus, reveal the nutrient limitation and circulation law of terrestrial ecosystem in Loess Hilly Area,taking the typical grassland, Medicago Sativa land, Hippophae rhamnoides shrub land, Xanthoceras sorbifolium woodland and Picea asperata wood land as the research objects in Loess Hilly Area, we analyzed the contents of organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) of the 0—60 cm soil layer and their stoichiometric ratio characteristics as well as the differences between vegetation types and growth season stages. The results showed that: (1) The contents of SOC, TN and TP of arbor forest land were significantly higher than those of shrub grassland (0.7%~39.7%) in the whole growing season(P<0.05), and the contents of SOC and TN of five vegetation types gradually decreased with the growth of vegetation. The content of TP had a certain accumulation at the end of growing season. (2) In the whole growing season, the mean stoichiometric ratios (C∶N, C∶P and N∶P) of the five vegetation types were 24.70, 77.56 and 4.26, respectively. The C∶N and C∶P were larger than the national average (12.3, 61.0), while the N∶P was smaller than the national average (5.2). There were significant differences in soil stoichiometric ratio between shrub land and wasteland, but there was no significant difference in soil stoichiometric ratio between arbor forest land and in soil C∶P and N∶P between grassland. (3) The soil C∶N had good stability in time. At the same time, the soil stoichiometric ratio of each vegetation type in the growing season stage followed the order of the peak period of the growth season > the early period of the growth season > the end of the growth season. However, the comparison trend of N∶P (6.37) under the peak period of the growth season and C∶P (40.84) under the end of the growth season were opposite to those of the whole growing season and the national average. Vegetation type and growing season stage had a certain impact on soil nutrients and stoichiometric characteristics. Meanwhile, vegetation growth in Loess Hilly Area was limited by soil N rather than soil P. Therefore, nitrogen and phosphorus fertilizer should be reasonably applied according to the actual situation of vegetation type and growing stage, so as to help soil nutrient retention and accelerate the process of ecological restoration.

Abstract:The standardized precipitation index (SPI) and the standardized runoff index (SSI) were calculated using the monthly precipitation and runoff from 1970 to 2016 in central Guizhou, that characterize meteorological and hydrological droughts respectively. The dynamic characteristics of meteorological and hydrological drought in different time scales were analyzed by using run theory, the propagation time of meteorological drought to hydrological drought on different time scales was explored by using cross correlation function and drought propagation threshold. The results showed that: (1) In the past 47 years, the trend of meteorological and hydrological aridity in central Guizhou has been on the rise. The frequency of severe and extreme drought increased, and the characteristics of meteorological and hydrological drought were synchronous in a long time scale; (2) Drought propagation time (PT) was different in different seasons. PTs in spring were 1 to 5 months, PTs in summer were 1 to 3 months, PTs in autumn were 1 to 4 months, and PTs in winter were 1 to 3 months. (3) Under the influence of topography and geomorphology, the PTs of different time scales were different. On the 3-month time scale, the PTs of Yangchang, Gaoche, and Maiweng were 1.36, 2.00, and 1.58 months; on the 6-month time scale, the PTs were 2.75, 2.55, and 3.00 months; on the 12-month time scale, PTs were 3.33, 2.56, and 7.17 months.

Abstract:To study the effects of passivating agents combined with foliar fertilizer on Cd accumulation in rice plant, field plot experiments were carried out in typical Cd contaminated soil in Zhejiang. Foliar fertilizer containing Si and multi-element (DYS) were sprayed base on three soil treatment modes, which were control (CK), lime 4 500 kg/hm² (LM) and lime+biochar 1∶1 mixture 9 000 kg/hm² (LC), respectively. The results showed that compared with CK, Cd content in brown rice decreased by 70.1% and 88.3% in the treatments of LM and LC, respectively. LM combined with foliar fertilizer containing Si and DYS further reduced Cd content in brown rice by 45.3% and 28.9%, respectively, while LC combined with foliar fertilizer containing Si and DYS further reduced Cd content in brown rice by 14.5% and 13.7%, respectively. Compared with LM or LC, the addition of foliar fertilizer reduced straw-grain Cd transfer by 42.4%~62.7%, increased Cd content in straw by 81.9%~123.0%, then reduced Cd content in grain by 14.6%~64.2%. Compared with CK, both treatments of LM and LC significantly increased soil pH, reduced soil DTPA-Cd, and the effect of LC treatment was better. Furthermore, compared with CK, soil microbial carbon, organic matter, activities of urease and sucrose increased by 6.08%, 7.92%, 11.90% and 0.72% in the treatment of LC, respectively, while the above parameters decreased by 8.33%, 140.30%, 29.20% and 12.10% in the treatment of LM, respectively. The content of soil clay reduced by 5.73% and 4.53% in the treatments of LM and LC, respectively. In the treatment of LM, the content of sand increased by 29.70% and the content of silty sand decreased by 11.70%. In the treatment of LC, soil sand reduced by 1.50%, while silty sand increased by 2.17%. All results showed that LC or its combine with spraying foliar fertilizer could effectively reduce Cd in rice and maintain the healthy development of soil quality.

Abstract:The soil in the Yellow River Delta is featured with poor infiltration and high salinity. Sand incorporation into saline soil can promote disintegration of saline soil clods and improve the soil texture and structure, so as to improve soil infiltration and soil water and salt movement in the soil profile. This study used the saline soil clod in the Yellow River Delta as the experimental materials to investigate the effect mechanism of sand incorporation into saline soil on soil clod disintegration and soil salt leaching under three sand incorporation rates: CK (0), S1 (20% sands), S2 (50% sands), with soil clod composition <1 mm (20%), 1~2 mm (28%), 2~5 mm (34%), and 5~10 mm (18%). The effects of sand incorporation rates on the disintegration of saline soil and its effect on water and salt transports during two consecutive infiltrations were studied. The contents of > 0.25 mm soil clods in S1 and S2 soils were obtained by dry and wet sieving methods. The results indicated that the contents decreased by 17.92%, 15.50% and 51.45%, 32.00%, in S1 and S2 soils respectively, compared with the control group. Under different sand incorporation rates, the wetting front and cumulative infiltration were in the order of S2 > S1 > CK. And the stable infiltration rates of S1 and S2 during the first and second infiltration processes increased by 60.00%, 66.67% and 400.00%, 900.00%, respectively, compared with the control group. The salt leaching rate of the same soil depth increased with the sand incorporation rates. When the sand incorporation rate was 50%, the leaching depth increased by 33.3% and 45.45% compared with 20% incorporation rate and the control group, respectively. The salt leaching amount increased by 1.19%~19.01% and 4.21%~77.52%. In a word, saline soil mixed with sand can effectively promote the salt leaching of saline soil to improve the infiltration rate and salt leaching efficiency. This study can provide a reference basis for saline-alkali soil improvement.

Abstract:In this study, the effects of different organic materials on the salinity and dissolved organic carbon (DOC) of leachate and the salinity, organic matter and microbial carbon and nitrogen in different depths of soil were studied by soil column simulation test, including five different treatments: organic silicon functional fertilizer (WO), particle organic materials (YP), powder organic materials (GG), 50% particle organic materials and 50% powder organic materials mixed respectively (YG) and no organic materials (CK). The results showed that the addition of organic materials increased the EC value and water-soluble Ca²⁺, Mg²⁺ and Na⁺ concentration in the leachate. The contents of salt ions leached by YP treatment were the highest, but the content of DOC in the leachate treated by WO was the lowest. Compared with CK treatment, WO treatment significantly increased the water-soluble Ca²⁺, Mg²⁺ and K⁺ contents in each depth of soil layer, significantly reduced the pH, exchangeable Na⁺, exchangeable solium percentage (ESP) in each depth of soil layer, and water-soluble Na⁺, sodium absorption ratio (SAR) in 0—20 cm soil layer, but there was no significant difference in pH, EC and salinity between other organic materials and CK treatment. Leaching moved the soil salt from the surface (0—20 cm) to the deeper layers. After leaching, EC value, water-soluble total salt, exchangeable Na⁺ and ESP increased with the increase of soil depth. Compared with CK treatment, GG and YG treatment significantly increased the content of organic matter in 0—20 cm soil layer by 23.97% and 20.53%, respectively. These results could provide a theoretical data reference for the changes of salt and organic matter in the process of saline-alkali soil leaching with the addition of organic materials.