Abstract:Radar rainfall measurement with high spatio-temporal resolutions are useful in monitoring the small and middle scale rainfall systems and estimating the precipitation intensity distribution. Research on the application of radar precipitation data in the soil erosion has been conducted all throughout the world during the past decades. This study reviewed references on the approaches for obtaining the rainfall intensity from the radar reflectivity factor, compared the conversion relationships (Z=aI^b) between radar reflectivity factor (Z) and precipitation intensity (I) in different regions of China, and summarized the progress of applying radar precipitation field data in the monitoring and assessment of soil erosion based on the empirical and physical models. Results indicated that a significant negative correlation were found between a and b, and the ranges of a and b varied from 10 to 400 and 1.2 to 3.8, respectively. Southwest China was characterized with the largest a. East China and North China had the greater b than the other regions. Compared with stratiform and convective-stratiform mixed precipitation, cumulus convective precipitation had the greater a and lower b. Various studies have showed that the real-time, high spatiotemporal resolution of radar data can increase the efficiency and accuracy of soil erosion monitoring and assessment. Finally, the application of radar rainfall data in soil erosion models was prospected.

Abstract:Phosphorus is easy to be fixed and precipitated in the soil. Under the condition of low phosphorus utilization rate of plants, over-fertilization will lead to waste of phosphorus fertilizer, which may lead to eutrophication of water body and non-point source pollution through surface runoff, groundwater dissolution, etc., which has a great impact on human production and life. Combining arbuscular mycorrhizal fungi (AMF) with plants, the symbiotic mycorrhizal fungi formed could significantly enhance the uptake and utilization by plants. This paper analyzes and summarizes the research progress in four aspects:the mechanism of AMF promoting plant phosphorus uptake, the molecular mechanism of AMF promoting plant phosphorus uptake, the influence of root exudates under the action of AMF on plant phosphorus utilization, and the influence of rhizosphere microorganisms on AMF phosphorus utilization.AMF can expand the range of nutrient uptake by plants by changing the root morphology of host plants and the formation of mycelium network; The release of organic acids, phosphatases, protons and other root secretions changed the soil structure and physicochemical properties, and decreased the solubility of insoluble phosphate in the soil under the combined action of rhizosphere microorganisms; Specific expression of related phosphorus transporter genes was induced to improve the ability of phosphorus transport in plants and promote their absorption.

Abstract:The universal soil loss equation (USLE) and Chinese soil loss equation (CSLE) are widely used for soil erosion evaluation. Different methods for calculating slope length factor could cause differences in topographic factors and soil erosion. The purpose of this study was to evaluate the effects of different methods for calculating slope length factor (L) on topographic factor and then on the soil erosion. The 1:10 000 topographic maps from five regions of Nenjiang, Wuqi, Kaixian, Huailai and Changting were selected and 5 m×5 m DEMs were generated. The segment slope length method (SSLM) and the catchment area method (CAM) were used to calculate the slope length factor. The CSLE was used to calculate soil erosion. The results showed that the average L factor value and spatial variation from the CAM were greater than those from the SSLM. The area with low L factor values had less difference and the area with high L factor value greater difference between the two methods. The proportions of soil erosion area calculated by the two methods in different terrain areas were not obviously different. However, the soil erosion intensities showed significant differences between the two methods. The results could provide data support and theoretical basis for the study of soil erosion topographic factors and soil erosion assessment in different topographic regions.

Abstract:In order to explore the drop pit development on soil-rock mixed colluvial deposit slopes, a scouring test was conducted in laboratory. Four soil-rock mixed colluviums (0, 10%, 30%, 50% gravel in mass ratio) under different flow discharges (2, 4, 8, 12 L/min) were tested.The results were as followed:the number of drop pit varied from 3 to 17, the average depth of drop pit was between 1.10 to 5.93 cm, and the profile form indices were between 2.97 and 19.97. The number of drop pit, the depth of drop pit, and the profile form indices all showed the increasing trend overall with the increase of scouring duration, whereas the maximum value appeared in some slopes at 5 min or 7.5 min. All drop pit parameters first increased and then decreased with the increase of flow discharge as a whole, and the maximum value appeared under the discharge of 8 L/min. The number of drop pit, the depth of drop pit, and the profile form indices increased with the increase of gravel content.The influence of flow discharge on the all parameters of drop pit was greater than those of gravel contents. Drop pit parameters were significantly correlated with flow velocity,resistance coefficient and Manning roughness coefficient. Shear stress was the best hydrodynamic parameter to describe the development of drop pit development as a linear function.

Abstract:This study aimed to explore the characteristics of nitrogen loss in different growth periods of crops, which could provide theoretical basis for the prediction and effective control of nitrogen loss in dry sloping land of red soil. Under natural rainfall conditions, lysimeters were continuously used to collect the data about surface runoff, seepage water and nitrogen output process on dry slope of Quaternary red soil in northern Jiangxi. The results showed as follows:(1) Runoff generation of peanut land on dry slope of red soil mainly occurred at the flowering period with the most abundant rainfall. Leakage water was the main form of runoff in peanut growing period, accounting for 64% of the total runoff. (2) Leakage water was the main path of nitrogen loss in all growth periods, primarily in the form of soluble nitrogen, occupying 54% to 99% of total nitrogen (TN) loss. Nitrate nitrogen (38%~50% of TN) was the main component of nitrogen loss in seepage water during all periods except the ripening period of full fruit. (3) Nitrogen concentrations in surface runoff and seepage water in the seedling period and flowering period were larger than those in other growth periods, while the nitrogen loss in them was the largest in flowering period. Therefore, the key periods for controlling nitrogen loss in peanut land on dry slope of red soil were the seedling stage with the lowest vegetation coverage and the flowering stage with the most concentrated rainfall. Besides, the crucial way to reduce nitrogen loss in the land was controlling nitrogen leaching loss such as nitrate nitrogen.

Abstract:This study explored the effects of four furrow slopes (0°, 9°, 18° and 27°) on the concentrations and losses of PO₄^3--P, NO₃^--N and NH₄⁺-N through simulated rainfall experiments, and evaluated eutrophication risk of the runoff by the ratios of Inorganic-N/PO₄^3--P, NH₄⁺-N/PO₄^3--P, and NH₄⁺-N/PO₄^3--P. The results were as follow:(1) PO₄^3--P, NO₃^--N, and NH₄⁺-N concentrations changed in the shape of wavy serrated shape with rainfall time under four furrow slopes. As for losses, their maximum value (16.60, 1 020.73, 48.35 mg) appeared in 0°, 0°, and 9° when they increased firstly and then changed in zigzag shape with rainfall time. (2) Under different furrow slopes, PO₄^3--P and NH₄⁺-N losses in runoff water were in order of 0° > 9° > 27° > 18°, whose concentration maximum value (0.50, 1.08 mg/L) and minimum value (0.37, 0.76 mg/L) appeared in 9° and 18°. NH₄⁺-N concentration and losses maximum value (30.68 mg/L and 64.16 mg/m²) and minimum value (21.78 mg/L and 42.22 mg/m²) appeared in 0° and 18° in runoff water. (3) The ratios of Inorganic-N/PO₄^3--P and NH₄⁺-N/PO₄^3--P showed that four furrow slopes output runoff all had eutrophication risk, and the 0° output runoff of that was the highest and the 27° was the lowest. These findings would provide scientific guidance for evaluation, prediction, and control of soil and water loss and nutrient loss in contour ridge system.

Abstract:In order to reveal the contribution of colloidal phosphorus to the loss of total phosphorus, we carried out a field experiment to collect the water of paddy surface and ditches under typical rainfall events. According to the actual weather conditions, we selected a typical rainstorm event (48 mm/h) and eight rainfall events with different intensities of 8, 9, 19, 23, 23, 32, 36, and 49 mm/h. The results showed that:(1) Phosphorus loss in the surface water and paddy field drainage was mainly composed of particle phosphorus. In the total phosphorus passed over the 1 μm filter, the loss of colloidal phosphorus accounted for 21%~73%, even exceeding the loss contribution of true dissolved phosphorus. (2) The contribution of colloidal phosphorus in the surface water after rainfall was 9%~44%, and the contribution of colloidal phosphorus loss in paddy field drainage was 10%~16%. There was positively correlation among metal oxide colloid, organic colloid, metal oxide-organic colloid and colloidal phosphorus loss contribution. The correlation coefficients in the surface water were 0.544, 0.635, 0.781 (p<0.05), and the corresponding values in the drainage in the paddy field were 0.734, 0.350, 0.747 (p<0.05), respectively. They were the important forms of colloidal phosphorus in runoff. (3) Fertilization reduced the contribution of colloidal phosphorus loss by affecting conductivity and ionic strength, while rainfall intensity increased the contribution of colloidal phosphorus loss by affecting pH value. The R² value of linear regression coefficient of rainfall intensity and colloidol phosphorus concentration of drainage in the paddy field was 0.75, but the degree of influence on the loss of colloidal phosphorus in the surface water and rice field drainage was different.

Abstract:In the karst area of the Danjiangkou reservoir area, the nitrogen (N), phosphorus (P) and potassium (K) nutrient loss and the sediment particle size distribution characteristics of slope erosion in five vegetation cover types (arbor forest land (C1), sparse forest land (C2), farmland (C3), grassland (C4), shrub grassland (C5)) under natural rainfall conditions were observed to discuss the relationship between sediment nutrient loss and particle size distribution. The results showed that:(1) The sediment of erosion was dominated by silt (2~50 μm) and sand (50~2 000 μm). There were significant differences in the sorting of clay (0~2 μm) particles between different vegetation cover types (P<0.05). The contents of fine particles (0~20 μm) in the eroded sediment decreased with the increase of rainfall intensities. The 0~2 μm particle concentrations were concentrated in 3.08~6.62. The 2~20 μm particle concentrations were concentrated in 2.48~3.58. The 20~50 μm particle concentrations were concentrated in 1.04~1.62. The 50~100 μm particle concentrations were concentrated in 0.61~0.88. The 100~2 000 μm particle concentrations were concentrated in 0.43~1.15. The 0~20 μm particle enrichment of C4 was the largest, and the 0~20 μm particle enrichment of C3 was relatively small. (2) Among the available nutrients, the loss of available K (AK) was much higher than those of available N (AN) and P (AP). The concentrations of total P (TP) and AK of C4 were significantly higher than those of C1, C2, C3 and C5 (P<0.05). The total nutrients loss in C3 was the largest, and C1, C2, C4 and C5 had the significant effect on reducing nutrient loss. The effect of C2 on controlling nutrient loss was the most obvious. The total N (TN) concentrations were concentrated at 0.56~1.25, the NH₄⁺-N at 1.08~1.17, the NO₃^--N at 0.94~1.50, and the TP at 1.41~1.96, the AP at 5.00~8.77, the AK at 1.79~3.05. The N and P enrichment were relatively low in C3, and relatively large in C2 and C4. (3) The contents of TN, TP, AP and AK in erosion sediment were positively correlated with the contents of 0~2, 2~20 and 20~50 μm, and the correlation with 0~2 μm was significant (P<0.05). The nutrient concentrations increased as the fine particle content increased.

Abstract:In order to alleviate the serious soil and water loss of slope in Hilly-Gully Loess Region, this paper took DuanLanyao drainage loess slope in Qingshuihe County of Inner Mongolia as the research area, and adopted three vegetation carpet measures:the mixed planting of Legumes and Gramineae plants with a ratio of 1:1+coconut carpet (L₁G₁), the mixed planting ratio of 1:2 + coconut carpet (L₁G₂), and the ratio of 2:1 + coconut carpet (L₂G₁). Runoff plots were set up with slope gradients of 30°, 35°, 40° and 45°. The effects of different natural rainfall conditions and slopes on slope runoff and sediment yield were analyzed. The results showed that:(1) Vegetation carpet could effectively reduce the runoff and sediment yield of Loess slope. (2) When the rainfall intensity was 1~5 mm/h, the runoff and sediment yield of vegetation carpet measures increased with the increase of slope gradients; when the rainfall intensity was 30~50 mm/h, the runoff and sediment yield of vegetation carpet measures increased first and then decreased with the increase of slope gradients, and the peak value appeared when the slope was 40°. (3) The benefits of three vegetation carpet measures were L₁G₁ (75.11%) > L₁G₂ (49.3%) > L₂G₁ (48.11%) and L₁G₁ (87.96%) > L₁G₂ (60.96%) > L₂G₁ (58.95%), respectively. It could be concluded that L₁G₁ was an effective measure to control soil and water loss of slope in the Hilly-Gully Loess Region.

Abstract:In order to clarify the flood infiltration process in the uncontrolled engineering area, and improve the ability of flood prevention and control and the degree of flood resource utilization, the hyper-concentrated flow channel downstream of the Xitugou watershed in Yangguan, Dunhuang was selected. The field experiment and laboratory analysis were conducted to measure the different pressure heads of the river section from the upper section to the lower section of the river. Under the infiltration rate, the saturated infiltration coefficient was obtained by fitting, and the saturated infiltration coefficients at different depths were obtained by laboratory measurements. The variation of saturated infiltration coefficients of the left and right banks, centers and different depths of the riverbed was analyzed. The results showed that the saturated infiltration coefficients:upper section (0.003 1 cm/s) > middle section (0.002 9 cm/s) > lower section (0.002 6 cm/s); the saturated infiltration coefficient at different depths in the upper part was larger than that in the middle and lower sections, and the difference between the middle and lower sections was small. On the whole, the saturated infiltration coefficients on both sides of the riverbed increased with the increase of depth, and the saturated infiltration coefficients of the riverbed decreased with the increase of depth. The reason for the above results was that the sediments were deposited along the hyper-concentrated flood, the coarse sediments were deposited first, and then the fine sediments were deposited, resulting in the difference in porosity of the upper and lower sediments, and the variation of saturated infiltration coefficients in river sections and different depths. The infiltration rate was determined by different pressure heads to characterize the infiltration rate under different flood levels, the trend fitting showed that the surface infiltration rate increased linearly with the increase of flood water level.

Abstract:In order to reveal the erosion variation law of the Quaternary red clay slope under different rainfall intensities and slope gradients in mulching conditions, three representative rainfall intensities (1.0, 1.5, 2.0 mm/min) and three typical slope gradients (10°, 15°, 20°) in red soil hilly area southern China were selected. The characteristics of runoff, sediment yield and infiltration were analyzed by artificial simulation rainfall experiment. Moreover, taking 15° as an example to calculate the effect of reducing the flow and sediment on the slope. The results showed that:(1) The time producing runoff was advanced with the increase of rainfall intensities and slope gradients. The mulching had obvious hysteresis effect on the runoff yield time. However, the increase of rainfall intensities would weaken the effect of mulching on delaying runoff production. The runoff rate increased in the early stage and become stable in the later stage. (2) At the same slope gradient, the rainfall intensities increased from 1.0 mm/min to 2.0 mm/min, and the total amount of sediment yield increased by 1.89~2.96 times. When the rainfall intensity was constant, and the slope gradients increased from 10° to 20°, the total amount of sediment yield increased by 1.91~3.45 times. (3) The initial infiltration rate and the cumulative infiltration of soil decreased with the increase of slope gradients. While the increase of rainfall intensities increased the initial infiltration rates of mulched slope and reduce the cumulative infiltration. (4) Under the condition of 15°, the runoff and sediment volumes of the mulched slope decreased by 50.26% and 95.31% respectively, and the soil and water conservation effect of pine needle mulching was significant. In addition, the sand reduction effect was greater than the flow reduction effect. (5) The influence of slope gradients on the cumulative runoff and sediment yield of mulched slope was greater than that of rainfall intensities. There was a power function relationship(R²>0.97) between the cumulative runoff and sediment yield under different rainfall intensities and slope gradients. These results could provide reference for soil erosion control and ecological restoration in the red soil hilly region of southern China.

Abstract:The study of the soil wind erosion characteristics under different land use types could provide data support for the adjustment of regional land layout and the construction of ecological environment in grape planting area of Yanhuai Basin. In this paper, five land use types (grape, fruit mulberry, Cerasus humills (Bge.) Sok., no-tillage with maize stubble, tillage with maize stubble) were selected, and soil water content, soil wind erosion amount, and soil particle size were analyzed from November 2018 to March 2019 in Huailai county. The results showed that the soil water content of the five land use types decreased with the increase of time before the precipitation event, and the soil water content of the three fruit land use types decreased in the order of grape > C.humills (Bge.) Sok. > fruit mulberry. The surface soil particle size of the five land use types was mainly gravel in this study area (the content of gravel was 47%~63%). It was the major particle that lose during wind erosion when the soil particle size was 0.05~0.002 mm. The soil wind erosion amount of the five land use types decreased in order of tillage with maize stubble > grape > no-tillage with maize stubble > C. humills (Bge.) Sok. > fruit mulberry. In the process of prevention and control of soil wind erosion in this region, it is applicable to reduce near-surface wind speed, intercept wind sand, and reduce wind erosion by adjusting the layout of fruit land (for example fruit mulberry) and grape, corn land.

Abstract:In order to study the dynamic process of erosion on the loess slope in both continuous and intermittent rainfall patterns, we carried out a laboratory rainfall experiment. We used the 3D laser scanning to acquire the point cloud of the slope and generated DEM to analyze the erosion characteristics of the slope. The results showed that the DEM generated by 3D laser scanning could visually reproduce the dynamic process of slope erosion. The error of DEM generated by natural neighbor interpolation method was the smallest. At the location of 5 cm from the slope surface, the fluctuation of volumetric water content under the intermittent rainfall mode was consistent with the rainfall period. The total amount of soil loss under two rainfall patterns increased linearly after soil was saturated. The total amount of soil loss caused by intermittent rainfall (0.035 6 m³) was greater than that caused by continuous rainfall (0.024 9 m³). The soil loss process of intermittent rainfall could be seen as a combination of multiple continuous soil loss processes. Under the two rainfall patterns, the soil loss rate was unevenly distributed in space, and gradually decreased from the front to the trailing edge. Under the intermittent rainfall, the slope surface changed from the central to the front, and the process was:the front cutting → the mid-front cutting → the front and central cutting. Under continuous rainfall, the change of slope surface concentrated on the front, which was characterized by the gradual retreat of the front.

Abstract:In order to study the effects of different surface relief forms on runoff and sediment yield during slope erosion process, five kinds of surface relief treatments (mounds, depressions, Intervals mound and depression, continuous mound and depression, smooth) were set up. The runoff and sediment yield of each treatment under three rainfall intensities (60 mm/h, 90 mm/h, 120 mm/h) by field artificial rainfall experiments were analyzed. The results showed that:(1) Under three rain intensities, the initial runoff time of the smooth surface was the shortest, while the continuous mound and depression surface was the longest. The initial runoff time of intervals mound and depression surface was close to continuous mound and depression surface, while mounds surface was just a little longer than the smooth one. The runoff time of depression surface was in the middle. The shorter the initial runoff time was, the bigger the runoff volume and runoff coefficient were. (2) Under the same rain intensity, the sediment volume and sediment yield intensity of different treatments ranked as:continuous mound and depression surface < intervals mound and depression surface < depressions surface < smooth surface < the mound surface. The greater the sediment yield intensity was, the more unstable the sediment yield process was. (3) Compared to the smooth surface, the mound aggravated soil loss, while the depression reduced soil loss. When mounds and depressions were combined, the reduction of soil loss was more significant. (4) Increasing rainfall intensities weakened the effect of different surface reliefs on runoff and sediment yield. The conclusion was that the different types of surface relief affected the runoff and sediment yield significantly. Runoff occurred most easily on smooth surface, and soil loss was most serious on mound surface, as well as the conservation of soil and water was best on continuous mound and depression surface.

Abstract:This study explored the impact of the short-duration high-intensity rainfall on the erosion and sediment yield of typical karst slope farmland. The results would provide theoretical basis for the monitoring and preventing of extreme weather and soil erosion in slope farmland of karst area. The artificial indoor simulated rainfall experiment was conducted to study the erosion and sediment yield characteristics of karst slope farmland under the short-duration high-intensity rainfall. Results showed that:(1) Under the short-duration high-intensity rainfall, the surface sediment transport modulus and sediment yield of karst slope farmland increased with the increase of rainfall intensities, but there was no obvious change in the under-ground sediment transport modulus and sediment yield. The soil erosion of slope farmland was dominated by the surface, and the critical rainfall intensities of surface sediment yield were between 30~50 mm/h. (2) The proportion of surface sediment yield was greater than the underground when slope increased, and soil erosion was dominated by the surface. The transition slope of sediment yield was between 15°~20°. At 70 mm/h rainfall intensity and 5° slope, rainfall intensity might have a "negative effect" on underground soil erosion. (3) The characteristics of erosion and sediment yield on karst slope farmland were closely related to rainfall intensities and slope, but the rainfall intensity factor played the leading role. High-intensity rainfall mainly affected surface soil erosion. Therefore, the soil erosion control of karst slopes farmland should be dominated by the surface. This study is helpful to understand the impact of short-duration high-intensity rainfall on soil erosion of karst slope farmland, and to provide theoretical basis for coping with the extreme weather, controlling soil erosion, maintaining the healthy and sustainable development of the ecological environment in karst slope farmland.

Abstract:To reveal the mechanism of collapsing gully erosion from a perspective of soil mechanic, the anisotropic characteristics of shear strength and the related influencing factors for undisturbed granitic soils from a typical granite weathered soil profile in southeastern Hubei were investigated by direct shear test. In accordance with the obtained results, the cohesion and internal friction angle of granite weathered soils ranged from 3.19 kPa to 19.26 kPa and 26.50° to 32.42° at saturation, and the maximum cohesion occurred for soils in the B₂ layer, while the difference of the internal friction angle along the investigated soil profile was less significant (p>0.05).In addition, cohesion and internal friction angle with significant anisotropy were larger in the horizontal direction than those in the vertical direction. Soil physicochemical properties that influencing of shear strength varied with profile direction. Specifically, the cohesion was mainly affected by capillary porosity (r=-0.97, p<0.01) and silt content (r=0.94, p<0.05) for soils in the vertical direction, and it was conditioned by silt content (r=0.91, p<0.05) for soils in the horizontal direction. However, the significant correlation between soil physicochemical properties and internal friction angle was solely observed for soils in the horizontal direction in which the variation of internal friction angle was influenced by liquid limit (r=-0.99, p<0.05). Furthermore, the anisotropy of shear strength of granitic weathered soils was mainly affected by natural water content (r=-0.98, p<0.01), organic matter (r=-0.93, p<0.05), and plastic limit (r=-0.97, p<0.05). These results would facilitate the understanding about the formation and development of collapsing gully erosion in southeastern China.

Abstract:Soil anti-scourability of different vegetation types and the effects of plant roots on soil anti-scourability in Caijiachuan watershed of Loess Gully-Hilly Area in Western Shanxi Province were studied by using undisturbed soil scouring experiment, taking the soil of Pinus tabulaeformis forest, Robinia pseudoacacia forest, Armeniaca sibirica forest, Vitex negundo land and wasteland as research objects. The results showed that:(1) In the undisturbed soil scouring experiment, the trend of runoff of all vegetation types with the scouring time was not obvious, and the sediment concentration decreased at the beginning and then tended to be stable with time, while the index of soil anti-scourability showed a trend of increasing gradually. (2) The total root length density, root surface area density, root volume density and root biomass density of all vegetation types showed that Robinia pseudoacacia and Armeniaca sibirica forest land were larger, while Prunus armeniaca, Vitex negundo and wasteland were smaller and similar. There was a positive correlation between the total root parameters. Among the root indexes of different vegetation types with different root diameter ranges (0~0.5, 0.5~1.0, 1.0~2.0, 2.0~5.0, >5.0 mm), the root length density of 0~0.5 mm diameter root was the largest, and the root volume density of the fine roots was generally smaller than that of coarse roots. (3) Plant roots of different vegetation types can enhance soil anti-scourability. The enhancement effect was stronger in Robinia pseudoacacia and Armeniaca sibirica forestland, weaker in Armeniaca sibirica, Vitex negundo and wasteland. There were significant or extremely significant positive correlations between the root length density, root surface area density and root volume density of<1 mm diameter root and soil anti-scourability enhancement value among all plant root system indexes. There was no significant correlation between other diameter root parameters and soil anti-scourability enhancement value.

Abstract:In order to analyze the change and driving mechanism of erosion and sediment yield in the hillside area, this paper applied SWAT model to simulate sediment yield in Shouchang River Basin of Jiande City, Zhejiang Province, and calculated the landscape metrics based on Fragstats 4.2 for land use data in different years. The sediment yields in the basin were analyzed, the effects of slope, slope length, elevation, drainage area, rainfall, and landscape pattern on soil and sediment yield were discussed, and the principal components analysis was carried out. The main results were as follows:(1) The SWAT model had good applicability in the Shouchang River basin, R², NSE and PBIAS all met the simulation and ensured the accuracy of the simulation results. (2) The maximum sediment yield of the entire Shouchang River basin from 1980 to 2010 was less than 500 t/(km²·a), and the soil erosion intensity was slight and the soil erosion retention ability was good. (3) The contribution rates of four principal components of topographic factor, landscape diversity factor, landscape shape factor, and rain intensity factor to sediment yield were 51.48%, 18.51%, 10.70%, and 6.94%, respectively, and topographic factor was the main factor affecting soil erosion and sediment yield. (4) There was a significant correlation between the landscape metrics and the sediment yield, and the landscape metrics had a significant impact on the sediment yield. In the future land-use planning, the landscape characteristics should be effectively considered to improve the soil erosion in the basin.

Abstract:Rainfall characteristics and slope gradients are important factors that affect soil infiltration process, and their effects on soil infiltration characteristics may be different during the process of vegetation restoration. To discuss the effects of rainfall process parameters (rainfall, mean rainfall intensity, rainfall duration and I₃₀), inclination of slopes and vegetation coverage on the infiltration characteristics, six runoff plots of two-years abandoned grassland with the slope gradients of 5°, 10°, 15°, 20°, 25°, and 30° were selected in the hilly region of the Loess Plateau, and their soil infiltration characteristics were observed in the peak period of vegetation growth (July to September) under natural rainfall (34 rainfall event and 11 rainfall-generated runoff). The results indicated that:(1) For the 11 runoff-producing rainfall under different slope gradients, the variations of soil infiltration amount was ranged from 6.58 to 70.91 mm, the infiltration supplement coefficient was ranged from 0.83 to 1.00, and the infiltration rate was ranged from 0.22 to 19.35 mm/h; (2) The amount of soil infiltration increased linearly with rainfall capacity (R²=0.99, p<0.01) and the infiltration supplement coefficient decreased exponentially with I₃₀ (R²=0.91, p<0.01). While for the average infiltration rate, it was increased linearly with rainfall intensity (R²=0.71, p<0.01) and decreased exponentially with rainfall duration (R²=0.99, p<0.05); (3) The increase in slope gradient extended the runoff displacement, resulting in the exponential increase in the infiltration volume, the infiltration supplement coefficient, and the average infiltration rate. However, when the slope gradient exceeded 25°, the component of runoff potential energy increased along the slope direction, the runoff velocity speeds up, and the above-mentioned infiltration characteristic parameters decrease slightly. (4) The amount of rainfall showed a downward trend during vegetation growth cycle, which to some largely extent manipulated the influence of vegetation on the infiltration characteristics, so the infiltration amount decreased significantly with the vegetation coverage. In general, rainfall characteristics and slope gradients are the main factors affecting soil infiltration, and soil infiltration characteristic parameters can be expressed as the comprehensive power function equation of rainfall process parameters and slope gradients. The effect of vegetation coverage on soil infiltration characteristics was weakened as the infiltration supplement coefficient was high. This study is of great significance for the research of rainfall-runoff regulation mechanism and eco-hydrological process at slope scale.

Abstract:Intercropping is an important practice for controlling soil erosion in the world. However, knowledge on this phenomenon is not well understood, especially in flow hydraulics. A lab experiment was conducted to provide the theoretical basis for reducing erosion mechanisms in intercropping. Three cropping patterns i.e. maize monoculture (MC), potato monoculture (PC), and two rows of maize intercropped with two rows of potato (IC) were used under two surface roughness models:low ridging and high ridging, totaling six treatments. The runoff velocity, Reynolds number, Froude number, and Darcy-Weisbach resistance coefficient were measured with two rainfall intensities (40, 80 mm/h) during the experimental periods. The results suggested that:(1) The values of IC were lower than those of MC in terms of runoff velocity, Reynolds number, and Froude number. Furthermore, the resistance coefficients in IC were higher than those in MC at the same rainfall intensity. There was no difference between IC and PC in terms of runoff velocities and resistance coefficients. In early July, the resistance coefficients were 0.41~0.53 for IC and 0.09~0.10 for MC at the rainfall intensity of 80 mm/h. The runoff velocities was 0.11~0.12 m/s for IC and 0.19~0.21 m/s for MC at the same rainfall intensity.(2) The lowest runoff velocity, Reynolds number, and Froude number were observed in intercropping with high ridging, which gave the highest resistance coefficient. In early July, the runoff velocities of intercropping with high ridging, intercropping with low ridging, and maize monoculture with high ridging were 35.71%, 35.71% and 14.29% respectively lower than that of maize sole crop with low ridging at the rainfall intensity of 40 mm/h. Thereby, intercropping could increase resistance coefficient to reduce runoff velocity, which was one of mechanism to reduce erosion in intercropping and provide an important reference for understanding the mechanism of soil erosion controlling by crop cultivation. In addition, intercropping with high ridging could effectively decrease runoff velocity on the surface, and might be contributed to the soil erosion control and sustainable development of agriculture.

Abstract:Gravel covering on the surface of soils can increase water infiltration and protect the soil against erosion. However, the effects of gravel covering in purple soils was less well investigated. In this paper, the influence of gravel covering on hydraulic characteristics of slope flow on purple soils in southern China was studied under simulated scouring conditions. Different gravel covering ages from 0 to 40% under three flow rates (2 L/min, 4 L/min, 6 L/min) were set up. Results showed that:(1) Flow velocity and the Froude number decreased, but the runoff depth, flow shear stress, Darcy resistance coefficient and the Manning roughness coefficient increased with the increase of cover ages. (2) The total erosion of the slope decreased negatively with the increase of cover ages. Under the small flow rates, the reduction effect of gravel covering on erosion amount of slope flow was more obvious. (3) The flow rates did not affect the relationship between gravel coverage and total erosion on the slope.

Abstract:In order to investigate the characteristics of water and nitrogen migration under multi-point source infiltration in the muddy water-filled membrane hole irrigation, the indoor hydrophobic membrane hole infiltration device was used to test the influence of the infiltration solution (0 g/L, 1 g/L, 2 g/L, 3 g/L, and 4 g/L ammonium nitrate solution) on the infiltration laws, the occurrence time of one-way intersections and multi-directional intersections, the water content in the vertical direction of film hole centers and junctions (the plant intersection center, the inter-row intersection, and the 4-point source intersection),and the distribution law of NO₃^--N. The results showed that the cumulative infiltration and permeation time per unit area of membrane pores showed a power function relationship, the infiltration index a decreased with the increase of fertilizer concentration while the infiltration index b increased with the increase of fertilizer concentration. With the increase of fertilizer concentration, the occurrence time of one-way intersection and multi-directional intersection was advanced. At the depth of 10 cm soil, the water content of each center increased by 10.42%, 13.94%, 16.38%, and 24.74%, respectively, compared with 0 g/L treatment. The water content in each center varied with the increment of soil depth. NO₃^--N was evenly distributed in the upper layer of the soil, and showed peak at the wet front. The NO₃^--N content at the 4-poing source intersection center was higher than the other 3centers.The results provide a basis for improving the theory of water-filled membrane hole irrigation.

Abstract:After the project of returning farmland to forest and grass was implemented, the forest and grass structure of Karst Mountain vegetation was improved obviously. It is of great significance to study the infiltration characteristics of carbonate laterite in Karst Mountain in vegetation restoration for the restoration and reconstruction of karst ecosystem. The water infiltration characteristics of different negative pressure heads (-0.5, -3, -6, and -15 cm) under different vegetation covers (wild grass ground, shrub-grassland, and arbor land) were measured by disc infiltration method. The contribution rate of the hydraulic conductivity, the distribution constant of soil pore size, and the grade of pore under different negative pressures to water flow was calculated. The infiltration characteristics of carbonate laterite with different vegetation covers were clarified. The results showed that a significant differences in soil steady infiltration rate among wild grass ground, shrub-grassland, and arbor land under different water head conditions. The difference of soil steady infiltration rate increased with the increase of negative head, and the time required for soil infiltration in the test area to reach the stable infiltration state was long (about 120 min). The soil steady infiltration rate of wild grass ground was the highest (0.17 mm/min) under the condition of low head, but the arbor land was the largest (9.17 mm/min) under the high water head. There was significant difference in soil saturated hydraulic conductivity K_s among wild grass ground, shrub-grassland, and arbor land (P<0.01), and the saturated hydraulic conductivity of arbor land reached the maximum (4.62 mm/min). However, there was no significant difference in K₃, K₆, K₁₅, and Gardner α, and the saturated hydraulic conductivity K_s of carbonate laterite was only controlled by soil organic matter content and soil conductivity. The quantity and the proportion of macropores in the soil of the arbor land were significantly larger than that of the shrub-grassland and the wild grass ground (P<0.05), and the water conductivity of carbonate laterite was mainly controlled by the effect of soil macropores on water flow (>70%). These results can provide data support and practical experience for ecological restoration and water resources carrying capacity analysis of Karst Mountain in Southwest China.

Abstract:The reservoirs of Qingshuihe basin in Ningxia have important role on sediment-retaining effect, which is also an important factor to be considered in the revert calculation of sediment yield. However, how to calculate the annual sediment-retaining amount based on the total amount of sedimentation has ever been rarely reported. Based on the measured data, the basic situation was analyzed and the total sediment-retaining volume of the Qingshui River Basin reservoirs was estimated in this paper. Three factors of control area, average erosion intensity and sediment-retaining rate were introduced to establish the calculation formula for the annual sediment retention by reservoirs. Analysis based on statistics showed that there were 100 reservoirs in the Qingshuihe basin, the total capacity was 12.23×10⁸ m³, the controlled drainage area was 9 184.70 km², the total storage capacity was 1.235 billion m³, the sediment-retaining capacity was 686 million m³, and the sediment-retaining volume was 571 million m³, which accounted for 78.25% of sediment transported at Quanyanshan Hydrological Station in 1957 to 2012. The verification of the calculation results showed that the model had good calculation accuracy when the number of reservoirs was large and the distribution was relatively uniform. According to the calculation results, the sediment retaining volume of the reservoir was relatively large before 1979. Since 1960, the remaining sediment-retaining capacity of the reservoir declined. After 2000, the sediment-retaining ratio of the reservoirs remained about 83.00%, it showed that the reservoirs showed a limited capacity in the sediment-retaining.

Abstract:In this study, soils from the sites of 12 vegetation plots were sampled, and plant residue, soil bulk density, capillary porosity, non-capillary porosity and saturated hydraulic conductivity were measured to discuss their variations in different soil layers and vegetation types. Besides, the effects of plant residue and soil properties on the saturated hydraulic conductivity were detected. The results showed that:(1) Soil bulk density increased with the increase of soil depth, while plant residue, capillary porosity, non-capillary porosity and saturated hydraulic conductivity decreased. Plant residue mainly existed in the top soil of 0-10 cm, which accounted for 51.4% to 85.7% of the total plant residue. (2) Soil properties and plant residue differed from vegetation types. In general, forest had the largest plant residue, cropland had the highest soil bulk density, and shrub land had the maximum non-capillary porosity and saturated hydraulic conductivity. While no significant difference of capillary porosity was found between different land use types. (3) Saturated hydraulic conductivity decreased with the plant residue (0-10 cm) and soil bulk density, while increased with capillary porosity and non-capillary porosity. Soil bulk density (BD) and non-capillary porosity (NCP) were key factors that affect the soil saturated hydraulic conductivity (K_s), which would simulated saturated hydraulic conductivity as a nonlinear function (K_s=0.6BD^-4.717NCP^0.203, p<0.01, R²=0.63, NSE=0.50). Moreover, the shrub land of Hippophae rhamnoides L. had the maximum value of saturated hydraulic conductivity, which would promote the ability of water infiltration during the precipitation and thus had a great effect on soil and water conservation. The results of this study could provide a theoretical basis for evaluating the effects of vegetation restoration on ecological hydrological process on the Loess Plateau.

Abstract:The abrupt change of runoff series may occur in the changing environment. At present, researches on the contributions of runoff variation mainly focus on the annual scale, but pay insufficient attention to the seasonal scale. In this paper, the typical watershed of the Loess Plateau, Jinghe River Basin, was taken as the research object. Firstly, the wavelet analysis method was used to reveal the evolution of seasonal runoff series. Then the order clustering method and cumulative anomaly method were used to diagnose the variation of runoff sequence. Finally, the contributions of climate change and human activities to the seasonal runoff variation were quantified by making a comparison of slope change ratio of the fitted beeline between year and accumulative quantity. Results showed that:(1) The period of summer and winter runoff shift from small scale to large scale after the 1990s; (2) Runoff variation occur in spring, summer, autumn, and winter in Jinghe river basin are 1969, 1996, 1985, and 1990, respectively; (3) The contribution rates of human activities to runoff variation in spring, summer, autumn, and winter are 50.40%, 89.69%, 39.14%, and 84.59%, respectively. The contribution of human activities (mainly soil and water conservation measures) to runoff variation was dominant in summer and winter, which mainly affected the periodic shift of runoff after the 1990s.

Abstract:Studying the change characteristics of high-standard terrace ecological service function in loess region, discussing influence trend and potential of the project of changing mountain slop into terrace on functional value of high-standard terrace ecological service, can provide a theoretical basis for exploring the model of low input, high efficiency and sustainable agricultural development in loess hilly region. The study defined the ecological service function of high-standard terrace with opportunity cost method and shadow engineering method in Zhuanglang county. On the basis of soil fertility maintenance function, soil and water conservation function, and soil moisture conservation function, this paper built the model of material quality and value of ecological service function, and assessed ecological service function and value of high-standard terrace. The results showed:firstly, each hectare of high-standard terrace annually provided the total mass and value of ecological service for human beings respectively about 119 667.00 kg and 114 046.53 yuan, the value of ecological function was considerable. Secondly, soil erosion amount of sloping farmland and high-standard terrace was respectively 82.76 t/(hm²·a) and 0.05 t/(hm²·a), the amount of soil and water conservation of high-standard terrace was 82.71 t/(hm²·a), and the transformation of sloping farmland into high-standard terrace had a significant impact on the value of ecological service function. Thirdly, the value of soil and water conservation function of high-standard terrace unit area was 3 831.67 yuan/(hm²·a), far below the value of soil fertility maintenance function which was 88 869.52 yuan/(hm²·a) and the value of soil moisture conservation function which was 24 239.20 yuan/(hm²·a). There is still a lot of room for improvement and appreciation potential in the function of soil and water conservation in high-standard terrace, adjusting the industrial structure of terrace, selecting appropriate operation and development mode, improving the yield per unit area, and giving full play to the function of high-standard terrace. The construction of high-standard terrace has important features of production, ecology and living functions in the process of national economic development. The study provides a comprehensive evaluation method for the ecological function value accounting of high-standard terrace, and the results are helpful to improve the value accounting method of ecological function, maximize its ecological benefits, also excavate the potential ecological function and value, so as to realize the sustainable development of high-standard terrace ecosystem.

Abstract:In this paper, four different forest stands (larch pine forest, camphor pine forest, mixed forest of larch pine and camphor pine, and mixed forest of camphor pine and elm) of yudaokou pasture in weichang County, Chengde city were chosen as objects and their hydrologic effect of litter was studied by sample survey and indoor soaking method. The results showed that the amount of litter in various forest stands was 5.42~24.59 t/hm², of which larch pine forest had the largest amount, 24.59 t/hm², and the amount of mixed forests of camphor pine and elm was the smallest, 5.42 t/hm². The contents of the semi-partition layer of the four stands of forest were all larger than the undecomposed layer. The average maximum water holding capacity was larch pine forest (16.61 t/hm²) > mixed forest of larch pine and camphor pine (14.80 t/hm²) > camphor pine forest (10.22 t/hm²) > mixed forest of camphor pine and elm (9.99 t/hm²). The average maximum water holding rate was larch pine forest (427.02%) > mixed forest of camphor pine and elm (396.30%) > mixed forest of larch pine and camphor pine (360.88%) > camphor pine forest (303.13%). The effective retaining content was mixed forest of larch pine and camphor pine (74.65 t/hm²) > larch pine forest (71.21 t/hm²) > camphor pine forest (48.82 t/hm²) > mixed forest of camphor pine and elm (17.66 t/hm²). The effective retaining rate was larch pine forest (344.99%) > mixed forest of camphor pine and elm (326.66%) > mixed forest of larch pine and camphor pine (286.27%) > camphor pine forest (215.49%). The comprehensive results showed that larch pine forest has the best water holding capacity in litter layer, and the function of retaining water in litter layer of larch shelter forest in this area is better than other types of forest stand.

Abstract:The secondary forest formed by natural restoration after the large-scale logging of primary conifer forests has become one of the dominant forest types in a subalpine region of western Sichuan, and plays an important role in water conservation in the forests of southwestern China. However, less attention was paid to the water conservation function of subalpine natural secondary forest. Therefore, by using the method of replacing space with time, four typical vegetation types of shrub (dominated by Salix cupularis), broad-leavedforest (dominated by Betula spp.), mixed coniferous and broad-leaved forest (dominated by Abies faxoniana and Betula spp.), and old-growth conifer forest (dominated by A.faxoniana) along natural restoration with different stand ages in Miyaluo of western Sichuan were selected to measure soil bulk density, porosity and water holding capacity. The aim of this study was to quantify the changes of soil physical properties and water-holding capacity. The results indicated as follows:(1) The soil bulk density decreased with the vegetation restoration and increased with the depth, and the trend was subalpine conifer mature forest < mixed coniferous and broad-leaved forest < broad-leaved forest < shrub. (2) There were significant differences in soil porosity along natural restoration. The mixed coniferous and broad-leaved forest had the maximum total porosity (64.39%) and capillary porosity (50.49%) in the 0-30 cm soil layer, and shrub had the minimum total porosity (41.25%) and capillary porosity (33.70%). However, the soil non-capillary porosity was the highest in conifer forest (14.27%), and the soil porosity showed a decreasing trend with the soil depth. (3) The soil maximum water-holding capacity along the natural restoration varied nonlinearly with the increasing stand age, from 1 172.07 t/hm² for the shrub stage to 1 815.02 t/hm² for the mixed coniferous and broad-leaved forest, and to 1 659.88 t/hm² for the conifer forest. The mixed conifer and broad-leaved forest has the maximum soil capillary water holding capacity (1 369.72 t/hm²), while conifer forest has the maximum non-capillary water holding capacity (534.95 t/hm²), which indicated that the former needs more available water storage capacity for vegetation growth, and the latter has strong soil water regulation ability and permeability ability. It is concluded from this study that attention should be paid to the construction of conifer and broad-leaf mixed forest structure in the alpine forest restoration in western Sichuan for the improvement of water conservation function.

Abstract:In order to clarify the excessive consumption of deep soil moisture by vegetation and the carrying capacity of water resources in arid and water-deficient areas, the Robinia pseudoacacia plantation with a stand density of 1 300 trees/hm² was selected as the research object in the gully area of the Loess Plateau in Western Shanxi Province, and the bare land was taken as the control. The volumetric water content of soil layers in the 0-150 cm range and trunk sap flow of the local R. pseudoacacia plantation were continuously observed by using Enviro-SMART soil moisture location monitoring system and thermal diffusion probe (TDP). Using the ratio of available soil water to water consumption per plant of R. pseudoacacia to measure the carrying capacity of soil water and vegetation of R. pseudoacacia plantation in the study area. The results showed that:(1) Monthly precipitation and monthly soil water storage were the main environmental factors determining soil water and vegetation carrying capacity of R. pseudoacacia plantation, and there was a significant positive relationship between them and soil water and vegetation carrying capacity (P<0.05). (2) According to the soil water and vegetation carrying capacity model of R. pseudoacacia plantation, the soil water and vegetation carrying capacity of 0-150 cm soil layer depth of R. pseudoacacia plantation with 19 years of local age was calculated to be 1 224 plants/hm², slightly less than the actual stand density of the study area (1 300 plants/hm²). In order to ensure that the water consumption depth of the local R. pseudoacacia plantation is controlled within the 0-150 cm soil layer, and to promote the productivity of the local stand at the optimal level, it is suggested that the density of the plantation should be controlled within the carrying capacity of the local soil moisture and vegetation in the future afforestation process, so as to reduce the deep water consumption of the forest land and adjust the balance of soil water resources in the forest land, and promote the rational development of local forestry industry.

Abstract:Under the rainfall from June to October, 2018, the standard runoff plots in garden land, forest land, grassland, farmland and bare land were taken as research object, with the bare land as the control. The soil moisture contents, total nitrogen, nitrate nitrogen and ammonium nitrogen contents in different soil depth and time were studied in garden land, forest land, grass land, farmland and bare land. Through statistical analysis of field test data, the effects of rainfall on soil water and nitrogen change characteristics under different land uses were proposed. The results showed that the rainfall increased soil moisture content in garden land, forest land, grassland, farmland and bare land and accelerated soil total nitrogen, nitrate nitrogen and ammonium nitrogen hydrolysis conversion of nitrification and denitrification rate, affected the soil moisture contents, total nitrogen, nitrate nitrogen and ammonium nitrogen contents. The rainfall had significant correlations (P<0.05) with soil moisture contents, total nitrogen, nitrate nitrogen, ammonium nitrogen. Under rainfall, soil moisture content increased with the soil depth in garden land, forest land, grassland, farmland and bare land. At soil depth of 100 cm, soil moisture content was the largest, which were 30.34%, 27.67%, 24.98%, 24.03% and 21.95%, respectively. Total nitrogen contents increased first and decreased then with the increasing soil depth, and at the soil depth of 60 cm, soil total nitrogen was the largest, which were 1.02, 0.99, 0.90, 0.86 and 0.75 g/kg, respectively. Nitrate nitrogen and ammonium nitrogen contents decreased with the increasing soil depth. The nitrate nitrogen and ammonium nitrogen contents at soil depth of 100 cm were the smallest, among which the nitrate nitrogen was 9.01, 7.89, 7.25, 6.10, 5.22 mg/kg, and the ammonium nitrogen was 9.41, 9.14, 6.40, 5.38, 4.37 mg/kg, respectively. With the time, soil moisture contents decreased first, then increased, and then decreased at last, showing a positively cosine changing trend. Soil moisture contents was the largest in August, which were 22.97%, 22.01%, 19.87%, 19.03% and 17.98% respectively. Total nitrogen first increased and then decreased with time, with the largest in August, which were 1.09, 1.01, 0.94, 0.84 and 0.76 g/kg, respectively. Nitrate nitrogen and ammonium nitrogen contents reduced gradually with time. Soil nitrate nitrogen and ammonium nitrogen contents were larger in June. Soil nitrate contents were 13.40, 12.37, 11.20, 10.39, 8.67 mg/kg, ammonium nitrogen 18.89, 17.02, 14.54, 12.02, 8.36 mg/kg, respectively. The relationships between average soil moisture contents, total nitrogen, nitrate nitrogen and ammonium nitrogen contents and soil depth and time in different land uses were following as:garden > woodland > grassland > sloping land > bare land. This study could provide theoretical and technical support for soil water and fertilizer loss control and nutrient utilization in farmland.

Abstract:The effects of lignin and biochar addition on soil nitrogen (N) and phosphorus (P) nutrients and water loss were researched in order to reduce the cost of soil amendment, increase the utilization of lignin that came from papermaking black liquor, and promote the application of lignin in soil amendments. The biochar amendment and lignin were selected as the comparison in this study. The effects of lignin and biochar with different additions (0, 1%, 2%, and 4% respectively in the mass fraction) on N, P, water loss, urease activity and pH value in soil were studied by the soil column simulation method and static absorption method. Both addition of lignin and biochar in soil could alleviate the changes of pH value and could inhibite the activity of urease. The inhibition effect was obvious after adding N fertilizer 1~20 days when the inhibition rate was positively correlated with the addition amount. Compared with the CK, the amount of lignin and biochar added with 1%, 2% and 4% could significantly reduce the volatilizing amount of ammonium N by 8.29%, 14.29%, 14.86% and 3.79%, 11.65%, 15.26%, respectively. Total N leaching amount was significantly reduced by 32.37%, 37.70%, 42.49% and 25.43%, 30.70%, 39.54%, respectively. Total P leaching amount was significantly reduced by 23.68%, 40.48%, 48.12% and 6.97%, 22.88%, 35.30%, respectively. The water loss was significantly reduced by 7.71%, 15.82%, 9.29% and 9.91%, 15.00%, 16.06%, respectively. In this experiment, the best mass fraction of lignin and biochar was 2% and 4% respectively when the inhibition effect on soil N, P nutrients and water loss was the best. Therefore, it could be found that lignin could replace biochar amendment in soil to some extent for the similar function of water and fertilizer conservation and similar effect on inhibiting urease activity to biochar.

Abstract:In this study, the water flow of red soils in upland field, paddy field, and forest in Yingtan city were studied by the dye tracing experiment and digital image analysis. The parameters of dye distribution characteristics in three fields were quantified and their water flow patterns were defined. The effects of soil physiochemical properties on the water flow patterns were revealed. The results showed that the staining area ratio (SAR) decreased sharply with increasing soil depth. The higher average SAR of 0-60 cm soil layer was observed in paddy field (28.16%) than that in upland field (21.95%), and forest (18.64%), and these differences in SAR mainly happened in 5-25 cm soil layer. The staining path number (SPN) in three fields increased from soil surface to 15 cm soil depth, and then decreased continuously along the soil profile. The highest average SPN of 0-60 cm soil profile was observed in paddy field (20), followed by upland field (12) and forest (9). The soil layer of 0-20 cm depth in three fields were mainly occupied by the type of 1-10 cm staining path width (SPW), and their water flow patterns were defined as the homogeneous matrix flow, heterogeneous matrix flow, and high interaction macropore flow successively along the soil profile. For the soil layers underneath 20 cm, the upland field and forest were mainly occupied with SPW of<1 cm and water flow pattern of low interaction macropore flow and mixed interaction macropore flow. However, the SPW of 1-10 cm and the water flow pattern of high interaction macropore flow were mainly defined for the forest soil below 20 cm depth. The soil saturated water conductivity and water flow characteristics in three fields were strongly depended on the soil pore characteristic, which was mainly affected by the organic matter content, root density and soil particle size. In order to improve the water use efficiency and reduce soil erosion in the red soil area, the methods of breaking the plough pan of upland field, reducing soil crack formation in paddy field by rational irrigation management, and increasing the vegetation diversity of forest would be efficient.

Abstract:In the arid and semi-arid regions of northwestern China, Lycium barbarum production is facing the problems of single planting pattern and low water use efficiency. The purpose of this study was to explore more effective field management measures to increase L. barbarum production and achieve efficient utilization of land and water resources. Based on field experiments, the effects of two planting patterns and four water conditions on water consumption characteristics, photosynthetic characteristics, growth, yield, and water use efficiency of L. barbarum were compared and analyzed. The two planting patterns were L. barbarum monoculture (CK) and intercropping of L. barbarum and Alfalfa (LA). The four kinds of water condition were full irrigation (W0, 75%~85%), mild water deficit (W1, 65%~75%), moderate water deficit (W2, 55%~65%), and severe water deficit (W3, 45%~55%). The results showed that:(1) The water consumption during the growth period of LA (891~1 243 mm) was higher than that of CK (829~1 102 mm), and decreased with the increasing of water deficit. (2) In CK, the double peak trends of net photosynthetic rate and transpiration rate were more obvious than those of LA. Additionally, under the same planting mode, the peaks of net photosynthetic rate and transpiration rate of L. barbarum leaves decreased and the peaks appeared earlier with the aggravation of water deficit. (3) Under the same planting mode, the growth amount of L. barbarum ground diameter, plant height, crown width and new shoots decreased with the aggravation of water deficit, but the decreasing range tended to decrease. In the single planting mode, the treatment of CKW1 had higher yield (3 720 kg/hm²) and water use efficiency (3.61 kg/(hm²·mm)). In the intercropping mode, the treatment of LAW0 had higher yield (3 780 kg/hm²) and water use efficiency (3.08 kg/(hm²·mm)). In conclusion, a certain degree of water deficit was helpful to improve the yield and water use efficiency of L. barbarum in the single planting mode, and sufficient soil water supply should be ensured to obtain higher L. barbarum yield and water use efficiency in the intercropping mode.

Abstract:To study the effects of forest and grass vegetation restoration on soil aggregate size distribution, soil structure stability, and aggregate soil organic carbon in rocky desertification control area of karst plateau, in order to provide theoretical basis for improving soil structure, revegetation, maintaining, and improving soil organic carbon pool, five common forest and grass vegetation (honeysuckle, pitaya, Zanthoxylum bungeanum, wild ground grass, and native shrubbery) in the demonstration area of rocky desertification control in the Karst Plateau of Guizhou were taken as the research object, soil aggregate grain diameter were grouped by wet sieving method, the distribute of aggregates and soil organic carbon content in each soil layer in the vertical profile of 0-40 cm soil layer under five forest and grass vegetation modes was comparatively analyzed. The results showed that in the vertical profile of 0-40 cm soil layer, the distribute characteristic of the soil aggregates in four grain sizes of >5, 2~5, 0.25~2, and <0.25 mm were shown as:honeysuckles 31.89%, 32.85%, 28.48%, 6.78%; pitaya 19.11%, 32.68%, 37.72%, 8.49%; Z. bungeanum 10.42%, 18.39%, 57.90%, 13.29%; wild ground grass 40.38%, 20.68%, 30.34%, 8.61%; native shrubbery 47.04%, 17.80%, 30.25%, 4.91%. The water-stable macro aggregate content (>0.25 mm) showed as native shrubbery (95.09%) > honeysuckle (93.22%) > pitaya (91.51%) > wild ground grass (91.39%) > Z. bungeanum (86.71%). In general, aggregates in the five forest and grass vegetation were dominated by macro aggregates (>0.25 mm); among them, soil from the native shrubbery had the highest content and soil from the Z. bungeanum had the lowest content. In the whole soil profile, the soil aggregate stability indicators MWD and GMD of the native shrubbery were higher, which indicated that the soil structure is better and the stability is stronger. In the 0-40 cm soil profile, the organic carbon of each aggregate level decreased with the increase of soil depth, and showed surface layer enrichment. The organic carbon of aggregate showed the highest content in<0.25 mm level, and the lowest content in >5 mm level. Generally speaking, the soil aggregates of native shrubbery land had a better stability, and had the highest content of organic carbon in each layer of each aggregate level.

Abstract:In this study, different types of pisha sandstone in Zhungeer Banner, Ordos, Inner Mongolia were selected to study the characteristics of organic matter (OM) and available potassium (AK) in soil through field sampling and indoor experiments, and the impact of different soil layers, slope position and slope direction, vegetation richness and other factors on OM and AK was also explored. The results showed that:(1) On the whole, the content of OM in the loess covered area, the sand covered area and the exposed area was between 6.65~7.41 g/kg, which was at a low level, and the content of AK was between 74.61~137.38 mg/kg, which was at a medium high level. (2) Topographic factors had the most obvious effect on soil OM and AK in the loess covered area. Slope direction, slope position and the interaction between slope direction and slope position were correlated with soil nutrients, according to the frequency of significant or extremely significant occurrence. The relationship of the degree of influence was preliminarily demonstrated as slope position > slope direction > slope direction×slope position. (3) There was a high correlation between vegetation richness and soil OM and AK content in three different types of regions, which is an important factor to be considered in soil nutrient study.

Abstract:In order to investigate the effects of biochar application on soil aggregates stability, organic carbon, and total nitrogen distribution, further elucidate the long-term effective mechanism of biochar addition on farmland in the hilly area of western Henan Province, China, a 5-years field experiment was conducted to explore the effects of biochar application(0 (C0), 20 (C20), 40 (C40) t/hm²) on soil aggregates composition and stability, and illustrated the distribution characteristics of organic carbon and total nitrogen in soil aggregates. The results showed that biochar application with 20 and 40 t/hm² increased the contents of > 0.5 mm mechanical and > 0.053 mm water stable aggregates. In the 0-20 cm soil layer, compared with the control, C20 and C40 treatments increased the >0.25 mm mechanical aggregate (DR_0.25) by 3.78% and 6.83%, increased >0.25 mm aggregate water stability (WR_0.25) by 31.0% and 49.45%, decreased unstable soil aggregate index (E_LT) by 4.30% and 6.85%, decreased proportion of soil aggregate destruction (PAD) by 9.71% and 14.77%, increased the mean weight diameter (MWD) of soil aggregates by 28.44% and 45.34%, and increased the geometric mean diameter (GMD) significantly by 32.04% and 54.92%. The content of organic carbon and total nitrogen increased with the increase of biochar application rates in each size fraction, was the highest in 0.25~0.053 mm aggregate. The contents of organic carbon and total nitrogen in 0-20 cm soil layer was higher than that in the 20-40 cm soil layer. With the increase of biochar application amounts, the contribution rates of organic carbon and total nitrogen increased at >2, 2~0.25 and 0.25~0.053 mm aggregates, and the contribution rates of organic carbon and total nitrogen decreased at <0.053 mm aggregate. In general, biochar improved the soil aggregate structure, increased the content and stability of soil macro-aggregate, and increased the contents of organic carbon and total nitrogen in each size fraction, which was beneficial to maintain the soil fertility and the long-term healthy development of farmland in the hilly area of western Henan Province.

Abstract:To identify the adaptation strategies of plants in semi-arid areas to periodical changes of water and nutrient supply, a pot experiment was conducted to investigate plant growth, root morphological characteristics, N and P concentration under two soil moisture conditions (well-watered and post-drought rehydration) and two phosphorus (P) addition levels (0 and 0.2 g P₂O₅ per kg dry soil) of Old World bluestems at its jointing stage. Results showed that under re-watering after drought, effect of P addition on shoot and root biomass, total biomass, and root/shoot ratio of Old World bluestems have no significant difference, while total root length and root surface area increase 27.1% and 24.1%, specific root length and specific root area increase 18.3% and 15.9%, and root average diameter decrease 1.3%. P concentration in shoot, root and whole plant of Old World bluestems significantly increased 61.1%, 35.8% and 49.6%, respectively, and P accumulation significantly increased 68.6%, 52.0% and 61.3%, respectively, and, N:P ratio decreased significantly. In addition to N accumulation in shoot, N and P accumulation in shoot, root, and whole plant of Old World bluestems under different water and phosphorus treatments showed significant positive correlation with total root length and root surface area. The present study suggested that increases in root length and root surface area were the main adaptation strategies of Old World bluestems in response to periodical changes of water supply and phosphorus addition.

Abstract:The effects of incorpotation of reduced chemical fertilizer combined with Chinese Milk Vetch (Astragalus sinicus L.) on rice yield and nitrogen use efficiency was studied in subtropical double-rice cropping system. The experiment was carried out in a double-rice cropping system, and ten different treatments (two levels of reduced chemical fertilizer combined with four different amounts of Chinese milk vetch) were set to investigate the effects of different combination on the yields and nutrient use efficiencies of early- and late-rice. The results indicated that early-rice yields of all treatments which applied with 15 000~37 500 kg/hm² Chinese milk vetch and 80% recommend chemical fertilizer showed significant increasing, and was 5.0%~13.2% higher than that of recommended fertilizer treatment (100%F). The early-rice yields of treatments which applied with 15 000~22 500 kg/hm² Chinese milk vetch and 60% recommend chemical fertilizer showed no significant differences with that of the 100%F treatment, while the early-rice yields of treatments applied with 30 000~37 500 kg/hm² Chinese milk vetch and 60% recommend chemical fertilizer were 5.4%~8.5% higher than that of 100%F (P<0.05). Agronomic efficiency, partial factor productivity and recovery efficiency of applied chemical fertilizer N of all treatments with Chinese milk vetch applied were all significantly higher than that of 100%F in early-rice season, but no significant differences were found in late-rice season. When nitrogen derived from Chinese milk vetch application was counted into the total nitrogen input, agronomic efficiency of applied N of all treatments with Chinese milk vetch application showed declining trends as the Chinese milk vetch increasing in early-rice season. Compared with 100%F, agronomic efficiency of applied N of all treatments with Chinese milk vetch application showed no significant differences, but N recovery efficiency was significantly decreased when the Chinese milk vetch application was 37 500 kg/hm² and above. Soil total nitrogen content of all treatments with Chinese milk vetch application was higher than that of 100%F, but the differences were not significant (P>0.05). However, the differences of soil available nitrogen content between 100%F and all treatments with Chinese milk vetch application were significant (P<0.05). Long-term application of Chinese milk vetch combined with chemical fertilizer showed positive effects on yields and nitrogen use efficiency in both early- and late-rice seasons in subtropical double-rice cropping system. Continuous application of Chinese milk vetch was conducive for soil organic matter and total nitrogen content, and its impact on soil available nitrogen content improvement was significant. Therefore, the combination ratio of Chinese milk vetch and chemical fertilizer not only can reduce chemical fertilizer application, but also is an effective technique to improve rice yield and soil fertility in double-cropping paddy field. Based on the experiment results and experimental area condition, 60% recommend chemical fertilizer +22 500~30 000 kg/hm² Chinese milk vetch is appropriate.

Abstract:Field experiments were conducted to study the effects of synergetic addition in the fertilizers such as polyaspartic acid, humic acid, and nitrification inhibitor DMPP (3,4-dimethyl pyrazophosphate) on the nitrogen transformation of rice surface water and rice yield by planting single cropping rice "shaojing 18" in paddy field. The results showed that the total soluble nitrogen, ammonium nitrogen and nitrate nitrogen concentrations in the rice surface water were significantly increased by fertilization. With the application of synergists such as polyaspartic acid, DMPP, humic acid and so on, the average soluble total nitrogen concentration in the rice surface water decreased by 14.1%, 15.8%, and 7.3%, ammonium nitrogen increased by 10.6%, 27.5%, and 8.6%, and nitrate nitrogen declined by 31.8%, 46.7%, and 26.9%, respectively, which helped to reduce the risk of non-point source pollution caused by the nitrogen runoff loss to water environment. Polyaspartic acid, DMPP, and humic acid application increased rice grain yield by 6.2%, 7.8%, and 2.4%, and increased straw yield by 10.8%, 6.1%, and 4.0% respectively. Compared with common fertilizers, synergist addition in the fertilizers can reduce the total nitrogen content in the rice surface water, and better promote the growth of rice and increase the yield.

Abstract:In order to explore the suitable water content of different salt soils of slfalfa in the Hetao Irrigation District, a pot experiment was carried out. Three water levels, three salt levels and one control (CK) are set up to monitor the changes of soil water storage, quality and yield of alfalfa from the bud stage to the initial flowering stage. The results showed that:(1) Plant height, aboveground biomass, underground biomass, water consumption and hay yield increased with the increase of water under the same salt conditions. But with the increase of irrigation amount, the increasing effect of irrigation on the yield of alfalfa was significantly reduced. Under the same water condition, the water consumption and the underground biomass increased with the increase of salt and then decreased. If the soil salinity was more than 3 g/kg, the water storage in the soil increased significantly, and gradually increased with the increasing irrigation amount. (2) When the soil salt content was 1~3 g/kg, water stress was beneficial to increase the content of crude protein. The content of crude protein in low water treatment was significantly higher than that in middle water and high water treatment (p<0.05). When the salt content was 3~4 g/kg, the soil salt changed the water stress threshold. The crude protein content of the treated water was significantly higher than that of the low water and high water treatment (p<0.05). Under the salt and water stress, the amino acid content of the plant increased, and the F₃W₁ treated amino acid content was the largest, which was 20.90%. Under the same salt condition, the amino acid content decreased stepwise with the increase of water content. Correlation analysis of each free amino acid and crude protein content showed that the correlation between glycine and methionine was not significant, but the correlation between other amino acids and crude protein was positively correlated (p<0.05). (3) When the soil salinity was in the range of 1~2 g/kg, and the water use efficiency of the water was decreasing. But when the soil salinity exceeded 2 g/kg, and the water use efficiency increased first and then decreased with the inceasing irrigation amount. When the soil salinity was 1~2 g/kg, and the water content was 70%θ_f~75%θ_f, both the yield of hay and water use efficiency were increased. When the soil salinity was 2~3 g/kg, the water content was 70%θ_f~85%θ_f, the water use efficiency was improved, the hay yield was decreased, but it is not significant. When the soil salt content was 3~4 g/kg, and the water content was above 85%θ_f, alfalfa production was increased. The results of this study could provide a theoretical basis for the cultivation and rational irrigation of salinized farmland.

Abstract:Saline-alkali stress is one of the significant abiotic stresses affecting plant growth worldwide. However, the adaptive capacity and physiological response mechanism of Xanthoceras sorbifolia to saline-alkali stress are still poorly understood. In this study, 1-year-old Xanthoceras sorbifolia seedlings were used. We aimed to explore the adaptability of the seedlings to saline-alkali stress, and to reveal the physiological response of hydraulic structure and carbon metabolism of the seedlings to different salinity-alkali stresses. The results showed that:(1) Saline-alkali stress significantly reduced survival rate, plant height, basal diameter, biomass of different parts, predawn water potential, root hydraulic conductivity, photosynthetic rate and stomatal conductance of the seedlings. (2) Along with the increase of saline-alkali stress degree, the contents of NSC in roots, stems and leaves increased first and then decreased. Moreover, the damage degree of saline-alkali stress was significantly higher than that of neutral salt, mirrored as lower survival rate, smaller biomass, lower water potential, root hydraulic conductivity and photosynthetic rate. (3) Saline-alkali stress limited the water absorption ability of root system, and affected the water status of plants, then influenced plant growth and NSC accumulation, even plant survival. The effect of saline-alkali stress was more severe than that of neutral salt. (4) Xanthoceras sorbifolia could adapt to mild saline-alkali environment, while moderate and severe saline-alkali stress would have a great influence on its growth and survival. The physiological response of the seedlings to different types and degrees of saline-alkali stress in terms of water structure and carbon metabolism could provide a basis for the site selection, cultivation range expansion and large-scale development of the Xanthoceras sorbifolia.

Abstract:Indoor soil column simulation was used to study the improvement effect of saline soil under different irrigation volumes. The three different irrigation volumes in the experimental design were S1 (200 mm), S2 (300 mm), and S3 (400 mm). The results showed that:(1) Irrigation had a great influence on the leaching of soil salinity in 0-40 cm soil layer. Soil layer in 0-20 cm had the highest desalination rate, which performance was S3 > S2 > S1. Salt accumulation occurred in the profile of different irrigation volumes, and was observed in the 40-60 cm soil layer of S1 and S2, which indicated that low amount irrigation had leaching effect on the surface soil salt, but could cause salt accumulation in the bottom soil. (2) The contents of K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, and HCO₃^- decreased after irrigation, and the overall dissolution rate of salt ion increased with the increase of irrigation volumes. The variation of each ion showed different changes with the increase of irrigation volumes in 0-20 cm soil layer. Ca²⁺ firstly accumulated and then dissoluted, while HCO₃^- dissoluted firstly and then accumulated, and the other ions decreased with the increase of irrigation volumes. (3) After irrigation, the distribution of S1 and S2 pH in profile was similar to that before irrigation. The total alkalinity of 0-40 cm soil layer increased firstly and then decreased with the increase of irrigation amount, which was firstly alkalized and then alkali removed, and was consistent with the change of pH. The research results can provide reference for water-salt balance and water-saving irrigation in saline-alkali soil.

Abstract:Aiming at the salinity stress problems in rice root growth in the paddy soil of coastal saline-alkali soil, and the consequent low nutrients use efficiency, afield experiment was conducted to study the effects of combined application of organic and phosphate fertilizers on root growth in different growth stages, yield and nutrients use efficiency of rice in coastal saline soil. The experiment had two factors, including three carbon levels:(1) C0, no carbon; (2) C1:low carbon, 450 kg/hm²; (3) C2:high carbon, 900 kg/hm², and three phosphate fertilization (P) levels:(1) P0:no P; (2) P1:low P, P₂O₅64 kg/hm²; (3) P2:high P, P₂O₅128 kg/hm².Results showed that the total root surface area of T5 treated with low carbon and low P was significantly higher than those of high carbon and low phosphorus treatments (T7) and high carbon and high phosphorus treatments (T8), which increased by 25.2% and 30.2%, respectively. The total root volumes of low carbon treatments (T5, T6) were significantly higher than that of high carbon treatment in the harvest stage of rice. The rice yield and biomass of T5 were 10 245 and 9 550 kg/hm², respectively, and higher than others treatments. High seed setting rate was the reason for the highest yield of rice treated with low carbon and low P (T5) treatment. P accumulation of rice in low carbon and low P (T5) treatment was significantly higher than those in T6, T7 and T8 treatments, which were higher than 13.9%, 27.8% and 31.2%, respectively. The fertilizer contribution rate (FCR) and agronomic efficiency (AE) of P fertilizer under T5 treatment were significantly higher than others treatments. The partial fertilizer productivity (PFP) P fertilizer was significantly higher at low P input than that of high P input. In conclusion, compared with only inorganic fertilizer, combined application of organic fertilizer with P fertilizer could significantly promote rice root growth, increase rice yield and agronomic efficiency of P fertilizer in coastal saline soil. Low carbon and low P (T5, C450 kg/hm² and P₂O₅ 64 kg/hm²) treatment was the most favorable for rice root growth in coastal saline soil.

Abstract:Taking the subtropical pine plantation as research object, the soil biochemical properties and enzymes activities were studied using three simulated sulfur deposition experiments with different levels (control treatment, CK:pH 6.5; low sulfur treatment, LS:pH 4.5; high sulfur treatment, HS:pH 2.5). The results showed that:(1) Sulfur input had a significant effect on soil acid, HS significantly reduced the 0-5 cm soil pH, both LS and HS treatments could significantly reduced the 5-10 cm soil pH (P<0.05). (2) Sulfur input had a certain effect on soil organic carbon pool. Soil total organic carbon (TOC) had no significant response to sulfur input, but its differences increased in soil layers (P<0.05). The impact of sulfur input on soil dissolved organic carbon (DOC) was limited. HS significantly decreased soil microbial biomass carbon (MBC) from 5-10 cm soil layer and increased the differences in soil layers (P<0.05). (3) Sulfur input had different effect on soil effective nitrogen pool. Soil dissolved organic nitrogen (DON) and ammonium nitrogen (NH₄⁺-N) had no significant change. HS treatments significantly decreased soil nitrate nitrogen (NO₃^--N) and soil microbial biomass nitrogen (MBN) and increased the differences in soil layers (P<0.05). (4) Sulfur input inhibited the activity of soil enzyme. HS significantly decreased soil urease activity (P<0.05). Soil invertase activity had no significant changes, but sulfur input reduced the differences of enzymes activities in the two soil layers. The comprehensive analysis of soil biochemical characteristic and enzymes activities indicators from all treatments showed that soil pH and enzymes had sensitive responses to sulfur input. Soil layer was another major impact factor. But the interaction between sulfur addition and soil layer had the limited impact. Through the Pearson method, sulfur input changed the correlation of the soil biochemical properties and enzymes activities. The effect of simulated acid rain on soil acidification was a gradual process of accumulation. The effect of exogenous sulfur addition on soil carbon, nitrogen and enzymes activities was different. The results could provide scientific basis for forest management under environmental stress of sulfur deposition.

Abstract:The adsorption and desorption of ammonium by biochar affects the nitrogen fixation effect of soil. To explore the effect of tea residue biochar on the adsorption-desorption of NH₄⁺-N in tea garden soil, reduce nitrogen leaching in soil, and improve nitrogen use efficiency, through a simulated culture experiment, the equilibrium adsorption method and HCL desorption method were used to study the adsorption-desorption of NH₄⁺-N characteristics in tea garden soil in which the biochar that prepared at different pyrolysis temperatures was differently added (0.35%, 0.70%, 1.40%, 2.80%). The results showed that the application of biochar could effectively enhance the adsorption of NH₄⁺-N by tea garden soil and the enhancement increase with the increase of biochar addition. Under the same addition, the adsorption amount of NH₄⁺-N in the tea garden soil treated by four kinds of biochar trended as BC400 > BC300 > BC500 > BC600. The CEC content of biomass carbon was the main factor affecting the ability of soil to adsorb NH₄⁺-N. The adsorption process of NH₄⁺-N by soil, which was dominated by monolayer adsorption, reached a significant level by matching the Langmuir equation (0.953 7<R²<0.995 5). After the application of biomass charcoal, the soil produced a known absorption hysteresis, which effectively reduced the desorption rate of NH₄⁺-N in tea garden soil, and the desorption rate of BC400 was the lowest. Tea residue biochar can enhance the adsorption of NH₄⁺-N in soil, reduce the desorption of NH₄⁺-N, improve the ability of soil to absorb nitrogen, and the treatment of BC400 with 2.80% addition showed the best effect.

Abstract:Urban rivers pollution is a serious issue facing the world today. With the controlling progressively for most of the urban point source pollution, endogenous release of nitrogen and phosphorus from sediments, which could continuously pollute river water, became the greatest challenge for the remediation of urban river. The purpose of this study was to examine the spatial and temporal characteristics and risks of nitrogen forms in surface sediments of the river with basin rapid urbanization. Liangtan River, which is a typical urban river and has been greatly polluted due to the rapid development of the city and industry on the basin of wastewater, was selected to carry out a seasonal investigation of nitrogen forms and water environment parameters. The results showed that the range of total nitrogen (TN) concentrations in surface sediment of Liangtan River and its tributary (Huxi River) were 2.63~8.12 g/kg, and contents of the ion exchange nitrogen focusing (IEF-N), weak acid leaching nitrogen (WAEF-N), alkali leaching (SAEF-N) and strong oxidant may leach nitrogen (SOEF-N) contents were 190~1 764, 119~1 139, 208~2 039 and 159~2 829 mg/kg, respectively. The high variability of such N forms was attributed to the distribution pattern of the pollution sources (such as urban, industry, and farming) in the basin. The contents of TN, WAEF-N, SAEF-N and SOEF-N in sediments decreased gradually from the upstream to the downstream of Liangtan River, while the IEF-N with the highest activity showed different peaks in the urban reach, indicated that the spatial distribution of the N forms in river sediments was dominated by the watershed anthropogenic activities and pollution types. Meanwhile, the transferable nitrogen (TF-N) accounted for 52.9%~72.3% in TN, with higher IEF-N percentage in urban reach than these in non-urban reach, showing the higher release risk of N in urban river. Seasonal pattern of the majority N forms in surface sediment of Liangtan River showed the winter were significantly higher than summer. The statistical analysis showed that sediment different N forms parameters had significant correlations with each other, indicating that their closely mutual transformation connection; in addition, the contents of different N forms were significantly and positively associated with pH, DO, and DOC in surface water, indicating that exogenous water pollution hand a positive impact on sediment nitrogen release. Overview, N forms in the surface sediment of Liangtan River showed a great variability in spatial as the results of the pollution sources pattern in the process of urban development. There was a high release risk in the urban reaches due to the small molecular carbon input and higher exogenous pollution loading. The regulation of endogenous nitrogen release was the key point for river management in the future.

Abstract:In order to explore the pollution of Mercury (Hg) in surface dust of different micro-environment in driving schools in Wuhu City, the concentrations of Hg in 26 driving schools with full and fine particle sizes were measured by Hydra II C, and the statistical analysis was carried out. The results showed that the average concentrations of Hg in the full and fine particle sizes dust on the surface of driving school were 49.36 ng/g and 59.97 ng/g, respectively, which were lower than the background value of soil in Wuhu City, and there were statistically significant differences in Hg concentrations between the full particle size and the fine particle size. For the full particle size dust, the average concentrations of Hg in different training programs of driving school were in decreasing order of reverse stall parking > S bending > side parking > right angle turning > parking on ramps, and the fine particle size dust showed as follows:reverse stall parking > S bending > side parking > parking on ramps > right angle turning. Both of them showed a similar regularity. The Hg content of fine particle size dust in the three items of reverse stall parking, S bending and side parking were significantly higher than that in the right angle turning and the parking on ramps, the Hg content of full particle size dust in the reverse stall parking was significantly higher than that in the parking on ramps. Through the analysis of the factors affecting the dust Hg of driving school surface, it was found that the average concentration of Hg in indoor driving school was higher than that of outdoor driving school, the concentration of Hg in gas driving school was significantly higher than that in fuel driving school, and there were significant difference in Hg concentrations of surface dust between fuel and gas driving schools. It was found that the concentrations of Hg in S bending, reverse stall parking and side parking were significantly correlated with coach vehicle density, and the Hg concentration of surface dust in Wuhu driving school was affected by vehicle exhaust emissions. Hg pollution caused by vehicle exhaust emissions, fuel leakage and tire wear could not be underestimated, and there was an accumulation phenomenon. The coaches' health was threatened, as they were working in driving school all the year round. The Hg pollution in driving school should be taken seriously.

Abstract:In order to clarify the ecological stoichiometric characteristics of soil carbon (C), nitrogen (N) and phosphorus (P) in different land-use types (paddy field, vegetable field and jasmine garden) of Fuzhou farmland, the contents of total carbon (TC), total nitrogen (TN) and total phosphorus (TP) and their ecological stoichiometric characteristics were measured and analyzed. The results showed that the averaged TC content in soil was:paddy field > vegetable field > jasmine garden (P<0.05). In spring and autumn, the averaged TN content in soil was:paddy field > vegetable field > jasmine garden (P<0.05). However, in summer and winter, the averaged TN content in soil was:vegetable field > paddy field > jasmine garden (P<0.05). In each season, the averaged content of TP in vegetable soils was the largest (P<0.05), and in winter, the averaged content of TP in vegetable soils appeared the maximum (P<0.05). The C/N value, C/P value and N/P value of soil were between (10.17~12.89), (0.46~0.86) and (4.76~9.61) respectively in different land types. The seasonal difference of C/N value was not significant, except in summer, which was slightly higher than that of other seasons. It is worth mentioning that the C/N value of vegetable soil was lower than that of paddy field and jasmine garden in each season (P<0.05). C/P value and N/P value had no significant seasonal difference in the whole year, which showed:paddy field > vegetable field > jasmine garden (P<0.05). The C and N storage of vegetable soil were higher than those of paddy soil and jasmine garden soil in each season (P<0.05). There was no significant difference in C and N storage between paddy soil and jasmine garden soil in each season, but the C and N storage of different soil types in autumn were lower than those of other seasons (P<0.05). Overall, compared with other soils, the content of C, N and P in jasmine garden soil were the lowest, while the content and storage of N and P in vegetable soil were higher. What's more, the ecological stoichiometric characteristics of soil carbon, nitrogen and phosphorus were obviously different in those three land-use types, and it can be used to indicate the fixation of carbon, nitrogen and phosphorus in soil and the limited nutrient of soil.

Abstract:Reducing the accumulation of cadmium in the rice grain is the important target of heavy metal pollution control in China. In this study, a field experiment was conducted in a moderate heavy metal contaminated farmland to study the combined effects of applying amendments and water management on reduction of cadmium uptake of rice plant from soil. The field experiment included eight treatments, i.e., no amendment + shallow irrigation (control), biochar + shallow irrigation, calcium magnesium phosphate-palygorskite-sulfur powder (100:50:1) + shallow irrigation, limestone-zeolite-sulfur powder (100:50:1) + shallow irrigation, no amendment + deep irrigation, biochar + deep irrigation, calcium magnesium phosphate-palygorskite-sulfur powder + deep irrigation, and limestone-zeolite-sulfur powder + deep irrigation. Total dosage of all various amendments was 3 t/hm². The results showed that the uptake of cadmium by rice plant from soil was reduced significantly by the application of amendments and deep irrigation. Combined effects of both amendments and deep irrigation were greater than those of amendments or deep irrigation. Compared with the control, the contents of cadmium in the grain for treatments of calcium magnesium phosphate-palygorskite-sulfur powder + deep irrigation and limestone-zeolite-sulfur powder + deep irrigation were reduced by 56.53% and 55.53%, respectively. Effect of biochar on reducing the uptake of cadmium was relatively small. The application of the compound amendments could convert the exchangeable cadmium in the soil into relative stable form of cadmium such as carbonate bound, oxide bound and residual forms, and thus reduce the bioavailability of cadmium in soil and the uptake of cadmium from soil. Deep irrigation could enhance the soil reduction and the formation of cadmium sulfide, and achieved the purpose of reducing the uptake of cadmium from soil by dilution effect. The result suggested that application of amendments combined with deep irrigation was a convenient and effective technique to control cadmium uptake of rice plant from soil.

Abstract:Through a pot soil-culture experiment in greenhouse, the effects of exogenous H₂O₂ treatment with different concentrations (0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.3 mmol/L) on the growth, photosynthetic system, and fluorescence characteristics of Z. jujube seedlings under the stress of 0.05 mmol/L Cd were studied. The results showed that:(1) Under Cd stress, the growth of Z. jujube seedlings was inhibited. After H₂O₂ treatment, the Cd resistance coefficient, photosynthetic chlorophyll content, net photosynthetic rate (P_n), transpiration rate (T_r), and stomatal conductance (G_s) of Z. jujube seedlings increased, while H₂O₂, malondialdehyde (MDA) content, and intercellular CO₂ concentration (C_i) decreased with different degrees. (2) The activities of antioxidases (Peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT)) in the leaves and roots of Z. jujube enhanced after treatment with low concentration of H₂O₂ (≤ 0.08 mmol/L), and the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), sedoheptulose-1,1-bisphosphatase (SBPase), and fructose 1,6-diphosphate aldolase (SBPase) in the leaves increased significantly by 38.24%, 42.15%, and 84.08%, respectively. However, there was no significant change for the activity of transketolase (TKase). (3) The maximal photochemistry efficiency (F_v/F_m), actual photochemistry efficiency (ΦPSⅡ), photochemical quenching coefficient (qP), and the share of absorbed light energy for photochemical reactions (P) in the leaves of Z. jujube increased by 37.52%, 135.95%, 53.10%, and 98.36% respectively under the treatment of H₂O₂. The PSⅡ non-photochemical quenching coefficient (NPQ), regulatory energy dissipation Y (NPQ), non-regulatory energy dissipation Y (NO), the proportion of absorbed light energy used for antenna heat dissipation (D), the proportion of non-photochemical dissipation of PS II reaction center (E_x), and the unbalanced deviation coefficient of excitation energy distribution between two optical systems (β/α-1) decreased by 34.13%, 35.15%, 30.26%, 35.52, 32.30%, and 53.43%, respectively. The mitigate effect was significant, but the mitigation effect tended to decline with the increase of exogenous concentration of H₂O₂. Comprehensive analysis showed that the mitigate effect of H₂O₂ on cadmium toxicity of Z. jujube was related to many physiological processes, such as improving photosynthesis of Z. jujube, maintaining the high activity of antioxidant system and improving photochemical efficiency of PS II. Among them, 0.08 mmol/L H₂O₂ was the best way to improve the repair efficiency of Z. jujube, which could be used as a strengthening measure of phytoremediation.

Abstract:Field experiments were conducted to study 11 common potato varieties in central south China. The contents of cadmium (Cd) and lead (Pb) in potato organs were determined to analyze the difference of Cd and Pb absorption and accumulation capacity in different varieties of potatoes. The achievement of this work could provide a practical reference for safe planting of potatoes in the areas soil polluted with heavy metals in central south China. The results showed that in the soil complexly polluted with Cd and Pb, the fresh weight of tuber, stem and leaf, and the contents of Cd and Pb in roots, stems and leaves, tubers of potato plants showed significant differences among 11 varieties. The contents of Cd in tuber ranged from 0.39 to 0.67 mg/kg, showing an exceeding the standard rate of 100%; the contents of Pb in tuber ranged from 0.16 to 0.43 mg/kg, exceeding the standard rate of 81.8%. The contents of Cd and Pb in different potato organs showed a distribution pattern as root > stem and leaf > tuber. The bioaccumulation factors of Cd and Pb in potato plants ranged from 2.35 to 5.56 and 0.11 to 0.22, respectively, indicating that bioaccumulation and translocation capacity of potato for Cd was greater than for Pb. Although the Total Target Hazard Quotient demonstrated that the TTHQ values of five kinds of potatoes such as Jinxiang were less than 1, the risk to human health was small, but combined with the Cd and Pb contents of tubers, it is recommended to be safer to use potatoes grown in contaminated areas as industrial raw materials.