Due to the growing concern about the agricultural phosphorus (P) losses pollution, an in-depth understanding of P in paddy soils of China would be helpful in providing a national perspective of the environmental impac...Due to the growing concern about the agricultural phosphorus (P) losses pollution, an in-depth understanding of P in paddy soils of China would be helpful in providing a national perspective of the environmental impact of P cycling and fertility on China's farms. In this study, we evaluated the P storage and the P density of paddy soils in China, characterized the spatial variations of P among the subgroups of paddy soils and soil regions in China, and evaluated the P data using GIS-based analysis, which included a newly compiled 1:1 000 000 digital soil map of China, and using 1 490 soil profiles. The available and total P densities of paddy soils were 6.7 and 698.5 g m -3 , respectively. Overall in China, the total P storage within 1 m of paddy soils was estimated to be 330.2 Tg. The P density of paddy soils varied substantially with subgroups due to the different soil water regimes such as groundwater table and soil drainage. The P availability in paddy soils, especially in surface layer, was higher in high temperature and precipitation areas. Further research is needed to examine more anthropogenic impact factors, such as increasing use of chemical fertilizer.展开更多
Accurately calculating detachment capacity is the most fundamental issue when establishing a soil erosion process model.Colluvial deposits of Benggang are typical soil-gravel mixtures,whereas the understanding of the ...Accurately calculating detachment capacity is the most fundamental issue when establishing a soil erosion process model.Colluvial deposits of Benggang are typical soil-gravel mixtures,whereas the understanding of the soil detachment of colluvial deposits is limited.This work investigated the effects of the gravel contents on the soil detachment capacity of colluvial deposits and its hydrodynamic mechanism.The colluvial sample was collected in Anxi County,Fujian Province,Southeast China,and a small-sample scouring test was used.The slope steepness ranged from 18%to 84%,unit discharge ranged from 0.56×10^(-3)to 2.22×10^(-3)m^(2)s^(-1),and gravel content ranged from 0%to 70%.The results indicated that the gravel content is the primary factor that influences the detachment capacity,followed by the discharge and then the slope.The detachment capacity trend with the gravel content varied over different slopes and discharges.Stream power represents the best hydrodynamic parameter for modelling the detachment capacity of colluvial deposits and can be used to establish a fitting equation for the colluvium together with the mean weight diameter(MWD)(Nash-Sutcliffe efficiency(NSE)=0.96).As the gravel content increased,the soil erodibility parameters increased several folds,in some cases more than 10 folds,mainly because the soil shear strength decreased gradually.Meanwhile,as the gravel content increased,the gravel specific surface area increased,the obstruction of gravel to runoff increased,and the energy needed for runoff to overcome gravel obstruction increased,leading to 2-3 folds higher critical shear stress of runoff for soilgravel mixtures compared with pure soil.In summary,gravel can influence the detachment capacity by changing the soil properties,and the gravel content also affects the relationship between soil detachment capacity and the hydrodynamic parameters.These findings deepen the understanding of the influence of gravel on soil erosion and provide a basis for establishing a soil erosion process model in colluvial deposits.展开更多
基金Project supported by the National Key Basic Research Program (973 Program) of China (No. 2007CB407206)the National Natural Science Foundation of China (No. 40621001)the Frontier Project of the Chinese Academy of Sciences (No. ISSASIP0715)
文摘Due to the growing concern about the agricultural phosphorus (P) losses pollution, an in-depth understanding of P in paddy soils of China would be helpful in providing a national perspective of the environmental impact of P cycling and fertility on China's farms. In this study, we evaluated the P storage and the P density of paddy soils in China, characterized the spatial variations of P among the subgroups of paddy soils and soil regions in China, and evaluated the P data using GIS-based analysis, which included a newly compiled 1:1 000 000 digital soil map of China, and using 1 490 soil profiles. The available and total P densities of paddy soils were 6.7 and 698.5 g m -3 , respectively. Overall in China, the total P storage within 1 m of paddy soils was estimated to be 330.2 Tg. The P density of paddy soils varied substantially with subgroups due to the different soil water regimes such as groundwater table and soil drainage. The P availability in paddy soils, especially in surface layer, was higher in high temperature and precipitation areas. Further research is needed to examine more anthropogenic impact factors, such as increasing use of chemical fertilizer.
基金funded primarily by grants from the Natural Science Foundation of Fujian Province of China(2021J01120)the National Natural Science Foundation of China(41977071)。
文摘Accurately calculating detachment capacity is the most fundamental issue when establishing a soil erosion process model.Colluvial deposits of Benggang are typical soil-gravel mixtures,whereas the understanding of the soil detachment of colluvial deposits is limited.This work investigated the effects of the gravel contents on the soil detachment capacity of colluvial deposits and its hydrodynamic mechanism.The colluvial sample was collected in Anxi County,Fujian Province,Southeast China,and a small-sample scouring test was used.The slope steepness ranged from 18%to 84%,unit discharge ranged from 0.56×10^(-3)to 2.22×10^(-3)m^(2)s^(-1),and gravel content ranged from 0%to 70%.The results indicated that the gravel content is the primary factor that influences the detachment capacity,followed by the discharge and then the slope.The detachment capacity trend with the gravel content varied over different slopes and discharges.Stream power represents the best hydrodynamic parameter for modelling the detachment capacity of colluvial deposits and can be used to establish a fitting equation for the colluvium together with the mean weight diameter(MWD)(Nash-Sutcliffe efficiency(NSE)=0.96).As the gravel content increased,the soil erodibility parameters increased several folds,in some cases more than 10 folds,mainly because the soil shear strength decreased gradually.Meanwhile,as the gravel content increased,the gravel specific surface area increased,the obstruction of gravel to runoff increased,and the energy needed for runoff to overcome gravel obstruction increased,leading to 2-3 folds higher critical shear stress of runoff for soilgravel mixtures compared with pure soil.In summary,gravel can influence the detachment capacity by changing the soil properties,and the gravel content also affects the relationship between soil detachment capacity and the hydrodynamic parameters.These findings deepen the understanding of the influence of gravel on soil erosion and provide a basis for establishing a soil erosion process model in colluvial deposits.
