To better understand the adsorption and transport of Cd2+ in soils, column experiments were conducted with various soils and inflow solutions with different pH values. Breakthrough curves (BTCs) of the column tests we...To better understand the adsorption and transport of Cd2+ in soils, column experiments were conducted with various soils and inflow solutions with different pH values. Breakthrough curves (BTCs) of the column tests were fitted using both the equilibrium and non-equilibrium models installed in the program of CXTFIT. Results showed that the equilibrium model fitted most of BTCs reasonably well. Values of the retardation factor (R) and the distribution coefficient (kd) for Cd2+ adsorption and transport increased with increasing pH values of the inflow solution and of the soil. However, the clay content was not a key factor to affect R and kd for Cd2+ adsorption and transport. The average dispersivity values and the variance values of dispersivity increased with increasing clay content of the soils.展开更多
Irrigation practices greatly affect sustainable agriculture development. In this study, we investigated the effects of irrigation efficiency on water flow and chemical transport in soils, which had significant impact ...Irrigation practices greatly affect sustainable agriculture development. In this study, we investigated the effects of irrigation efficiency on water flow and chemical transport in soils, which had significant impact on the environment. Field dye staining experiments were conducted at different soils with various irrigation amount. Image analysis was conducted to study the heterogeneous flow patterns and their relationships with the irrigation efficiency. Irrigation efficiency and its environmental effects were evaluated using various indictors, including application efficiency, deep percolation ratio, storage efficiency, and uniformity. Under the same irrigation condition, soil chemical distributions were more heterogeneous than soil water distributions. The distributions were mainly affected by soil texture, initial soil water content, and irrigation amount. Storage efficiency, irrigation uniformity, and deep percolation ratio increased with irrigation amount. Since the chemical distribution uniformity was lower than the water uniformity, the amount of chemical leaching increased sharply with decrease of irrigation uniformity, which resulted in high environmental risks of groundwater pollution.展开更多
The soil water retention curve is an important hydraulic function for the study of flow transport processes in unsaturated soils. The objective of this study was to develop a soil water retention function using a gene...The soil water retention curve is an important hydraulic function for the study of flow transport processes in unsaturated soils. The objective of this study was to develop a soil water retention function using a generalized fractal approach. The model exhibits asymmetry between the solid phase and pore phase, which is in marked contrast to the symmetry between phases present in a conventional fractal model. The retention function includes 4 parameters： the saturated water content θs, the air entry value ha, the fractal dimension Df, and an empirical parameter β, characterizing the complicated soil pore structures. Sixty one data sets, covering a wide range of soil structure and textural properties, were used to evaluate the applicability of the proposed soil water retention function. The retention function is shown to be a general model, which incorporates several existing retention models. The values of β/θs and （θs-θr ）/β were used as indexes to quantify the relationships between the proposed retention function and the existing retention models. The proposed function fits all the data very well, whereas other tested models only match about 16%-48% of the soil retention data.展开更多
基金Supported by the National Natural Science Foundation of China (Grant No. 50839002)the National Hi-Tech Research and Development Program of China ("863" Project) (Grant No. 2006AA100209-04)
文摘To better understand the adsorption and transport of Cd2+ in soils, column experiments were conducted with various soils and inflow solutions with different pH values. Breakthrough curves (BTCs) of the column tests were fitted using both the equilibrium and non-equilibrium models installed in the program of CXTFIT. Results showed that the equilibrium model fitted most of BTCs reasonably well. Values of the retardation factor (R) and the distribution coefficient (kd) for Cd2+ adsorption and transport increased with increasing pH values of the inflow solution and of the soil. However, the clay content was not a key factor to affect R and kd for Cd2+ adsorption and transport. The average dispersivity values and the variance values of dispersivity increased with increasing clay content of the soils.
基金Supported by the NSFC (Grant Nos. 50779098, 50579079)the National Basic Research Program of China ("973" Project) (Grant No. 2006CB403404)
文摘Irrigation practices greatly affect sustainable agriculture development. In this study, we investigated the effects of irrigation efficiency on water flow and chemical transport in soils, which had significant impact on the environment. Field dye staining experiments were conducted at different soils with various irrigation amount. Image analysis was conducted to study the heterogeneous flow patterns and their relationships with the irrigation efficiency. Irrigation efficiency and its environmental effects were evaluated using various indictors, including application efficiency, deep percolation ratio, storage efficiency, and uniformity. Under the same irrigation condition, soil chemical distributions were more heterogeneous than soil water distributions. The distributions were mainly affected by soil texture, initial soil water content, and irrigation amount. Storage efficiency, irrigation uniformity, and deep percolation ratio increased with irrigation amount. Since the chemical distribution uniformity was lower than the water uniformity, the amount of chemical leaching increased sharply with decrease of irrigation uniformity, which resulted in high environmental risks of groundwater pollution.
基金Supported by the National Basic Research Program of China (973 Program) (2010CB951102)the National Natural Science Foundation of China (51039007, 50979076)the Open Research Fund of Key Laboratory for Water Requirement and Regulation, Ministry of Agriculture (CWRR200901)
文摘The soil water retention curve is an important hydraulic function for the study of flow transport processes in unsaturated soils. The objective of this study was to develop a soil water retention function using a generalized fractal approach. The model exhibits asymmetry between the solid phase and pore phase, which is in marked contrast to the symmetry between phases present in a conventional fractal model. The retention function includes 4 parameters： the saturated water content θs, the air entry value ha, the fractal dimension Df, and an empirical parameter β, characterizing the complicated soil pore structures. Sixty one data sets, covering a wide range of soil structure and textural properties, were used to evaluate the applicability of the proposed soil water retention function. The retention function is shown to be a general model, which incorporates several existing retention models. The values of β/θs and （θs-θr ）/β were used as indexes to quantify the relationships between the proposed retention function and the existing retention models. The proposed function fits all the data very well, whereas other tested models only match about 16%-48% of the soil retention data.
