Phosphorus saturation degree of soils on vegetable farms and its effects on soil phosphorus release potential and water quality

Phosphorus losses from agricultural soils to water can pose a threat to water quality.The concern over P with respect to water quality is its stimulation on algae and other aquatic plant growth.Phosphorus inputs to agricultural soils that are regularly fertilized with mineral P can exceed crop requirement.This over-supplied P often results in excessive P accumulation in the soil,and such soils represent a potential diffuse source of pollution as P for the eutrophication of surface waters.Little information is available on the release intensity of P to water from vegetable soils and its relation to the P saturation degree in the soils.In this study,33 surface soil samples and 17 soil profiles with a wide range of total P,and runoff and groundwater samples were collected from various vegetable fields in Zhejiang province.Results showed that long-term over application of P could elevate P saturation degree,increased P release potential from the soils.Phosphorus release intensity measured by means of dialysis was positively correlated with soil P accumulation,and increased significantly with P saturation degree of the soils.Increased soil P saturation degree could increase P concentrations in surface waters and groundwater.The P concentration in surface runoff increased slowly with increasing P saturation degree when P saturation degree was below 25%,but it increased rapidly when P saturation degree was over 25%.The P concentration in surface waters was mainly correlated with P saturation degree of the surface soils,whereas the P concentration in groundwater was controlled by P saturation degree of subsurface soils.These results indicated that soil P saturation degree could efficiently characterize soil P release potential and its impaction on the environments.