Study On Nitrogen And Phosphorus Movement And Control In Vegetable Fields In Taihu Lake Region

Nitrogen (N) and phosphorus (P) losses with agricultural non-point is one of major factors in resulting in eutrophication of surface waters. Distinguish of risk area of loss of soil N and P from vegetable fields to water body, pathways, fluxes and chemical forms of N and P in runoff from vegetable fields is critical to control eutrophication of water body. In the present study, about 50 hm² vegetable field located at Dapu town, Yixing city was selected to investigate spatial variability of soil N and P, to determine phosphorus leaching"Threshold", and to evaluate risk of leaching loss of N and P from vegetable fields, to estimate soil N and P runoff export from vegetable fields, and to assess control efficiency of grass buffer zone on runoff export from vegetable fields into water body. Major results were summarized as bellow.In the present investigation, total 156 top layer soil samples (0～20 cm) were taken in a regular grid of 50 m by 50 m at 50 hm² area of vegetable field. Characteristics of spatial variability and distribution pattern of soil N, P were determined using GIS and geo-statistics, Spatial variation-structure of total nitrogen, total P and available P were obvious, Semivariograms for soil available P were well fitted by linear to sill model after logarithm change , Total N and total P well fitted by exponential model.Spatial correlation in total P and available P were moderate ,respectively . High– P fields appeared at shores of Zhudu, and Linzhuan harbors and these fields could be a risk area for loss of soil N, and P from vegetable land to water body, which must take measures to control loss of N and P from vegetable fields to water body.The 0.01mol.L^-1 CaCl₂ extractable P was very little from soils below 60 mg.kg^-1 M1-P (termed the change point), however CaCl₂ extractable P above the Change-Point was linearly related to the soil Bray-P. We therefore suggest that the change point of around 60 mg.kg^-1 M1-P is a critical concentration at which leaching of P starts for the study vegetable soil. The soil columns study further revealed that it is reasonable about this change point. The critical value was to use to estimate the risk of P leaching from vegetable field to water. About 28%...