Accumulation and leaching risk of phosphorus in vegetable soils under intensive cultivation.

In order to study accumulation and leaching risk of soil phosphorus,soil samples were collected from vegetable fields,different in intensive vegetable cultivation history(3-5,15-20 and 25-30 years) in the suburbs of Nanjing for assay of concentrations of total phosphorus(TP),available phosphorus(Olsen-P),dissolved reactive phosphorus(CaCl2-P) and bio-available phosphorus(NaOH-P),and P adsorption in 0-20 cm soil layer,and for assessment of soil phosphate leaching risk through determination of degree of phosphorus saturation(DPS) and maximum buffer capacity(MBC) of the soils.Results show that the longer the history of intensive vegetable cultivation,the higher the accumulation of phosphorus for all P fractions,except for NaOH-P,which was higher in soils of 3-5 a than in the other two groups.TP,Olsen-P,CaCl2-P and NaOH-P accumulated mainly in the 0-20 cm soil layer,and decreased in concentration with the depth in profile.DPS increased with the history.In the 0-5 cm soil layers of soils of 25-30 a,the concentration of DPS was even higher than 25%,the environmental sensitive index for soil P loss,while MBC was the lowest,suggesting that the leaching risk of soil phosphorus rises with the cultivation history,particularly in 0-5 cm soil layer.