Phosphorus leaching losses in different planting farmlands in the riverine plain area of Taihu Lake

The method of soil solution collection by soil solution extractor was employed to explore the relationship between Olsen-P accumulated in soil and P concentration in leakage in different types of planting farmlands in Taihu Lake Basin. The results indicate that there are higher application rates of N and P fertilizers on vegetable fields and orchards in the experiment areas. The yearly average pure P application rates are about 946.8 kg/ha in vegetable fields, and 832.6 kg/ha in orchards, which are 10-12 times of that in paddy plots (83.6 kg/ha). The applied fertilizer P is mostly retained in the surface soil，Olsen-P is accumulated in 0–5 cm soil layer, and Olsen-P contents are 161.75 mg/kg, 143.88 mg/kg and 23.77 mg/kg in vegetable fields, orchards and paddy plots, respectively. Olsen-P in vegetable fields and orchards is about 6–8 times higher than that in paddy plots. Olsen-P contents are reduced sharply with the increase of soil depth in farmlands. Dissolvable phosphorus content is much higher than particulate phosphorus content in the lower leakage. There is a significant exponential relationship between Olsen-P accumulated in soil and dissolvable reactive phosphorus concentration in lower leakage, indicating that the risk of P leaching losses increases significantly when Olsen-P exceeded some level in soil.