N and P accumulation status and their leaching potential in vegetable fields in Fujian Province

Soil tests and leakage water simulation experiment using earth pillar were used to study NO-3-N and Olsen-P content and their leaching in 460 vegetable field samples, which were collected from the topsoil of typical vegetable fields in Fujian province. Soil test results show that the NO-3-N and Olsen-P contents in the top soils were averaged 47.455.5 mg/kg and 61.743.2 mg/kg respectively. Thereinto, the NO-3-N and Olsen-P content in the fields growing melon and fruit vegetables was apparently higher than those in the fields growing leaf and tuber vegetables. Calculated with the double-velocity turning point model, the critical index of double-velocity turning point X0 of N and P leaching is 76.3 mg/kg for NO-3-N and 42.8 mg/kg for Olsen-P, which is equivalent or a bit higher than the agricultural indices for the satisfactory vegetable nutrition. When the NO-3-N or Olsen-P contents in soil were lower than their X0, the NO-3-N or total-P concentration in leaching water increases slowly in a linear way, when the NO-3-N or Olsen-P contents in soil exceeds its X0, the NO-3-N or total-P would increases rapidly in non-linear way. There are 17.9% and 81.3% of soil samples with their NO-3-N and Olsen-P content exceeded their X0 respectively, indicating the high N and P leaching potential. In the melon and fruit vegetable fields, in about 32.3% and 96.3% of soil samples the NO-3-N and Olsen-P contents exceeded their X0 respectively, indicating their N and P leaching potential were apparently higher than the leaf vegetable and tubers vegetable fields. More attention should be taken on the melon and fruit vegetable fields to control N and P pollution.