蔬菜的硝态氮累积及菜地土壤的硝态氮残留

在不同季节对11类、48种蔬菜的测定表明,硝态氮含量高于325mg·kg^-1,达到4级污染水平的有20种,占调查总数的41.7%,包括全部叶菜类、部分瓜类、根菜类和葱蒜类蔬菜.其中硝态氮含量高于700mg·kg^-1,超过4级污染水平的有5种,均为叶菜类蔬菜.叶菜硝态氮累积虽为严重,但其中部分蔬菜叶片的硝态氮含量却低于3级污染水平对不同类型菜地和农田土壤的测定发现,菜地0～200cma各土层的硝态氮残留量均高于农田土壤,常年露天菜地200cm土层的硝态氮残留总量为1358.8kg·hm^-2年大棚菜田为1411.8kg·hm^-2,5年大棚则达1520.9kg·hm^-2,而一般农田仅为245.4kg·hm^-2.菜地土壤的硝态氮残留严重威胁菜区地下水环境.

Nitrate Accumulation in Vegetables and Its Residual in Vegetable Fields

Determinations of 11 kinds, 48 varieties of vegetables were carried out at different seasons. The results showed that nitrate-N concentrations in 20 vegetables reached Pollution Level 4 (NO₃^--N>325 mg·kg^-1), which accounted for 41.7% of the total number of the sampled vegetables and included all of the leafy, and most of the melon, root, onion and garlic vegetables. Among them, 5.leafy vegetables even exceeded Level 4 (NO₃^--N>700 mg·kg^-1). Although leafy vegetables were usually apt to heavily accumulate nitrate, most of them were with nitrate-N concentrations lower than Level 3 (NO₃^--N<325 mg·kg^-1) in leave blades. Further investigation showed that vegetable soils accumulated more nitrates in each layer from 0 cm to 200 cm than did cereal crop soil. The total amount of residual nitrate-N was 1358.8kg·hm^-2 in the 200 cm soil profile of usual vegetable fields, and 1411.8kg·hm^-2 and 1520.9kg·hm^-2 in the 2-yaers and the 5-years long plastic greenhouse fields respectively, however that in the cereal crop fields was only 245.4 kg·hm^-2. Nitrate residual in vegetable soils formed serious threats to underground water in vegetable growing areas.