氮肥施用过量,无论是无机N肥或有机肥都会在土壤中积累。特别是栽种浅根系和小根系的蔬菜地,土壤累积的NO₃^--N能淋洗到地下水使NO₃^-超标。在种植深根系和有较大根系的作物如稻、麦、玉米和棉花等大田粮食和经济作物的土壤,目前的施肥水平下尤其在作物生长期内一般不会有NO₃^-积累,也不可能污染地下水。
地表水体中85%以上是NH₄⁺-N,主要来源于人畜粪尿和有机肥,不是源于当季施入的无机N肥。保护水环境质量的重点应放在控制畜禽养殖业污染和城乡生活污水等非点源污染的治理上。温带地区大多数地表水体富营养化的限制因子是P。有机肥和无机P肥过量使用都会使土壤P不断累积。据在苏南太湖地区的调研证明,P素非点源污染中,农田进入水体的P(含水体下淤泥扩散的P)的相对贡献率不到10%,而畜、禽、人排泄物及生活污水、淡水养殖业等P的相对贡献率在90%左右。农田P进入水体的冬麦季比稻季多2~3倍。旱地中以蔬菜基地土壤P素累积最多(蔬菜基地多数在城市近郊)对水体污染威胁最大。为此,建议蔬菜基地最好从近郊迁移到较远的地区,该区种植结构可作相应调整。从经济效益、社会效益和生态效益综合考虑,保持足够面积的稻田,压缩冬麦面积,部分改种油菜或其它经济作物;部分种牧草养鹅,增加农民收入满足市场需求;部分种冬绿肥是可取的。

Overuse of N fertilizers either in mineral or in organic form will inevitably lead to N accumulation in soil where it is applied. In upland soil, nitrification of N is dominant, when it is grown with vegetable crops with a shallow and small root system in particular. The accumulated high content of nitrate N in the upper layer will certainly be leached down to the groundwater, bringing NO₃^- concentration above limit (50 mg/L). In fields grown with food and other economic crops such as wheat, corn or cotton with deeper and larger root systems, no extra NO₃^- will be left with the current fertilization rate during the growing season in particular, excluding the risk of polluting the groundwater.
About 80 % of the N in the surface water in the Taihu Lake region is in NH₄⁺-N form and most likely comes from human, livestock and poultry excreta, rather than seasonally applied mineral N fertilizer, as is identified by δ¹⁵ N method. So the key to protection of the water environment quality is to control non-point source pollution, like domestic sewage and livestock and/or poultry manure.
Phosphorus is the most contributive factor of water eutrophication in the temperature zone. Overuse of P fertilizers, in mineral or organic form, will build up soil P. According to the soil survey and field study, among all sources of rural and agricultural non-point source P pollution, domestic sewage, livestock and poultry manure (liquid or solid) and fish culture are the major ones, contributing about 90%, while P in runoff and drainage from the field entering the water system accounts for less than 10%. Soil P load to water is about 2~3 folds higher in the wheat season than in the rice season. Much higher accumulation of soil P in vegetable field than in food crops field. Therefore, it is suggested that vegetable fieldsshould be moved from the near suburban areas to further rural area, meanwhile the area for winter wheat could be reduced from this region. On other hand that the area for wetland rice should be kept as much as possible in summer, and in winter season, oil rapeseed crop, winter green manure crops or fallow with rice straw mulch are suggested considering food security, and environment friendly sustainable use of the soil resources.

国家重大基础研究规划项目(973)G19990118:土壤质量演变规律与持续利用研究的部分内容。