@@1 Background Owing to vegetable's short growth-period, large amount of fertilizer used and frequent fertilization, concentrations of N (nitrogen) and P (phosphorus) in vegetable soils are higher than grain ones. In some areas, the amounts of chemical fertilizers so applied (N+P2O5+K2O, 3 000 kg.hm-2) are several times of that needed by vegetables. N and P have been obviously accumulated in the vegetable soils, resulting in excessive nitrate and poor quality of vegetables. Furthermore, a series of environmental problems are produced, i.e., the deterioration of physical and chemical properties of vegetable soils, the nitrate's pollution of vegetables, groundwater and the eutrophication of surface water. However, some traditional non-scientific water & fertilization managing measures, i.e., "Large amount of fertilizer and water is used frequently", "Fertilizer is applied flowing with irrigating water", etc., are adopted by most peasants on vegetable production. As a result, the quality of vegetable and water environment would be deteriorated more in the future, driving by the above factors.
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