浙北平原不同种植年限蔬菜地土壤氮磷的积累及环境风险评价

长期过量施肥可导致蔬菜地土壤养分大量累积、养分利用效率下降和环境污染风险增加。以浙北平原不同种植年限蔬菜地土壤为研究对象,采用化学测试方法研究了菜地土壤氮和磷的积累及其淋失潜力的变化。结果表明,随着种植年限的增加,蔬菜地土壤全磷、有效磷（Olsen P）和NO3-N呈明显的积累;蔬菜种植年限为〈2、2～5、6～10、11～20、20～30和＆gt;30a的表土全P平均分别为0.66、0.75、1.07、1.49、2.40和2.12g·kg-1,有效P平均分别为13.2、37.8、42.2、70.2、137.9和101.7mg·kg-1,NO3-N平均分别为9.15、13.58、50.18、46.48、73.28和74.20mg·kg-1,同时土壤N和P垂直下移渐趋明显。土壤水溶性磷含量随土壤有效磷（OlsenP）积累的变化存在一个明显的突变点,相对应的土壤OlsenP临界值约为60mg·kg-1。随着种植年限增长,蔬菜地地表径流中氮和磷浓度呈明显增加,利用年限为20～30a的蔬菜地径流中可溶性P和NO3-N浓度分别约为利用年限〈2a蔬菜地的13.12和9.48倍。研究认为,长期超量施肥已导致这一地区蔬菜地土壤养分的过度积累，在蔬菜生产中应重视和提倡平衡施肥，控制土壤氮磷的积累。

Accumulation and Environmental Risk of Nitrogen and Phosphorus in Vegetable Soils with Different Plantation History in Northern Zhejiang

The losses of phosphorus（P） and nitrogen（N） from agriculture to waters have increased over the past few decades as a result of increased intensive farming and the development of a more industry-based type of agriculture. Long-term application of P and N with chemical fertilizers and animal manure in amounts exceeding removal with crops leads to buildup of P and N in soil, reduce of nutrient use efficiency, and to increasing risk of P and N losses to surface water and eutrophication. In this paper, 51 profiles of vegetable soils with different plantation history were sampled from the northern Zhejiang, and accumulation of nitrogen and phosphorus in the soils were characterized by means of chemical methods. Environmental risks of N and P losses in the vegetable soils were evaluated. The results showed that, as increase of plan- tation time, accumulation of total P, available P, and NO3-N in surface soils increased significantly, and downward movement of N and P in the soils was also enhanced. Mean total P concentrations in vegetable soils with plantation times of 〈2, 2-5, 6-10, 11-20, 20-30, and〉30 a were 0.66, 0.75, 1.07, 1.49, 2.40 and 2.12 g.kg-1, respectively. Mean Olsen P concentrations in the soils with plantation times of 〈2, 2-5, 6- 10, 11-20, 20-30, and 〉30 a were 13.2, 37.8, 42.2, 70.2, 137.9, and 101.7 mg kg-l, and those of NO3-N were 9.15, 13.58, 50.18, 46.48, 73.28, and 74.20 mg. kg-1, respectively. There was a change point of soil Olsen P（60 mg.kg-1）, above which the potential of soil P release increased sharply with soil Olsen P, and dissolved P was linearly related to soil Olsen P concentrations. Concentrations of dissolved P and N in- creased rapidly with increasing plantation time. Concentrations of dissolved P and NO3-N in runoff from the vegetable soil with plantation times of 20N30 a were about 13.12 and 9.48 times of those from vegetable soil with plantation times of 〈2 a. This situation was so serious that the quality of soil and groundwater in the area was deteriorating. Growers were facing potentially disruptive regulations aimed at improving the quality of both surface and ground water. Significant improvement in nutrient management would be required to meet this regulatory chal- lenge. Environmental protection and high crop yields could be achieved by avoiding the application of more nutrients than were actually re- moved from the fields. Thus, an integrated approach to nutrient management was needed, with best management practices （BMPs） targeted to critical areas of a watershed that contributed most of the P and N exported. Differing levels of nutrient management might be appropriate for different vegetable lands in the area. The overall goal of efforts to reduce N and P losses from the vegetable lands should be to balance off- farm N and P inputs in fertilizers with outputs in harvested products, while managing soils in ways that maintain productivity. It was likely that significant changes in the vegetable production systems might be necessary to achieve the ultimate goal of achieving nutrient balance.