种植结构非粮化对农田氮磷流失负荷的影响

以浙江省慈溪市为案例区,通过建立非粮化指数(NGP)解析种植结构非粮化演变过程,并利用实地调查、文献调研和统计年鉴数据估算农田氮磷投入量和径流流失量,评估其对农田氮、磷径流流失负荷的影响,为深入认识种植结构非粮化的生态效应和合理管控农业面源污染提供科学基础。结果表明:1995—2019年,慈溪市的种植结构存在明显的非粮化趋势,粮食作物种植面积锐减49.3%,而蔬菜和水果种植面积分别增长113.8%和108.4%。根据NGP,慈溪的非粮化过程可以分为3个阶段:稳定上升期(1995—2007年),回调下降期(2007—2013年)和快速上升期(2013—2019年)。2001—2018年,慈溪市种植业氮、磷投入总量增幅分别为38.8%和249.5%。至2018年,慈溪市农田氮、磷流失负荷分别为2 823.3 t 和971.5 t。随着种植结构的非粮化,菜地已经取代稻田成为当地农田氮、磷流失的首要来源,占慈溪市种植结构年氮、磷流失总量的70.9%和89.2%,成为农业面源污染控制的重点对象。建议各地针对不同非粮化类型制定差异化的管控政策,并将农田氮、磷养分流失负荷加入土壤质量评价体系,为引导下一阶段的种植结构调整提供依据。

Effects of non-grain transition of agricultural planting structure on nitrogen and phosphorus loss from cultivated land

In the present study, Cixi City, Zhejiang Province, was selceted as the case area. The non-grain index (NGP) was eatablised to reveal the non-grain tansition process of agricultural planting structure in Cixi. Based on the field survey, literature research and statistical yearbook data, the amount of nitrogen and phosphorus input and runoff loss in cultivated land in Cixi was estimated, and the effect of non-grain transition of agricultural planting structure on nitrogen and phosphorus loss from cultivated land was evaluated, to provide scientific basis for in-depth understanding of the ecological effects of non-grain transition of agricultural planting structure and reasonable control of agricultural non-point source pollution. It was shown that there was a shift from grain crops to cash crops in agricultural planting structure in Cixi from 1995 to 2019. Judged by the established NGP, this shift processs could be divided into three periods: a stable rise period (1995-2007), a fallback (2007-2013) period, and a rapid rise period (2013-2019). During 1995-2019, the planting area of grain crops fell sharply by 49.3%, while the planting area of vegetables and fruits increased by 113.8% and 108.4% respectively. From 2001 to 2018, the growth rates of total nitrogen and phosphorus input of planting structure in Cixi reached 38.8% and 249.5%, respectively. By 2018, the nitrogen and phosphorus runoff losses of planting structure in Cixi were 2 823.3 t and 971.5 t, respectively. With the non-grain transition of agricultural planting structure, the vegetable field has replaced paddy field as the primary source of nitrogen and phosphorus loss from planting structure, which accounted for 70.9% and 89.2%, respectively, of the total annual nitrogen and phosphorus loss from the planting structure in Cixi, and has become a key target for agricultural non-point source pollution control. It was suggested that different regions should formulate differentiated management and control policies for different types of non-grain production, and the loss of nitrogen and phosphorus should be added to the soil quality evaluation system to provide basis for guiding the next stage of planting structure adjustment.