基于硝态氮淋失源头控制的华北春玉米施氮阈值研究

In China’s farmland, excessive nitrogen application is relatively common and it also has a serious problem that nitrate in groundwater is exceeding the corresponding standard because of nitrate leaching during rainy season, which has threatened the safety of drinking water. Identifying the optimal nitrogen application is one of the most important methods to resolve such issue from the source. However, the critical nitrogen application (i.e. nitrogen application threshold) of crops, which causes exceeded nitrate in groundwater, is still unclear. The project will take spring maize as the research object based on nitrate-nitrogen leaching control and groundwater quality protection. On the basis of large-scale lysimeters, simulated rainfall and DNDC simulation will be also used to elucidate the characteristics and dominating factor of nitrogen leaching. The response relationship between nitrogen application rate and nitrogen leaching as well as nitrate nitrogen content of groundwater will be quantitated. The maximum nitrate leaching loss allowed in the farmland will be determined and then nitrogen threshold will be identified based on nitrogen leaching prevention. According to the key factor and critical period of leaching, the optimal fertilization strategy will be formulated to deal with risk of yield and leaching. The results of the project will provide a theoretical basis for developing the reduced fertilization decision-making and the successful prevention of nitrogen pollution caused by nitrogen leaching.

我国农田过量施氮现象较为普遍，雨季氮素淋失严重，由此引起的地下水硝酸盐超标已威胁到人们的饮用水安全，确定合理施氮量是从源头解决这一问题的重要方法之一。然而，目前对造成地下水硝酸盐超标的农田作物临界施氮量（施氮阈值）仍不清楚。本项目拟以华北典型农田为研究对象，以硝态氮淋失控制和地下水质保护为目标，在大型渗漏池原位监测的基础上，与人工模拟降雨和DNDC模拟方法相结合，研究农田氮素淋失的主要发生特征和主控因子，量化氮肥施用量与氮素淋失以及地下水硝态氮含量之间的响应关系，明确农田允许的最大硝态氮淋失量，提出基于氮淋失防控的施氮阈值控制总量；识别年度淋失关键时期和单次淋失关键因子，提出应对产量风险和淋失风险的合理氮肥施用策略。该研究将为国家制定减量施肥决策、缓解华北农田氮淋失造成的地下水硝酸盐污染提供理论依据。

我国农田过量施氮现象较为普遍，雨季氮素淋失严重，由此引起的地下水硝酸盐超标已威胁到人们的饮用水安全，确定合理施氮量是从源头解决这一问题的重要方法之一。然而，目前对造成地下水硝酸盐超标的农田作物临界施氮量（施氮阈值）仍不清楚。本项目以华北典型农田为研究对象，以硝态氮淋失控制和地下水质保护为目标，在大型渗漏池原位监测的基础上，与人工模拟降雨和DNDC模拟方法相结合，研究了农田氮素淋失的主要发生特征和主控因子，量化了氮肥施用量与氮素淋失以及地下水硝态氮含量之间的响应关系，明确了农田允许的最大硝态氮淋失量，提出了基于氮淋失防控的施氮阈值控制总量；识别了年度淋失关键时期和单次淋失关键因子，提出了应对产量风险和淋失风险的合理氮肥施用策略。各年度的总氮和硝态氮淋失量均随施氮量的增加而增加，高量施氮处理的氮素淋失量明显高于低量施氮和不施氮处理，硝态氮是淋失水中主要的氮素形态。有淋失事件的年份内平均年度淋失水量为78.3 mm，若使这些淋溶水均满足地下水III类水标准（硝态氮浓度<20 mg/L），则农田可允许的最大硝态氮淋失量为15.7 kg/hm2；根据施氮量与产量和氮素淋溶量的双效应曲线，华北平原典型春玉米适宜施氮量为150 kg/hm2，环境施氮阈值为240 kg/hm2。为了减少氮素淋失风险，在满足作物养分需求和产量产出的情况下，春玉米农田生产实践过程中，应当将传统的两次施肥改为三次施肥，基肥施用三分之一，翻入土壤或条施、穴施，在6月中旬施用三分之一，避开7月追肥，剩余三分之一在8月上旬施用，此时氮素淋失风险较低。该研究结论将为国家制定减量施肥决策、缓解华北农田氮淋失造成的地下水硝酸盐污染提供理论依据。