华北山前平原农田生态系统氮通量与调控

针对华北太行山前平原冬小麦-夏玉米轮作农田, 研究农田常规施肥400 kg(N)·hm^-2·a^-1]条件下作物氮素吸收与损失通量过程, 并根据各氮素输出通量特征开展管理调控。研究结果表明, 全年小麦-玉米轮作农田系统氮输入总量为561~580 kg(N)·hm^-2, 输出量468~494 kg(N)·hm^-2, 两季作物总盈余86~93 kg(N)·hm^-2, 其中有机氮为24~36 kg·hm^-2。氨挥发和NO₃^--N 淋溶损失是该区域农田氮素损失的主要途径, 是氮肥利用率低的重要原因。平均每年因氨挥发而造成的肥料氮损失量为60 kg(N)·hm^-2, NO₃^--N 淋溶损失量为47~84kg(N)·hm^-2, 两者占施肥总量的30%。每年因硝化-反硝化过程造成的肥料损失很小, 仅为5.0~8.7 kg(N)·hm^-2。通过施肥后适时灌水、合理调控灌水时间与用量, 以及利用秸秆还田与肥料混合施用等管理措施可改善氮素的迁移和转化规律, 有效减少氨挥发和NO₃^--N 淋溶损失, 并结合缓/控释肥与精准施肥技术, 充分利用土壤本身矿质氮素, 可有效提高养分利用效率和作物产量, 改善农田生态环境与促进农业持续和谐发展。

Nitrogen flux and its manipulation in the cropland ecosystem of the North China Plain

The North China Plain (NCP) is one of the areas of intensive cereal production in China, producing large winter wheat and summer maize. A critical challenge facing the agro-production sector of the NCP, however, includes over-application of chemical fertilizers, excessive soil nutrient accumulation and declining nutrient use efficiency. This study investigated relationship between nitrogen (N) flux and crop nutrient uptake/loss processes under conventional fertilization at 400 kg(N)·hm^-2·a^-1 in the winter wheat/summer maize crop rotation system in the piedmont region of NCP. The management practices of the fields were adjusted on the basis of the characteristics of N output fluxes. The results showed that in the region, a total N input of 561~580 kg·hm^-2 and output of 468~494 kg·hm^-2 resulted in a N surplus of 86~93 kg·hm^-2 per year. Organic N load in the study area was 24~36 kg·hm^-2. N loss via ammonia volatilization and NO₃^--N leaching was 60 kg·hm^-2 and 47~84 kg·hm^-2 per year, respectively, collectively accounting for 30% of applied N fertilizer in the region. N loss via nitrification-denitrification was only 5.0~8.7 kg·hm^-2 per year, accounting for 1%~2% of applied N fertilizer. Ammonia volatilization and NO₃^--N leaching were the main modes of N loss, and therefore the main drivers of lower N fertilizer utilization rate in the study area. Appropriate management practices such as adjustments of the rates and time of N fertilization and irrigation were important for decreasing ammonia volatilization, NO₃^--N accumulation in deep soil profile and therefore the mitigation of NO₃^--N loss in the region. Amendments with wheat/corn straw changed the rates of N transformation and migration in the soil, which also resulted in low NH₃ loss and NO₃^--N leaching. Analysis of precision fertilization via NO₃^--N or hyper-spectra information feature also showed that the main indices of N loss were the amount of soil available nutrient and crop nutrient content. This laid the basis for efficient fertilizer application in the study area. Control-release fertilizer and precision fertilization techniques improved crop nutrient uptake, which in turn increased N use efficiency. An integrated fertilizer utilization technique for sustainable environmental and agricultural development in the piedmont region of NCP was possible.