太行山前平原农田生态系统氮素循环与平衡研究

Nitrogen cycling and balance in agricultural ecosystem in piedmont plain of Taihang Mountains

在中国科学院栾城生态农业试验站1公顷小麦—玉米轮作农田,运用乙炔抑制—原状土柱培育法、微气象学法和陶土头多孔杯—水量平衡法分别定量测定了氮素硝化—反硝化损失、氨挥发、NO3--N淋溶损失等氮素循环转化途径。研究结果表明,每年因氨挥发而造成的肥料氮损失量为N 60 kg/hm2,占施入肥料氮的15%;NO3--N淋溶损失量为N 68~4 kg/hm2,占肥料施用量的1.4%2~0.3%;每年因硝化—反硝化过程造成的肥料损失量为N 2.021~0.49 kg/hm2,占肥料施入量的0.51%1~.37%。氨挥发、NO3--N淋溶和硝化—反硝化损失主要发生在施肥灌溉/降雨之后,玉米季肥料损失明显高于小麦生长季节。氨挥发和NO3--N淋溶损失是本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。在当地农民所采用的常规农业管理措施下,小麦—玉米轮作农田氮素平衡处于盈余状态,小麦季盈余N+115.5^+124.5 kg/hm2,明显高于玉米季;由于玉米季氮素损失严重,氮素盈余较少,甚至出现亏缺,玉米季氮素平衡状况为-54.6^+14.3 kg/hm2。

The piedmont plain of MT Taihang, an important agricultural area in North China, usually growing wheat in winter and maize in summer, is characterized by intensive cereal production. For the purpose of maximizing crop yield, irrigation and N fertilizer are commonly oversupplied. As the result large N is lost via volatilization, denitrification and leaching and come into being a great harm to the environment. The main nitrogen cycling pathways, such as nitrificationdenitrification, ammonia （NH3） volatilization, nitrate （NO3^-N） leaching and N uptake by crops, were monitored in a wheat-maize rotation field with acreage being one hectare. The dominant N loss way was evaluated. The characters of N inputs and outputs on farmland of Piedmont Plain of MT Taihang were quantificationally illuminated and the N balance was analyzed so as to provide some important information for establishing optimized N management to diminish N losses and increase N use efficiency. The results indicated that NH3 volatilization and NO3^- -N leaching losses were the dominant pathways of N loss resulting in low N use efficiency. The annual NH3 volatilization rate was N 60 kg/ha and NO3^- - N leaching loss rate was N 6--84 kg/ha, accounting for 15% and 1.4%--20.3% of the applied N fertilizer, respectively. The nitrification-denitrification loss was not a very important pathway of N loss, but its effect on environment cannot be ignored. The annual nitrification-dinetrification loss was N 2.02--10.49 kg/ha, accounting for 0.51%--1.37% of applied N. NH3 volatilization, nitrification- denitrification and NO3^- -N leaching mainly took place after N applied and irrigation or heavy rainfall events occurred and the N loss in the time of maize growing was much larger than that of winter wheat growing. The N was oversupplied in wheat-maize rotation field under traditional agricultural management in the study area. The range of N surplus under wheat was N ＋ 115.5- ＋ 124.5 kg/ha, higher than those under maize. The N balance under maize was lightly surplus or wane resulted from heavy N loss. The measurements should be taken, such as improving N applied methods to decrease NH3 volatilization, reducing irrigation amount especially avoiding heavy irrigation to diminish NO3^- -N leaching, to improve crop yields and N use efficiency.