华北太行山前平原农田土壤水分动态与氮素的淋溶损失

NITRATE LEACHING IN WHEAT-MAIZE ROTATION FIELD IN THE NORTH CHINA PLAIN

通过采集土壤溶液并分析其硝态氮（NO3^--N）含量，结合水量平衡方法，研究了华北太行山前平原小麦-玉米轮作农田在当前农民普遍采用的农业管理措施下土壤NO3^--N迁移、累积特征，计算了深层土壤水分渗漏与NO3^--N淋溶损失量。结果表明，土壤水分渗漏、NO3^--N的分布及其淋溶损失存在着明显的时空变异性，土壤水分的深层渗漏和NO3^--N的淋溶损失发生在玉米生长期间施肥灌水或降雨之后。在1998／1999和1999／2000两个作物轮作年中，土壤水分的深层渗漏损失分别为33～48mm（平均39mm）和90～92mm（平均90.7mm），分别占降水＋灌溉总量的10％和19％；淋溶到根区之下的NO3^--N量（包括来自土壤和肥料的N）分别为N12kg hm^-2（范围N6～17kg hm^-2）和N61 kg hm^-2（范围N30～84kg hm^-2），分别占施入肥料量的1．4％～4．1％和7．3％～20．3％。在玉米生长期间有较大潜力可调控灌溉与肥料用量，以提高水肥利用效率。

Soil water deep leaching and nitrate （NO3^--N） distribution in the soil profile and NO3^--N leaching losses below the root zone were investigated in fields under a local traditionally managed wheat-maize crop rotation system in the North China Plain. Coupled with the soil water balance method, soil water deep leaching and NO3^--N concentration in suction samples were determined. The results indicate that water leaching, NO3^--N distribution and leaching losses exhibited pronounced spatial and temporal variability. Events of water leaching and NO3^--N leaching loss were prone to occur during the summer maize growing season （rainy season）, after each irrigation operation and significant rainfall. Annual soil water deep leaching reached 33 - 48 mm （averaged 39 mm） in 1998/1999 cropping year and 90 - 92 mm （averaged 90.7 mm） in 1999/2000, accounting for 10% and 19% of the total amount of irrigation plus rainfall, respectively. The amount of NO3^- -N leached below the root zone （including leaching loss of soil- and fertilizer-N） averaged NO3^- -N 12 kg hm^-2 a^-1（ranging from NO3^- -N 6 to 17 kg hm^-2 a^-1） in 1998/1999 and NO3^--N 61 kg hm^-2 a^-1（ranging from NO3^--N 30 to 84 kg hm^-2 a^-1） in 1999/2000, equivalent to 1.4% - 4.1% and 7.3 % - 20.3 % of the N fertilizer applied, respectively. The results indicate that during the summer maize growing season, potentials do exist of reducing water and fertilizer inputs, so as to improve water and fertilizer use efficiency in this region.