华北平原玉米田能量平衡、水分利用效率和表面阻力分析

根据华北平玉米田的观测结果，分析了地表／大气能量转化传输特征。结果表明，在作物生育期内，地表能量平衡过程受下垫面特征影响很大。潜热通量是地表／大气热量交换的主要分量；玉米生长的后期有热平流输入，日平均显热通量转为负值。表面阻力在生育期早期和后期较大，而在中期较小，显示了表面阻力对地表覆盖变化和叶片衰老的响应。农田水分利用效率在生长季呈逐渐增长的趋势。

Energy balance,water use efficiency and surface resistance in a maize field

The characteristics of land surface/air energy translation was analysed on the basis of the observation data collected over a maize field in the North China Plain. The results indicated that the energy balance processes of land surface were greatly affected by the features of underlying face. Latent heat fluxes were the main component of land surface/air energy exchanges. Daily sensible heat fluxes were turned to be negative in the late growth period of maize. Among factors regulating surface energy translation, bulk canopy resistance was seasonally changed with high values in the early and late stage and with low value in the mid stage, and the lowest value of 25 s.m-1. This trend was closely related to soil cover fraction and leaf senescence condition. Water use efficiency (WUE) was not changed with evapotranspiration. The low WUE in the early stage means that the energy resources were not fully utilised, and the high WUE in the late stage means that enough soil water content was the key for high and stable yield.