施氮水平与模拟降雨pH值对玉米冠层NO3--N淋失的影响

为探明降雨特别是酸雨对玉米冠层氮素淋失的影响，以盆栽试验春玉米为指示作物，采用自制人工降雨器进行模拟降雨，研究施氮与不施氮（对照）条件下玉米冠层NO3--N淋失动态、数量及随生育期和降雨酸度的变化规律。结果表明，中性和弱酸性降雨淋洗，NO3--N淋失量主要由冠层氮素含量决定，而强酸雨淋洗，NO3--N淋失量受降雨pH值和冠层氮素含量共同影响。各生育期玉米冠层NO3--N淋失量随降雨pH值降低变化规律不一，生育前期降雨pH值对冠层NO3--N淋失影响较生育后期显著，在研究降雨酸度对玉米冠层NO3--N淋失的影响时，必须考虑生育期。相同pH值模拟降雨条件下，玉米冠层NO3--N淋失量随生育期推进逐渐降低：11叶期>吐丝期>灌浆期，生育前期显著高于中后期。玉米冠层NO3--N淋失量不仅与介质施氮有关，同时受降雨pH值影响，2因素在不同生育期对NO3--N淋失贡献大小有所不同，但总体看，植物体氮素丰富程度是影响冠层NO3--N淋失的主要因素。各生育期玉米冠层均存在一定数量的NO3--N淋失，尤以生育前期为甚，说明在研究农田生态系统氮素流量和冠层氮素损失时，冠层氮素淋失应予以考虑。

Effects of N application and simulated rainfall pH value on NO3-N leaching loss from canopy of maize

In order to find out the effect of acid rain on corn canopy, a simulated rainfall experiment was conducted to investigate the influence of N application and rainfall pH on nitrate leaching loss from the potted maize canopy as well as its changes over the growing season. The results showed that the amount of nitrate (NO3--N) leaching from maize canopy was mainly influenced by canopy N content which closely related with N application when rainfall pH was above 5.0. N application significantly increased the amount of canopy NO3--N leaching loss, nevertheless, when rainfall pH was 4.0, both rainfall pH and canopy N content had significant influence on NO3--N leaching loss. The change characteristics of NO3--N leaching loss with decreasing rainfall pH varied at different growth stages, rainfall pH had more significant influence on NO3--N leaching in early growth stage than in later growth stage. Under the same pH rainfall condition, the amount of canopy NO3--N leaching loss decreased with maize growing: 11-leaf period >spinning period > grain-filling period, and the amount of leaching loss in early growth stage was obviously higher than in later stage. In conclusion, both canopy N content and rainfall pH could influence NO3--N leaching loss, but the canopy N content was the comparatively main factor, the maize canopy NO3--N could be significantly leached by simulated rainfall, especially in early growth stage, thus the amount of NO3--N leaching from canopy should be taken into account in study of canopy N cycle, flux and losses.