黄土高原南部夏季不施肥种植玉米对旱地土壤残留养分的利用

夏季降水是造成我国西北黄土高原区旱地土壤硝态氮淋溶的主要原因。通过田间长期定位试验研究了冬小麦收获后，不施肥种植夏玉米而利用土壤残留养分阻止硝态氮淋溶的效应。结果表明，小麦播前施氮量增加，夏玉米收获期生物量和子粒产量增加，但磷肥用量增加对其影响不明显。小麦播前施氮量增加，夏玉米氮磷钾累积增加，施磷量增加，氮钾素累积降低，磷素累积无显著变化。土壤剖面含水量随小麦播前施氮量增加而降低，不同施磷量土壤剖面水分累积量的差异显著减少。不施肥种植夏玉米可以有效阻止和减少土壤剖面硝态氮淋溶，但在小麦播前施氮240和320kg·hm^-2时仍有较明显淋溶，其累积峰逐渐向深层土壤转移，造成氮素损失。施磷时，土壤剖面0-220cm硝态氮累积量下降，220cm以下土层变化不明显。

Utilization of Residual Nutrients in Soil by Summer Maize Cropping with No Fertilization in Southern Area of the Loess Plateau

It is the rainfall that is the main reason for nitrate leaching in dryland soil in the southern area of the Loess Plateau. A long-term field experiment with the rotation of winter wheat and summer maize was initiated in 2004, and the N and P fertilizer were applied before winter wheat seeding, summer maize was seeded with no fertilizer added to study how the crop utilize residual nutrient in soil and prevent nitrate leaching under no fertilization condition. The result showed that the biomass and grain yield of summer maize increased with the increase of N rates applied before wheat seeding, but the increase of P rates had no effect on them. N, P and K uptake of summer maize increased with N rates. However, N and K uptake of summer maize decreased, and P uptake had no significant changes with P rate increasing. The amount of water in soil profile decreased with the increase of N rates before winter wheat seeding, while the difference of soil water at different soil layers decreased significantly over P rates. In conclusion, summer maize cropping with no fertilization effectively stopped and decreased soil nitrate leaching, but when too much N, such as 240 and 320 kg N ·hm^-2 of N fertilizer was used before winter wheat seeding, the nitrate could still be leached down to very deep soil layers, the nitrate leaching peak was obviously moving down to deep layers, and this might result in N loss finally. Nitrate accumulation in 0-220 cm soil layers decreased at different P rates applied before wheat seeding, and it had no significant changes for that in 220 cm to 300 cm layers.