中文摘要：

为了进一步明确黄土高原半干旱区覆膜农田氮素循环变化动态及其机理，以夏玉米为研究对象，采用大田试验研究了覆膜管理对植株氮素（全氮）和土壤氮素（无机氮、全氮）变化动态的影响。试验结果表明：1）覆膜和不覆膜处理土壤NO3^--N含量随玉米生育期的推进表现出近似斜“N”的变化规律。2）相对于不覆膜处理而言，覆膜处理地上部分氮素积累量表现出倒“V”型变化趋势。成熟期不覆膜处理茎叶中氮素残留较多，即将氮素更多地用于营养生长；而覆膜能使植株吸收的氮素更多地转移到籽粒中去，更多地用于生殖生长。3）对于不同土壤剖面不覆膜处理土壤全氮含量而言，覆膜处理随玉米生育期的推进表现出相似的“W”型变化规律。且随土壤深度增加，变化规律有所延迟。三叶期至拔节期由于植物根系长度限制出现下降趋势；拔节期至籽粒形成期，由于覆膜能够改善土壤水热状况进而影响土壤中氮素分布，故出现上升趋势；籽粒形成期至成熟期变化规律与植物地上部分总氮含量恰好相反，说明该阶段土壤中全氮变化与玉米的生长状况密切相关。根据本研究结果，覆膜对玉米生育前期土壤氮素变化影响较大，生育后期土壤氮素变化主要与玉米生长状况密切相关，且覆膜有助于提高玉米的产量和营养品质。

英文摘要：

Plastic mulch is often used in maize production systems on the Loess Plateau.The effect of plastic mulch on plant and soil nitrogen (N)(inorganic and total N)of maize in semi-arid farmland was investigated in a field experiment.There were two mulching treatments;mulching and no mulching.No fertilizer N was ap-plied to any plots.The trial was a randomized block design with 3 replicates.The results showed that:1)Soil NO3 --N increased as the season progressed with little mulch effect on seasonal variation.2)No mulching re-sulted in more N allocated to the vegetative organs at physiological maturity compared to mulched,whereas the mulched treatment resulted in more N being transferred from the vegetative organs to the grains during the grain filling period.3 )Mulching increased soil moisture.During the grain filling period the total N content of the aerial parts of the plants were closely related to soil N status.It is concluded that mulching significantly im-proved the yield and nutritional quality of maize.