玉/豆和玉/薯模式下氮肥运筹对玉米氮素利用和土壤硝态氮残留的影响

过量施用氮肥造成的环境问题日益严重，氮肥合理使用已成为人们研究的热点.本文研究了西南玉米两种主要套作模式下氮肥运筹对玉米氮素利用和土壤硝态氮残留的影响.结果表明：连续分带轮作种植玉/豆模式后，玉米收获期植株中的氮素积累较玉/薯模式平均提高了6.1%，氮收获指数增加了5.4%，最终使氮肥利用效率提高4.3%，氮素同化量提高了15.1%，氮肥偏生产力提高了22.6%；玉米收获后硝态氮淋溶损失减少，60～120 cm土层中硝态氮残留玉/豆模式较玉/薯模式降低了10.3%，而0～60 cm土层中平均提高了12.9%，有利于培肥地力，两年产量平均较玉/薯模式高1249 kg·hm^-2，增产22%；增加施氮量提高了植株氮素积累，降低了氮肥利用率，显著提高了表层土壤中硝态氮的累积，60～100 cm土层中硝态氮的累积量在0～270 kg·hm^-2处理间差异不显著，继续增加施氮量会显著增加土壤硝态氮的淋溶；氮肥后移显著提高了土壤0～60 cm土层硝态氮的积累.两种模式下施氮量和底追比对玉米氮素吸收和硝态氮残留的影响结果不一致，玉/豆模式以施氮180～270 kg·hm^-2、按底肥∶拔节肥∶穗肥=3∶2∶5的施肥方式有利于提高玉米植株后期氮素积累、氮收获指数和氮肥利用效率，减少了氮肥损失，两年最高产量平均可达7757 kg·hm^-2；而玉/薯模式在180 kg·hm^-2、按底肥∶穗肥=5∶5的施肥方式下，氮素积累利用及产量均优于其他处理，两年平均产量为6572 kg·hm^-2，可实现两种模式下玉米高产、高效、安全的氮肥管理体系.

Effects of nitrogen management on maize nitrogen utilization and residual nitrate nitrogen in soil under maize/soybean and maize/sweet potato relay strip intercropping systems.

A large amount of nitrogen (N) fertilizers poured into the fields severely pollute the environment. Reasonable application of N fertilizer has always been the research hotpot. The effects of N management on maize N utilization and residual nitrate N in soil under maize/soybean and maize/sweet potato relay strip intercropping systems were reported in a field experiment in southwest China. It was found that maize N accumulation, N harvest index, N absorption efficiency, N contribution proportion after the anthesis stage in maize/soybean relay strip intercropping were increased by 6.1%, 5.4%, 4.3%, and 15.1% than under maize/sweet potato with an increase of 22.6% for maize yield after sustainable growing of maize/soybean intercropping system. Nitrate N accumulation in the 0-60 cm soil layer was 12.9% higher under maize/soybean intercropping than under maize/sweet potato intercropping. However, nitrate N concentration in the 60-120 cm soil layer when intercropped with soybean decreased by 10.3% than when intercropped with sweet potato, indicating a decrease of N leaching loss. Increasing of N application rate enhanced N accumulation of maize and decreased N use efficiency and significantly increased nitrate concentration in the soil profile except in the 60-100 cm soil layer, where no significant difference was observed with nitrogen application rate at 0 to 270 kg·hm^-2. Further application of N fertilizer significantly enhanced nitrate leaching loss. Postponing N application increased nitrate accumulation in the 60-100 cm soil layer. The results suggested that N application rates and ratio of base to top dressing had different influences on maize N concentration and nitrate N between maize/soybean and maize/sweet potato intercropping. Maize N concentration in the late growing stage, N harvest index and N use efficiency under maize/soybean intercropping increased (with N application rate at 180-270 kg·hm^-2 and ratio of base to top dressing = 3:2:5) and decreased nitrate leaching loss with yield reaching 7757 kg·hm^-2 on average. However, for maize/sweet potato, N concentration and use efficiency and maize yield increased significantly with N application rate at 180 kg·hm-2 and ratio of base to top dressing=5:5 than that under other treatments with yield reaching 6572 kg·hm^-2. Under these circumstances, it would be possible to realize maize high yield, high efficiency and safety of N management under maize/soybean and maize/sweet potato relay strip intercropping systems.