夏玉米不同施氮水平土壤硝态氮累积及对后茬冬小麦的影响

【目的】探讨夏玉米季不同施氮水平土壤硝态氮（NO3--N）累积及对后茬冬小麦的影响，利用作物轮作降低土壤NO3--N累积，减缓其淋洗，以提高氮肥周年利用率。【方法】夏玉米季设置不同施氮量处理，冬小麦采取节水省肥栽培，研究夏玉米收获后土壤剖面累积的NO3--N对冬小麦生长发育、产量及NO3--N累积动态的影响。【结果】夏玉米季施氮量与作物收获后土壤剖面NO3--N累积量，NO3--N累积量与冬小麦的产量都呈极显著线性正相关关系。冬小麦季采取限氮或不施氮处理作物收获后土壤剖面各层NO3--N含量，与夏玉米收获后相比都有显著降低。夏玉米季施氮240 kg?hm-2、冬小麦季施氮157.5 kg?hm-2（N240+157.5）或者冬小麦季不施氮前茬夏玉米季施氮360 kg?hm-2（N360+0）都能满足冬小麦各生育时期对氮的需求，产量、吸氮量和周年氮肥利用率相近且都保持较高的水平，但夏玉米季高施氮处理,当季氮存在很大的淋洗等损失风险。【结论】夏玉米季施入的氮肥对后茬冬小麦有很强的有效性，小麦季采取节水省肥栽培，能显著减少前茬作物收获后残留的NO3--N，减缓其淋洗，同时保障作物产量，提高氮肥利用率。生产中氮肥的合理分配应充分考虑前茬残留氮素对后茬的有效性。

Soil Nitrate N Accumulation Under Different N-Fertilizer Rates in Summer Maize and Its Residual Effects on Subsequent Winter Wheat

【Objective】 The study was conducted to clarify the annual characteristics of soil NO3--N accumulation under different N-fertilizer (NF) rates applied in maize (Zea mays L.) and its residual effects on succeeding wheat (Triticum aestivum L.) in winter wheat-summer maize rotation system.【Method】Four NF rates (0, 120, 240 and 360 kg N•hm-2) were applied in maize and the cultivation practices of water-saving and NF-saving were adopted in wheat, the annual changes of NO3--N in a 2 m-depth soil profile in different NF treatments and its residual effects on wheat were observed.【Result】There was a significant positive correlation between NF rates and residual soil NO3--N amount at maize harvest stage, and the yield of following wheat also showed a significant positive relationship with the residual soil NO3--N amount, which could be fitted by a linear model. Compared with that at maize harvest stage, NO3--N content in each soil layer sharply decreased at wheat maturity stage under the NF rates of 157.5 and zero kg N•hm-2 applied in wheat. 240 kg N•hm-2 applied in maize and 157.5 kg N•hm-2 applied in wheat (N240+157.5) or the treatment N360+0 (360 kg N•hm-2 was applied in maize but no NF in wheat) could meet wheat demand for N, eventually maintained yield, plant N uptake amount and annual apparent N recovery efficiency at a higher level. However, the treatments in which higher NF applied in maize had a great NO3--N leaching loss risk in rainy season. 【Conclusion】 NF applied in summer maize has a strong residual effectiveness to subsequent winter wheat. Adopting the water-saving and NF-saving cultivation techniques in winter wheat not only shrinks sharply the NO3--N accumulation in the soil profile, but also sustains high-yielding and increases NF recovery efficiency. Therefor, the residual effect should be considered in NF optimization in crop production.