湖南双季稻田氮素去向及残效定量研究

【目的】研究不同施氮量下双季稻田氮素的吸收利用、损失残留和残效特征，定量化揭示湖南双季稻田肥料氮去向和残效规律，为制定科学合理的双季稻田氮肥施用措施提供理论依据。【方法】于2017—2018年在湖南双季稻区开展田间15N微区试验，按氮肥施用量设4个施氮量（以纯N计）处理:N0（不施氮）、N1（早晚稻均为90 kg/ha）、N2（早稻120 kg/ha，晚稻135 kg/ha）、N3（早稻150 kg/ha，晚稻180 kg/ha）。2017年施用15N标记尿素，研究各处理的15N吸收利用、15N在土壤中的残留及15N损失率，明确肥料15N的不同去向及其占比；2018年施用等量未标记尿素，分析各处理残留15N的吸收利用和损失率。【结果】差减法氮肥吸收利用率随施氮量的增加而显著下降（P< 0.05），2017年早晚稻氮肥吸收利用率分别为42.14%～46.62%和35.45%～43.08%，2018年分别为37.93%～42.56%和37.20%～44.51%。示踪法2017年早稻15N回收率为24.49%～24.53%；晚稻15N回收率为25.32%～26.59%，晚稻略高于早稻；各处理15N回收率相近，无显著差异（P> 0.05）。各处理肥料15N去向基本一致，作物吸收、土壤残留和总损失分别约占25%、23%和52%。肥料15N主要残留在0～20 cm土层中，约占总残留量的77%，20～40 cm土层约占19%，40～60 cm土层约占4%。上一季水稻残留的氮肥，可供下一季水稻吸收利用，是土壤氮库的补充，0～20 cm土层残效最好，2018年两季水稻累积残留15N吸收率为8.13%～9.28%，累积损失率为38.68%～52.97%，最终残留率为38.90%～52.05%。【结论】双季稻田氮肥利用率较低，氮肥损失占比较大，早晚稻均达50%以上；水稻积累的氮素主要来自于土壤，土壤氮贡献率达71.00%以上。双季稻生产中应充分考虑土壤自身的供氮能力以及上季水稻的氮肥残效，适当降低当季水稻的施氮量，实现氮肥的高效利用。

Quantitative study on nitrogen fate and residual effect of double cropping rice fields in Hunan

【Objective】The purpose of this paper was to study the characteristics of nitrogen absorption, utilization, loss and residual effect of double cropping rice fields under different nitrogen applications, and the fertilizer nitrogen direction and residual effect rule of double cropping rice fields in Hunan were quantified, providing theoretical basis for the establishment of scientific and reasonable nitrogen fertilizer management measures in double cropping rice fields.【Method】This study conducted a 15N micro-plot experiment in Hunan double cropping rice area in 2017-2018, set four treatments:N0(no nitrogen fertilizer), N1(with nitrogen fertilizer 90 kg/ha in both early rice and late rice), N2(120 kg/ha of nitrogen fertilizer in early rice, 135 kg/ha of nitrogen fertilizer in late rice) and N3(150 kg/ha of nitrogen fertilizer in early rice, 180 kg/ha of nitrogen fertilizer in late rice) according to the N application level(based on pure N). 15N labeling-urea was applied in 2017, the absorption and utilization of 15N, the residue of 15N in the soil and the loss rate of 15N in each treatment were studied, and the different directions and proportions of fertilizer 15N were determined., the same amount of unlabeled urea was applied in 2018, analyzing the absorption and utilization of residual 15N, the total loss rate of residual 15N in each treatment.【Result】The results of difference subtraction method showed that the nitrogen absorption use efficiency decreased significantly with the increase of nitrogen application(P< 0.05).In 2017, the nitrogen absorption use efficiencies of early and late rice were 42.14%-46.62% and 35.45%-43.08%, respectively, 37.93%-42.56% and 37.20%-44.51% in 2018.The 15N tracer method results showed that in 2017, the 15N recovery rate of early rice under different treatments was 24.49%-24.53%, and late rice was 25.32%-26.59%, late rice was slightly higher than early rice.The 15N recovery rate of all treatments was similar, with no significant difference(P> 0.05).The direction of 15N fertilizer in each treatment was basically the same, the crop absorption, soil residues and total losses accounted for about 25%, 23% and 52%, respectively.Fertilizer 15N mainly remained in the 0-20 cm soil layer, accounting for about 77% of the total residual amount, about 19% in the 20-40 cm soil layer, and about 4% in the 40-60 cm soil layer.The residual fertilizer nitrogen from the last rice season could be absorbed and utilized by the next rice season, which became the supplement of soil nitrogen pool.The residual N in the soil at 0-20 cm had the best residual effect.In 2018, the cumulative absorption rate of the residual 15N in early rice and late rice was 8.13%-9.28%, the cumulative loss rate was 38.68%-52.97%, and the final residual rate was 38.90%-52.05%.【Conclusion】The nitrogen fertilizer use efficiency of double-cropping rice field is low, and nitrogen fertilizer loss accounted for more than 50% in both early rice and late rice;nitrogen accumulation in rice mainly comes from soil, and the contribution rate of soil nitrogen is more than 71.00%.In the production of double cropping rice, the nitrogen supply capacity of the soil itself and the fertilizer residue of rice in the last season should be fully considered, and then the amount of nitrogen applied in the current season should be reduced appropriately to achieve the high utilization of nitrogen fertilizer.