稻-麦轮作体系中有机氮与无机氮的去向研究

【目的】在中国多熟制农作生态系统条件下,农田中氮素的低有效度是阻碍作物高产和导致环境问题的重要因素。本项研究旨在跟踪稻麦轮作体系中化学氮肥与有机作物残茬(专指作物地上部秸秆)的氮素去向,为农田氮素的可持续管理提供理论依据。【方法】采用随机区组设计的田间多重复小区内设置15N同位素示踪微区的连续跟踪试验的方法。【结果】在施用化学氮肥的基础上无论作物残茬是取出还是还田,肥料对作物吸氮的贡献率为17.17%(16.55%—17.79%),而施用作物残茬的相应值为12.01%,即作物吸氮有82.83%或87.99%来源于土壤氮库。化学氮肥和作物残茬的作物氮素回收显示截然不同的模式:作物对化肥氮的回收呈现一次性特征,即施肥后第1季的氮回收量占到总回收氮量的92.04%,与之相应单施作物残茬区的第1季作物15N回收率为总回收率的38.03%。表明化肥氮绝大部分在第1季为作物回收,作物残茬氮则有较长的后效;第1季结束时,化学氮肥区和作物残茬区的土壤15N残留率分别为33.46%(两种残茬管理方式的平均值)和85.64%。残茬氮的土壤残留远远高于化肥氮的残留率;在第6季(化学氮肥区)或第5季(作物残茬区)结束时,化肥区与残茬区的作物+土壤的总15N回收率有显著差异(分别为64.38%和79.11%),而在施用化学氮肥的基础上加入或不加作物残茬对肥料氮的作物+土壤回收率则影响很小。【结论】化学肥料氮与作物残茬氮相比,前者对作物吸氮而言更为快速有效。而与之相反,作物残茬氮则对提高土壤供氮能力有更多贡献,因为作物残茬氮进入土壤有机质库的量高于化肥氮。为此,在农业生产中应实行化学氮肥与有机氮源的合理配合使用。

Fate of Nitrogen-15 from Organic and Inorganic Sources in Rice-Wheat Rotation Cropping System

Objective]Among the various factors that affect crop yield, N availability is one of the most important limiting factors impeding crop yield increase.Method]In this study, the recovery of a single application of ~(15)N-labeled fertilizer or residues in rice-wheat cropping system was determined for up to 5/6 consecutive growing seasons.The crop residues from the previous season were either incorporated or removed as two different treatments.Result]Results showed that, on average, 17.17% (16.55%-17.79%)of crop-N was derived from N fertilizer during the first growing season, suggesting that approximately 80% of crop N was not directly from the N fertilizer.When 15N-labeled residues were applied, 4.48% of the crop-N was derived from residues in the first growing season.Soil organic matter N contributed 82.83% of the N in the crop when 15N-fertilizer was applied or 87.99% when organic residues were applied.The average recovery of fertilizer-N and residue-N in the soil after the Fwst growing season was 33.46% and 85.64%, respectively.There was a larger difference in the total tSN recovery in plant and soil when N was applied as fertilizer or residues.Incorporation of crop residues following the ~(15)N-fertilizer application did not significantly promote ~(15)N recovery in the crop or soil.On average, only additional 1.46% of N for the fertilizer-applied field or 5.97% of N in the residue-applied field was recovered by the crops during the 2nd and 3rd growing season.After 6 growing seasons, the total recoveries of ~(15)N in crop and soil were approximately 64.38% for fertilizer-applied field and 79.11% for residue-applied field.Although fertilizer-N appeared to be more readily available to crops than residue-N, residue-N replenished soil N pool, especially N in soil organic matter, much more than fertilizer-N after 6 growing seasons.Therefore, residue-N is a better source for sustaining soil organic matter N content.Conclusion]Results of experiment suggest that the long-term effects of fertilizer or residues in the crop and soil are different.However, there was a little difference between the practices of residue incorporation and residue removal following the N fertilizer application.