河西绿洲灌区秸秆带状覆膜还田对土壤氮循环的影响机理

Due to the arid climate and low moisture content in Hexi oasis irrigation districts of China, the decomposition process of crop straw that is returned to farmland is slow, and eventually influence sowing of next crop. The conventional straw returning methods leads to declined productivity and reduced crop yield. Therefore, this conventional crop straw returning method has not been generally accepted by local farmers. A new crop straw returning technique was developed, in which straw is applied to blank strips with plastic film mulching and separate it from seed rows. This has overcomed the disadvantage of conventional straw returning methods. However, the mechanism of effect of returning straw to plastic mulched farmland on soil nitrogen cycling is still unclear. The project will take irrigation districts of Hexi oasis as study area, corn straw as research materials, the new straw returning method as research foundation, 15N isotope tracing micro-plot trials will carry out in long-term (28 years) and short-term (6 years) experiments, respectively, by adopting the doubly-labeled method of 15N-labeled urea and 15N-labeled corn straw, based on field observation, the collected samples will be determinated and analysed during the experimental period, the project plans to systematically study the fates of urea N and straw N, the absorption and distribution features for urea N and straw N apply at different growing stages, and the effects of soil nitrogen reserve and nitrogen cycle of straw returning in farmland ecosystem. By probeing into the mechanism of effect of returning straw on soil nitrogen cycling, the project will provide theoretical basis for extension of the new straw returning technique in Hexi oasis irrigation districts.

在我国河西绿洲灌区，由于气候干燥，还田秸秆腐解缓慢，传统全地翻压和覆盖还田会造成作物减产，本课题组的前期试验表明，“种”“还”分离的带状覆膜还田在一定程度上能避免这些弊端，但是秸秆在该还田过程中对土壤氮循环的影响机理还不清楚。为此，本项目计划以我国河西绿洲灌区为研究区域，以“种”“还”分离的带状覆膜还田为研究基础，以玉米秸秆为研究对象，在长期（28年）和短期（6年）定位试验中套布15N示踪微区试验，采用15N标记化学氮肥和15N标记秸秆的双标记方法，通过田间观测和对历史及项目期间所采样品的测定分析，研究秸秆带状覆膜还田方式下，秸秆氮和化肥氮的去向，探讨作物不同生育期对秸秆氮和化肥氮的吸收利用特点，明确长期秸秆还田对土壤氮库容量和氮素循环的影响，揭示秸秆带状覆膜还田对土壤氮循环的影响机理，为秸秆带状覆膜还田技术在河西绿洲灌区的推广提供理论依据。

项目以2011年和1988年在武威绿洲灌区设置的秸秆带状覆膜还田试验和长期秸秆还田试验为平台，结合微区试验，采用15N示踪法，系统研究了秸秆带状覆膜还田时，还田秸秆的氮素释放规律和氮素去向，化学氮肥的氮素去向；秸秆带状覆膜还田对化学氮肥追施过程中氮损失、作物产量、土壤呼吸、土壤温度、土壤水分、土壤紧实度的影响；秸秆长期还田对土壤全氮、碱解氮、土壤氮库、作物产量、作物产量稳定性、可持续性和肥料贡献率的影响；探索了不同酸度水溶肥对土壤氨挥发的影响和灌溉水酸碱度对土壤pH的影响。结果表明，在河西绿洲灌区进行玉米秸秆带状翻压还田时，还田秸秆在180天后的全氮释放率为38.99%，其中在还田前期会与作物争夺土壤氮素，在后期会释放一定氮素供作物所需；玉米在当季对还田秸秆氮素的总吸收利用率为17.35%，其中籽粒为11.81%，秸秆为5.54%，对化肥氮素的总吸收利用率为20.99%，其中籽粒为14.29%，秸秆为6.70%；玉米拔节期追肥后的氨挥发显著降低68.04%，大喇叭口期追肥后的氨挥发降低15.09%，全生育期追肥过程中的氨挥发显著降低61.25%；与不还田处理相比，土壤呼吸速率显著降低12.5％；0-10cm土壤含水量显著提高；玉米产量显著提高19.17%。玉米秸秆带状覆盖还田时，玉米在当季对还田秸秆氮素的总吸收利用率为9.52%，其中籽粒为6.47%，秸秆为3.06%；对化肥氮素的总吸收利用率为9.77%，其中籽粒为6.82%，秸秆为2.95%。玉米秸秆带状翻压覆膜还田过程中；玉米拔节期追肥后的氨挥发显著降低71.24%，大喇叭口期追肥后的氨挥发降低3.76%，全生育期追肥过程中的氨挥发显著降低61.58%；与不还田处理相比，土壤呼吸速率显著增加23.4％，0-10cm土壤含水量显著降低；玉米籽粒产量提高16.11%。灌溉溶液的酸碱度、灌水量、施氮量对土壤氨挥发的贡献率分别为31.57%、4.23%、64.2%，同时，酸性水溶肥能显著降低灌漠土土壤pH。秸秆长期还田可提高土壤全氮和碱解氮含量，秸秆连续还田31年时，较试验初始提高40.9%-50.6%和36.7%-50.5%，较不还田处理增加20.4%-28.8%和27.6%-40.5%，小麦和玉米产量显著提高142.4%和45.8%。出版专著1部，发表学术论文3篇，投稿2篇，培养硕士研究生2名，1人晋升高级职称。