冬小麦-夏玉米轮作体系秸秆深还田的固碳减排效应及其机制研究

Straw incorporation can improve soil structure, promote soil carbon (C) sequestration, and improve soil fertility and resource use efficiency. However, the traditional straw incorporation methods (e.g. mulching or shallow incorporation) raised a lot of problems, such as seedling emergence and nitrogen (N) competition. These problems restrict the further optimization and promotion of the straw incorporation technology. Straw deep incorporation, namely that crop residues are incorporated into 20-38 cm soil depth, will effectively prevent the over-accumulation of straw at the soil surface and N competition with succeeding crops. Meanwhile, it may also improve soil fertility at subsoil. However, due to specific conditions at subsoil (e.g. low oxygen concentration, high water content, low nutrient contents, low microbial diversity and activity), it remains unknown whether straw deep incorporation will contribute to soil carbon C or N sequestration, and whether the practice will affect crop yields and greenhouse gas (GHG) emissions. This project aims to clarify the effects of straw deep incorporation on the growth and yield of succeeding crops, soil C and N sequestration, GHG emissions in the winter wheat-summer maize rotation system. We plan to conduct this study using the established straw deep incorporation technique, static chamber-gas chromatography, 13C and 15N stable isotope techniques. Zymography and high-throughput sequencing techniques will also be used to estimate the enzymatic and microbiological mechanisms. These results will be of importance to optimize the regional straw incorporation method, improve straw management, and provide theoretical and technical supports for agricultural green development.

秸秆还田能够改善土壤结构，促进农田固碳，有助于培肥地力，实现资源的高效利用。然而覆盖还田、耕层还田等传统秸秆还田方式不利于下茬作物的播种出苗，存在与作物争氮等问题，制约了技术的进一步优化与推广。秸秆深还田（埋深20-38cm）可有效避免土壤表层秸秆堆积，提高下茬作物播种出苗质量、降低氮素竞争。然而，深层土壤中氧气浓度低、水分含量高、养分缺乏、微生物多样性和活性低，秸秆深还田是否有助于农田固碳（氮），是否影响作物产量和温室气体排放等问题尚需进一步研究。本项目采用田间定位研究方法，应用静态箱-气相色谱法、13C和15N稳定同位素示踪技术、原位酶谱技术和高通量测序等技术手段，明确玉米秸秆深还田对冬小麦-夏玉米轮作系统作物生长、土壤固碳、温室气体排放动态及秸秆碳氮去向的影响，阐明其酶学和微生物学调控机制。研究结果将为优化秸秆还田方式，促进秸秆还田利用，培肥地力，实现农业绿色发展提供理论支撑。

耕地质量提升是国家“藏粮于地”战略的核心，也是维持我国粮食安全的重要保障。秸秆还田是土壤培肥的有效方法，可以改善土壤结构，实现农田土壤肥力提升。明确秸秆还田对土壤养分循环及作物生产的影响，将为区域农业绿色可持续发展提供理论和技术支撑。传统的秸秆还田方式存在对土壤扰动大、秸秆无法连年大量还田等问题。本研究设置秸秆不还田（SR），秸秆覆盖还田（SM）、秸秆浅旋还田（SI）、秸秆深翻还田（DP-SI）和秸秆集中深还田（DI-SI）5个处理。探究不同秸秆还田方式下的农田生产力（土壤养分、有机碳、作物产量）以及土壤生态（微生物、酶、温室气体排放），为明确秸秆集中深还田模式的特点、推动秸秆集中深还田发展提供理论基础。经过两年的试验，研究取得以下进展：不同秸秆还田管理措施对土壤养分含量、温室气体排放速率、碳氮磷循环酶活性和微生物群落有显著的影响。秸秆深还田对表土的改良作用有限，小麦季时表土含水量、铵态氮含量和全氮含量甚至处于较低水平；但其显著提高了底土养分含量，小麦季时整个生育期硝态氮含量提高了50%-215%，铵态氮含量高了49%-76%，速效磷含量高了32%-85%，玉米季时也是如此。相比其他处理，秸秆深还田处理的小麦和玉米产量也是最高的，分别达到8.58 t ha-1和13.04 t ha-1。秸秆深还田不会降低小麦或玉米生育期内的CO2累计排放量，但降低了土壤N2O排放，小麦季和玉米季时，累计排放量分别只有162 mg m-2，1808 mg m-2。秸秆深还田也显著提高了底土碳氮磷循环酶活性，降低了底土细菌群落α多样性。总之秸秆深还田可以提高底土养分含量和循环酶活性，有助于实现底土的培肥，同时在提高作物产量方面有较大潜力。秸秆深还田对土壤环境和微生物群落的改善也减少了N2O的排放，为农田减排提供了新的可靠途径。