农田土壤团聚体有机碳对秸秆还田响应的Meta分析

Response of farmland soil aggregate-associated organic carbon to straw return:a meta-analysis

秸秆还田是一种增加土壤有机质的有效途径,因其操作简单、经济节约而备受青睐。本文筛选了有关秸秆还田对农田土壤团聚体有机碳含量(团聚体碳)影响的35篇田间试验文献,利用Meta分析方法和随机森林模型,评估了地理位置、还田方式、还田数量及还田年限对农田土壤团聚体碳的影响效应,以期为提升土壤质量及固碳减排提供理论依据。结果表明,与不还田相比,秸秆还田总体上提高了农田土壤团聚体碳含量,这一正向效应在西南地区最高(26.5%~43.4%),华北地区最低(2.0%~10.8%),东北、西北、华东和华中地区居中。在留高茬、覆盖、深翻耕、旋耕4种秸秆还田方式中,旋耕对土壤大、小团聚体碳的增加效应最大,增幅达13.5%~18.7%;留高茬对土壤微团聚体碳的提升效应最高,约为19.5%。总体来看,秸秆还田提升土壤团聚体碳的正效应随秸秆还田量及还田年限的增加而增大,且在还田>8年后的提升效应最显著。地理区域和还田方式是影响秸秆还田条件下土壤各粒径团聚体碳的重要因素,其贡献率分别为16.2%~28.1%和8.0%~22.4%。秸秆还田提升土壤有机碳含量的物理机制是增加了土壤团聚体的物理固碳量;建议将秸秆粉碎后以旋耕方式还入土壤15 cm土层内,同时配施适量化肥(如氮肥和磷肥)增强土壤团聚体的固碳潜力。

Straw return is a practical method for effectively improving soil organic matter(SOM)and is favored owing to its simplicity and cost-effectiveness.In this study,we screened 35 relevant experimental field studies to investigate the effects of straw return on farmland soil aggregate organic carbon content.We used meta-analysis and random-forest models to evaluate the response effects of farmland soil aggregate carbon content to straw return,as well as the contribution of influential factors of farmland soil aggregate carbon content,such as geographical region,return mode,return amount,and years of straw return.This could provide a theoretical basis for enhancing soil quality and carbon sequestration,as well as for developing a reasonable aggregate carbon pool management strategy.Compared to that of the control treatment(no straw return),the carbon content of soil aggregates in China increased considerably when straw was returned to the farmlands.The positive effects of straw return on farmland soil aggregate carbon content varied remarkably across different regions in China.The highest positive effect of straw return on farmland soil aggregate carbon content was observed in Southwest China,ranging from 26.5%to 43.4%,whereas north China had the lowest positive effect of straw return on farmland soil aggregate carbon content,ranging from 2.0%to 10.8%.The beneficial impacts of straw return on farmland soil aggregate carbon content were moderate in Northeast,Northwest,East,and Central China.In addition,among the four straw return methods,including high stubble retention,mulching,rotary tillage and deep ploughing,rotary tillage had the largest influence on the rise of farmland soil large aggregate carbon content and small aggregate carbon content,ranging from 13.5%to 18.7%.High stubble retention had the highest improvement effect on farmland soil microaggregate carbon content,with a value of 19.5%.With respect to the years of straw return,the positive effects of straw return on farmland soil aggregate carbon content improved along with increasing amounts and the years of straw return.Furthermore,the beneficial effect of straw return on farmland soil aggregate carbon was most significant eight years after straw return.Additionally,the results of random-forest model showed that geographical region and straw return mode are important factors affecting farmland soil aggregate carbon with various particle sizes under the conditions of straw return,and their contribution rate was in the range of 16.2%–28.1%and 8.0%–22.4%,respectively.We also discovered that the crucial physical process by which straw return improves the organic carbon content of farmland soil on a broad scale is an increase in the physical carbon sequestration of soil aggregates.As aforementioned,it is suggested that the straw should be returned to the farmland soil within a 15 cm depth using the rotary tillage method after crushing,and simultaneously an appropriate amount of chemical fertilizer(e.g.,nitrogen and phosphorus fertilizer)should be applied to maximize the potential of soil aggregates for carbon sequestration.