免耕覆盖下土壤水分、团聚体稳定性及其有机碳分布对小麦产量的协同效应

【目的】基于山西运城8年（2008—2015）长期定位试验,研究免耕覆盖下土壤团聚体稳定性、团聚体活性有机碳分布特征、冬小麦水分利用效率和产量变化特征,分析土壤水分、土壤团聚体稳定性及其有机碳组分对小麦籽粒产量的协同关系,为选择适宜黄土高原旱作农业区最佳耕作模式提供理论依据。【方法】选取传统耕作秸秆翻耕还田（CT-SP）和免耕秸秆覆盖还田（NT-SM）两种耕作措施,在冬小麦收获期,利用干筛法测定土壤团聚体各粒级质量分数;测定各粒级土壤团聚体有机碳（SOC）及活性有机碳（可溶性有机碳,DOC;易氧化有机碳,EOC;微生物量碳,MBC）含量;测定土壤水分（土壤体积含水量,θ_v;播种前贮水量,SB;收获后贮水量,SA;生育期耗水量,ET;降水利用效率,PUE;水分利用效率,WUE）和作物产量等关键指标。【结果】（1）与CT-SP处理相比,NT-SM处理显著提高0.25—2 mm团聚体含量、>0.25 mm 团聚体含量（R_0.25）和几何平均直径（GMD）,分别提升13.9%、8.8%和9.6%。（2）与CT-SP处理相比,NT-SM处理中全土SOC、>2 mm和0.25—2 mm粒级团聚体SOC与MBC含量分别提升17.7%与23.6%、18.4%与18.2%和22.4%与39.2%。0.25—2 mm粒级团聚体对SOC和MBC的贡献率,分别提升18.4%和28.4%。（3）与CT-SP处理相比,NT-SM处理提高了SA、PUE、WUE和小麦产量,分别提升17.7%、8.92%、14.98%和8.92%,并且SOC、WUE、R_0.25、MWD和GMD等指标与小麦产量相关系数均达到0.9以上。（4）通过结构方程模型分析发现,土壤团聚体DOC和EOC通过协同效应影响MBC的变化,MBC含量对SOC的总效应为0.88,是影响SOC变化的主导因子。（5）土壤贮水量、土壤团聚体稳定性及其有机碳分布协同影响小麦产量,并且土壤团聚体稳定性对小麦产量表现为极显著正效应。【结论】在黄土高原旱作农业区,免耕秸秆覆盖还田可改善土壤团聚体结构,增加土壤水分含量,提高小麦水分利用效率,显著增加耕层土壤有机碳和活性有机碳组分含量,从而实现土壤固碳保墒和作物增产的协同效应。

Synergistic Effects of Soil Moisture,Aggregate Stability and Organic Carbon Distribution on Wheat Yield Under No-Tillage Practice

【Objective】Based on an 8 year (2008-2015) long-term field experiment in Yuncheng, Shanxi Province, the characteristics of stability and active organic carbon contents in soil dry aggregate, water use efficiency and winter wheat yield under no-tillage with straw mulching were studied, and the synergistic effect among soil moisture, the stability and organic carbon components of soil aggregates and wheat grain yield were analyzed, so as to provide a theoretical basis for the best tillage practice in the dry farming area of the Loess Plateau in China.【Method】In this study, two tillage treatments in the long-term field experiment were selected, including CT-SP (convention tillage with straw plowing) and NT-SM (no-tillage with straw mulching). During the winter wheat harvest period, the soil aggregate fractions were measured by dry-sieving method, the contents soil organic carbon (SOC) and active organic carbon (dissolved organic carbon, DOC; easily oxidized organic carbon, EOC; microbial biomass carbon MBC) in soil dry aggregates were determined, and soil moisture (soil volumetric water content, θ_v; soil water storage before sowing, SA; soil water storage after harvesting, SB; water consumption during growing period, ET; precipitation use efficiency, PUE; water use efficiency, WUE) and crop yield were investigated too.【Result】(1) Compared with CT-SP treatment, NT-SM treatment significantly increased the proportions of aggregate 0.25-2 mm, the contents of macro-aggregates (R_0.25) and geometric mean diameter (GMD) by 13.9%, 8.8 % and 9.6%, respectively. (2) Compared with CT-SP treatment, the contents of SOC and MBC in bulk soil, >2 mm and 0.25-2 mm in NT-SM treatment, increased by 17.7% and 23.6%, 18.4% and 18.2%, 22.4% and 39.2%, respectively. The contribution rates of 0.25-2 mm soil aggregate-associated carbons to SOC and MBC increased by 18.4% and 28.4%, respectively. (3) Compared with CT-SP treatment, NT-SM treatment increased the SA, PUE, WUE and wheat yield by 17.7%, 8.92%, 14.98% and 8.92%, respectively, and the Pearson correlation coefficients between yield and SOC, WUE, R_0.25, MWD, GMD reached above 0.9. (4) By structural equation model analysis, it was found DOC and EOC affected MBC change by a synergistic in soil aggregates, and also the total effect of MBC content on SOC was 0.88, suggesting it was the dominant factor affecting SOC change. (5) The water storage, soil aggregate stability and SOC distribution affected wheat yield by a synergistic effect. Moreover, soil aggregates stability had a significant positive effect on winter wheat yield.【Conclusion】In the dry farming area of the Loess Plateau in China, the no-tillage with straw mulching could improve the stability of soil aggregates and the soil water environment, the contents of organic carbon and active organic carbon fractions in the topsoil, and increase soil carbon sequestration, water retention and crop yield.