秸秆还田量对陇中旱作麦田土壤团聚体稳定性和有机碳含量的影响

为探明秸秆还田后土壤团聚体与有机碳的变化特征和作用机制，依托2019年布设于甘肃省定西市李家堡镇的不同秸秆还田试验，设置两种秸秆类型：小麦秸秆和玉米秸秆，秸秆还田量分别为：0（CK）、3 500（低量）、7 000（中量）、14 000 kg·hm^-2（高量）,研究了秸秆还田对陇中黄土高原旱作农田土壤团聚体稳定性和有机碳的影响。结果表明：土壤机械稳定性团聚体以>0.25 mm团聚体为主，且随土层加深粒径逐渐增大，水稳性团聚体均与之相反；秸秆还田较不还田处理的机械稳定性和水稳性<0.25 mm粒级团聚体含量分别降低了3.53%～21.74%和2.73%～8.95%,土壤机械稳定性和水稳性团聚体平均重量直径MWD、几何平均直径GMD的提升幅度最大分别达到16.29%、30.12%和20.93%、12.12%,团聚体破碎率PAD降低了2.53%～13.23%,在中量秸秆还田时效果最好，且玉米秸秆比小麦秸秆效果更明显。秸秆还田提升了土壤有机碳含量，且在表层土壤秸秆还田量越高，对土壤有机碳的提升效果越显著，其中玉米秸秆高量还田处理的土壤有机碳含量较CK显著提高了...

Effects of straw returning amount on stability of soil aggregates and organic carbon content in dryland wheat field of the Loess Plateau

This study aimed to investigate the effects of straw returning on stability of soil aggregates and organic carbon in the dry farmland of the Loess Plateau in central Gansu. Different straw returning experiments were conducted in Lijiapu Town, Dingxi City, Gansu Province in 2019. The two straw types were wheat and corn, and the straw returning amount included 0 (CK), 3 500 kg·hm^-2 (low amount), 7 000 kg·hm^-2 (medium amount) and 14 000 kg·hm^-2 (high amount). The results showed that soil mechanically stable aggregates were >0.25 mm aggregates as the main aggregates, and the particle size gradually increased with the deepening of soil layer, while that of water\|stable aggregates were the opposite. When compared the treatment of straw returning to the field with no returning to the field, the contents of <0.25 mm mechanical stability and water stability aggregates decreased by 3.53%~21.74% and 2.73%~8.95%, respectively. The average weight diameter MWD and geometric average diameter GMD of soil mechanical stability aggregates increased by 16.29% and 30.12%, respectively, while that of water stability aggregates increased by 20.93% and 12.12%, respectively. The aggregate fragmentation rate PAD decreased by 2.53%~13.23%. The effect of medium straw was the best, and the effect of corn straw was more significant than that of wheat straw. Straw returning increased soil organic carbon content, and the higher the amount of straw returning on the soil surface, the more significant the improvement effect on soil organic carbon became. Compared with CK, the soil organic carbon content in high amount of corn straw returning to the field was significantly increased by 31.37%. In the subsoil, the medium wheat straw returning and high corn straw returning significantly increased soil organic carbon content by 29.85% and 36.31%, respectively, when compared with CK. The results of correlation and multiple regression analysis showed that soil organic carbon had a significant positive correlation with the stability index of mechanically stable aggregates, and extremely significant positive correlation with the stability index of water\|stable aggregates. However, there was an extremely significant negative correlation between aggregate fragmentation rate and soil organic carbon. The fitting equation of soil organic carbon and water\|stable aggregate GMD was the most suitable to describe the relationship between soil organic carbon and the stability of soil aggregates. In conclusion, the optimum amount of corn straw returning was 7 000 kg·hm^-2 for effectively improving the structure of soil aggregates, soil carbon sequestration potential and soil quality.