1. College of Resources and Environment， Jilin Agricultural University， Changchun 130118， China；
2. Key Laboratory of Straw Biology and Utilization， Ministry of Education， Changchun 130118，
China；3. Qiqihar Branch of Heilongjiang Academy of Agricultural Sciences， Qiqihar 161006， China
Abstract：In order to solve the problems of soil structural deterioration and organic carbon content decline caused by unreasonable tillage in semi-arid area of western Northeast China, the composition and stability of soil aggregates, and the distribution of organic carbon in the aggregates under different straw returning methods were studied through field positioning test to explore the effects of different straw returning methods on soil aggregate stability and organic carbon content in the semi-arid area of western Northeast China, which will provide theoretical basis and technical guidance for rational utilization of straw and soil improvement. A combination of long-term positioning test and indoor analysis was used, 6 treatments were set up , including rotation tillage (T1), straw full coverage (T2),straw semi-coverage (T3), high stubble (T4), straw crushed and mixed returning (T5) and no straw returning (ck). After autumn harvest, the undisturbed soil of the 0-20 cm plough layer was collected,
and the aggregate composition and organic carbon content were analyzed. The results showed that compared with te control treatment, among the four soil treatments of T1, T3, T4, and T5, the aggregates with a particle size of >2 000 μm had the highest content, accounting for 45%-50% of the total aggregates (P<0.05), the content of aggregates <250 μm was the smallest, accounting for only 5%-11% (P<0.05). Compared with no straw returning, the mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates with straw returning were significantly increased,and the increase in T1 treatment was the highest, and the changes of PAD and ELT values were ck>
T2>T4> T5>T3>T1. Straw returning significantly increased the content of soil organic carbon,ranging from 18.37%-65.51% (P<0.05). Except for T4 treatment, other treatments could significantly increase the organic carbon content of >2 000 μm and 2 000-500 μm fractions. The contribution rate of organic carbon in aggregates >2 000 μm to soil organic carbon was also increased,among which T1 treatment had the highest contribution rate with a value of 30%. Correlation analysis showed that soil organic carbon content was significantly positively correlated with GMD and MWD values. Suitable straw returning to the field could effectively improve the soil structure, improve the stability of soil aggregates, increase the content of soil organic carbon, and improve the contribution
rate of organic carbon from macroaggregates to soil organic carbon. Among the different returning methods, the rotation tillage method has the best effect, and is suitable for application in the semiarid area of western Northeast China.
