Effect of different straw return years on humus composition of soil

The decrease of the soil organic matter content has the influence on the soil productivity. This article is studied the composition of straw application on soil humus with different fixed number of years of deep straw return.The results shows that both the second year and third year of straw return, the content of organic(SOC) is basically the same in the surface, but the content of SOC in subsurface, the third years is higher than the second year. The organic carbon content of the various components of soil humus are 0- 20 cm greater than 20- 40 cm,but with the increasing of straw return rate, this gap is becoming decreasing and at last the content is 20- 40 cm greater than 0-20 cm. Compared with the third year and second year, the content of FA decreased, while the content of HA, Hu and PQ increase. It means that after three years straw return, the content of most organic carbon increase and the soil humification increases. The research has the guiding significance for improving soil organic matter content and soil fertility.