Simulation of accumulation and mineralization (CO2 release) of organic carbon in chernozem under different straw return ways after corn harvesting

Straw return is the main way of fertility improvement of cultivated chernozem in Songnen Plain of Northeast China. To reveal the effect of corn straw return mixed with soil or ploughing (straw mixing for short) and corn straw return to the surface of soil (straw mulching for short) on fertility and environment of soil, we focused on the effects of different straw applications on the release of CO2 and accumulation of soil organic carbon. A laboratory simulative incubation experiment was conducted with chernozem, and corn stalk. Under the constant condition of 28 degrees C, all curves of the emission rate of CO2 had appeared a peak of the emission of CO2 on the 4th or 6th day of the culture, and then stepped into the first slow emission platform on the 13th-52nd day and stepped into the second slow emission platform on the 52nd-91st day. With the same amount of straw, the peak value of CO2 emission rate of straw mixing (23.00, 43.64, 79.70 mg kg(-1) d(-1) for straw 2%, 4%, and 6%, respectively) was apparently greater than that of straw mulching (22.94, 39.76, 58.71 mg kg(-1) d(-1) for straw 2%, 4%, and 6%, respectively). However, after entering the slow emission platform, the average emission rate of CO2 of straw mixing would be less than that of straw mulching. There was an apparent intersection point (about 31 d for straw 2%, 4% and 47 d for straw 6%) on the curves of both the CO2 emission rate of straw mixing and straw mulching. Before the intersection point, the accumulated amount of CO2-C emission of straw mixing was greater than that of straw mulching and then lower than that of straw mulching gradually after the point. The analysis of the result about the soil organic carbon and the composition of micro-aggregate showed that with the same amount of straw addition, straw mixing could increase soil organic content and improve the composition of micro-aggregate better than straw mulching. The results indicated that it might have a better effect on fertility and environment of soil than the return of straw for surface of soil if the means of ploughing in autumn and rotary tillage, etc. could be used in the process of the returning of straw mixed with soil or cultivation. (C) 2015 Elsevier B.V. All rights reserved.