Effects Of Straw Returning Methods On Black Soil Organic Matter

Recently, quantity and quality of soil organic matter in black soil region of northeast China has declined rapidly, which is detrimental to crop production and soil quality. Facing some problems such as the immaturity of straw returning technology and the ambiguity of its carbon sequestration, this study considered three research sites(1-different ways of straw returning test in Qinggang county of Heilongjiang province, 2-different amount of straw returning in Gongzhuling city of Jilin province, 3-National Black Soil Fertility and Fertilizer Effects Long-term Monitoring Network in Gongzhuling city of Jilin province) in black soil region as the platform, and systematically analyzed the influence of different amount, ways and tillage measures of straw returning on organic matter of black soil by combining field monitoring experiments and DNDC(Denitrification-Decomposition) model. The results of this study would provide technological support to improve the black soil organic matter content, and also supply theoretical foundation for researching black soil carbon cycling and balanced process of straw returning. The main results were as follows:(1) Results of different ways of straw returning showed that both soil organic carbon content and soil total nitrogen content had no significant difference between straw buried and straw mulching. Returning 100%, 50% and 33% of straw yields could increase soil organic carbon by 16.56%、5.06% and 4.92% respectively, and long-term straw returning could improve soil organic carbon content by 23.74%.(2) Straw returning could significantly increase soil respiration rate and carbon emissions. To sum up all the results of the three experiment sites, sensitivity of soil respiration rate on soil temperature and moisture were different under different treatments. As a whole, the soil respiration rate had a relatively larger impact on soil temperature, and 26%~79% variation of soil respiration could be explained by soil temperature.(3) Straw returning could improve soil activity carbon composition and enzyme activity. Test results of different returning ways displayed that straw buried returning could increase soil readily oxide organic carbon by 47.20% compared with straw mulching. Compared with 33% of straw yields returning, 100% and 50% straw returning could enhance soil particulate organic carbon by 54.33% and 42.45% respectively.(4) Based on the long-term field monitoring data from 1990 to 2012, the applicability of DNDC model in black soil was identified. The relative parameters such as mean absolute error(MAE), relative root mean square error(RMSE) and the determination coefficient(R2) showed a good fitting degree between simulated data and observed data, which also indicated that the model could be used to simulate the changing tendency of black soil organic carbon in northeast China. The predicted result of soil organic carbon, which was under different managements based on future climate scenarios(1990-2050), displayed that both no fertilizer and NPK treatments would result in the decrease of soil organic carbon, while combining manure with chemical fertilization or straw could significantly increase soil organic carbon content. Under any nitrogen application level, crop yield would increase with the increase of soil organic carbon content, and the improvement of crop yield under lower nitrogen application was relatively larger compared with higher nitrogen application.