Effect of Straw Incorporated to Different Location in Soil Profile on Straw Humification Coefficient and Maize Yield.

Tillage and straw incorporation were important agricultural practices that broken plough layer and improved black soil fertility. The effects of tillage and straw incorporation on straw humification coefficient, soil organic carbon (SOC), maize yield were considered in a field experiment. Subsoil combined with straw incorporation in 20~35 cm soil layer (ST+S) could break plough layer and decrease by 5.65%, 3.27% and 5.65% of bulk density compared with traditional tillage (TT), subsoil (ST) and traditional tillage combined with straw incorporation (TT+S) in six experimental years with the best effects within ST and ST+S treatments in first experimental year. The ratio of straw decomposition was faster in 0~20 cm (72.04%) than 20~35 cm (59.21%), the straw humification coefficient in 0~20 cm and 20~35 cm soil layers reached the peak in first experimental with 15.86% and 12.73%，respectively. Compared with initial soil sample, SOC and light fraction organic carbon (LFOC) of TT, ST and ST+S treatments in 0~20 cm soil layer was decreased in experimental years, but was increased by 2.94% and 12.41% within TT+S, respectively; SOC and LFOC of ST+S in 20-35 cm soil layer was increased by 9.19% and 9.93%, respectively. The effect of field treatments on maize yield showed in a decreasing trend of ST+S>TT+S>ST>TT, effects of tillage and straw incorporation on maize yield could continued to 3 years and 6 years, respectively, indicating that tillage and straw incorporation had time effect. Therefore, straw incorporated into 20~35 cm soil layer based on tillage was a effective, sustainable agricultural practice of improving black soil quality.