Decomposition regularity of organic materials in Sanjiang Plain region

Net bag method was used to determine the decomposition characteristics of soybean and maize stalks under two approaches of returning crop residues into soils. The results show that after 150 days of composting, residual rates of maize and soybean stalks are between 33.7%~61.1% under the two treatments. The order of decomposition rate of the stalks is: soil-covered treatment > open-air treatment, soil-covered maize stalk > soil-covered soybean stalk. Decomposition regularities of soybean and maize stalks in open-air are almost the same. As for the cell structure, with the time of treatments, tissues become blurred and loose, parenchyma and vascular bundles break-down, and intracellular matters disappear in maize stalk. However, there is no significant change in tissue structures of soybean stalk. Organic carbon decomposition rates of different organic materials are respectively 39.9%~48.9% and 49.6%~65.8% under open-air and soil-covered treatments. Stalk decomposition rates under soil-covered treatments are higher than open-air treatments. Decomposition rates of total N and K are respectively 51.1%~67.7% and 74.6%~91.7%. For maize, the decomposition rates of total P are respectively 49.4% and 56.7% higher than soybean under open-air and soil-covered treatments. With regard to material returned to the soil, maize stalk is superior to soybean stalk.