Impacts of straw, biogas slurry, manure and mineral fertilizer applications on several biochemical properties and crop yield in a wheat-maize cropping system

To investigate the effects of different sources of organic matter on soil biochemical properties and crop productivity and to find the best substitute for cow manure in the fields, a field experiment was carried out in a wheat-maize cropping system during 2012-2015. Three types of fertilizer applications, including a mineral fertilizer (CK), straw (S) and biogas slurry (B) were compared with cow manure (M) under an equal dose of nitrogen. In the 0-20 cm soil layer, the soil total nitrogen, microbial biomass nitrogen and carbon content of the M treatment was the highest, and the total organic carbon equivalent ratio of M decreased by 28.60% respectively, relative to S. Compared with CK, S and B, the urease activity equivalent ratio in the M treatment increased by 52, 12 and 21%, and the invertase activity equivalent ratio increased by 21, 20 and 26%, respectively. There were no significant differences in the hydrogen peroxidase activity among the four treatments. The annual crop yield and water use efficiency of the M treatment was significantly higher than other treatments, followed by S, B and CK. Our findings indicated that straw returning was the best substitute for cow manure.