Changes in soil humic acid, microbial biomass carbon and invertase activity in response to fertilization regimes in a long-term field experiment

A long-term located field for nutrients equipoise experiment in Fengqiu National Agro-ecological Experiment Station was conducted to investigate the effects of different fertilization on soil humic acid concentrations, soil microbial biomass, and invertase activities of fluvo-aquic soils. There are seven treatments of the experiment: organic manure (OM), half organic manure plus half fertilizer (1/2OMN), fertilizer NPK, fertilizer NP, fertilizer NK, fertilizer PK, and the control (CK, without fertilization). The results show that soil organic carbon and total nitrogen concentrations are significantly different with a similar pattern among fertilization regimes, and the order from high to low is OM, 1/2OMN, NPK, NP, PK, NK, which was just contrary to soil pH. Generally speaking, only organic manure increased soil humic acid significantly. In addition, OM had highest soil microbial biomass C and invertase activitiy, while 1/2OMN took the second place. It indicated that, long-term organic fertilization would be better on elevating soil fertility and health properties.