Long-term effects of pig slurry application on selected soil quality parameters and tissue composition of maize in a subhumid subtropical environment

Effects of long-term application of pig slurry (PS) on soil organic carbon (SOC) pools, nutrients and maize tissue composition under continuous conventional tillage in a maize-soyabean rotation system in subhumid subtropical environments are unclear. The soil and plant parameters have important implications for PS management under intensive agriculture. Soil (0-20 cm depth) and maize tissue were sampled from lands treated with PS for 0, 10 and 20 years and analysed for soil chemical properties and plant nutrients. Soil available phosphorus, potassium, copper and zinc and tissue concentrations increased due to PS application. Total nitrogen and SOC declined, whereas soil microbial biomass carbon (MBC), hot-water-soluble carbon (HWSC) and microbial quotient (MB/SOC) increased with PS application period. The SOC was negatively correlated to MBC and HWSC (r = -0.472 and -0.663, respectively). Increase in MBC, MBC/SOC and HWSC indicated presence of an untenable soil organic matter with limited possibility of carbon sequestration. The findings imply that long-term PS application, with conventional tillage, not only increased most plant nutrients but also vulnerability of SOC.