Changes of vegetable yields, soil chemical properties and microbial biomass to mid-term additions of organic and mineral fertilizer in South China

A comprehensive understanding of impacts of fertilization on soil biochemical characteristics and crop yield is essential to manage fertilization strategies in the vegetable production process. Here, we studied the soil in a green vegetable-eggplant system of South China located in Jiangsu province after five-year (from 2008 to 2012) repeated organic and mineral fertilizer amendments. The fertilization treatments were as follows: no fertilizer as control (CK), conventional mineral fertilizer (NPK), chicken manure (OM), mineral fertilizer combined with manure (OPT) and OPT plus phosphorus fertilizer (OPT+P). Vegetable yields were measured each year, and soil was sampled at the end of the experiment to analyze soil chemical and microbial biomass characteristics. Results showed that chicken manure application produced similar economic vegetable yields to mineral NPK fertilizer and OPT treatment resulted in the highest vegetable yields (126.9 t ha-1) among all the treatments (45-118.8 t ha-1). OM treatment led to increases in pH, soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) contents, while NPK treatment led to the reduction of pH and the promotion of ammonium-N and nitrate-N contents in soil. What's more, NPK, OM, OPT and OPT+P significantly increased SOC contents by 8.7, 25.2, 9.4 and 18.1% as compared with CK; especially addition of manure significantly increased the content of SOC fractions such as microbial biomass C and dissolved organic C. Interestingly, compared with OPT, OPT+P treatment significantly increased concentrations of soil nitrate-N and microbial biomass N by 7.4 and 176.7%, respectively. This implied that the addition of P fertilizer, to some extent, stimulated microbial activity leading to immobilization of N. Clearly, the application of mineral fertilizer combined with manure is a win-win strategy and recommended for promoting SOC sequestration and vegetable yields in the green vegetable-eggplant cropping system of South China.