Vegetable yields and soil biochemical properties as influenced by fertilization in Southern China

Nitrogen (N) fertilizer is commonly excessive in vegetable production, which greatly increases the risk of N loss and may eventually lead to the contamination of adjacent surface and ground water bodies. We assessed the effects of different fertilizer treatments on vegetable yields and soil biochemical properties, with the aim to develop best fertilizer management strategy for vegetable production. A five-year study (from 2008 to 2012) was conducted on a vegetable field in Jiangsu Province, southern China, with six fertilizer treatments: no fertilizer (control; CK), mineral fertilizer (NPK), chicken manure (OM), manure combined with mineral N fertilizer (OPT), OPT plus additional N fertilizer (OPT + N) and OPT plus additional phosphorus (P) fertilizer (OPT + P). Vegetable yields were measured each year, multiple soil (0-20 cm) chemical and biochemical characteristics were analyzed at the end of the study. Moreover, the soil ammonia-oxidizing microbial community structure was analyzed based on the PCR-DGGE method. Results showed that all fertilizer treatments produced higher economic vegetable yields than CK, with the highest yields in OPT. Combined application of manure and mineral fertilizer (OPT, OPT + N and OPT + P) produced higher yields than OM and NPK that had similar yields. All treatments with manure promoted soil carbon, N and P levels and reduced the potential of soil acidity. The OPT + P treatment performed best in enhancing soil fertility, which, for example, increased the concentrations of soil total-N, nitrate-N and microbial biomass N by 15.8%, 51.0% and 53.5%, respectively, compared to OPT. In addition, the OPT + P treatment had the highest abundance and diversity of ammonia-oxidizing archaea (AOA), which was positively correlated to the soil ammonium-N and nitrate-N concentrations. Possibly, the additional P in OPT + P could stimulate soil microbial activity, with positive implications for N fertility. However, the OPT + P treatment may also increase the risk of N loss due to an increasing soil nitrate-N, making it a less desirable fertilizer management strategy. In conclusion, the combined application of organic and chemical fertilizers without additional N or P (OPT) is suggested to be the best fertilizer management strategy that can improve soil fertility and vegetable yields, and meanwhile reduces the potential of N loss from soil.