Organic fertilizer application increases biomass and proportion of fungi in the soil microbial community in a minimum tillage Chinese cabbage field

This study evaluated the variations in soil microbial communities in a minimum tillage upland field used for Chinese cabbage (Brassica rapa L.) cultivation by their fatty acid methyl ester (FAME) and chemical properties. Replicated plots received organic fertilizer (OF), chemical fertilizer (CF), and no fertilizer (NF), and microbial communities were analyzed in the early season, mid-season and harvesting stages. The electrical conductivity of the CF soil at mid-season was significantly higher than that of the OF and NF soils (P <0.05), whereas the NO3-N content at the harvesting stage was significantly lower in the CF soil than in the OF soil (P <0.05). The average microbial biomasses in the OF soils during the Chinese cabbage growing period were approximately 1.03 similar to 1.27 times higher for fungi, Gramnegative bacteria, total bacteria, total FAMEs, Gram-positive bacteria, and arbuscular mycorrhizal fungi (AMF). Organic fertilizer had a significantly lower ratio of cy19:0 to 18:16)7c then CF (P <0.001), which indicates that a decrease in microbial stress was caused by organic matter soil inputs and the lack of chemical amendments. Communities of fungi in OF soils were significantly larger than those in CF soils (P <0.001) indicating fungi are potentially responsible for the microbial community differentiation between the OF and CF treatments in an upland field. However, the average microbial communities in the OF soils were approximately 0.86 times lower for actinomycetes and 0.95 times lower for AMF. In communities of total bacteria (P <0.001), Gram-negative (P <0.001) and Gram-positive bacteria (P <0.01), the interaction between the growth stage and the fertilizer showed significant differentiation. Further work is needed to relate the seasonal variation and impact of fertilization on microbial communities to productivity of Chinese cabbage in Korea.