Organic Farming Improves Soil Microbial Abundance and Diversity under Greenhouse Condition: A Case Study in Shanghai (Eastern China)

Agricultural practices have significant impacts on soil properties and microbial communities; however, little is known about their responses to open field and plastic tunnels under organic and conventional farming. We therefore investigated the responses of soil chemical variables and microbial communities to different agricultural management and cultivation types, including organic management in open field (OF), organic management in plastic tunnels (OP), conventional management in open field (CF) and conventional management in plastic tunnels (CP), by using a pyrosequencing approach of 16S rRNA gene amplicon. Both factors had significant influences on the soil properties and microbial communities. Organic farming increased the nutrient-related soil variables compared to conventional farming regardless of cultivation type, especially for the available N and P, which were increased by 137% and 711%, respectively, in OP compared to CP. Additionally, OP had the highest microbial abundance and diversity among treatments, whereas no difference was found between OF, CF and CP. Furthermore, OP possessed diverse differential bacteria which were mainly related to the organic material turnover (e.g., Roseiflexus, Planctomyces and Butyrivibrio) and plant growth promotion (e.g., Nostoc, Glycomyces and Bacillus). Redundancy analysis (RDA) showed that pH, electrical conductivity (EC), nutrient levels (e.g., available N and available P) and total Zn content were significantly correlated to the structure of the microbial community. Overall, our results showed that the long-term organic farming with high fertilizer input increased soil nutrient levels and microbial abundance and diversity under plastic-tunnel condition compared to other cultivation systems