Microbial properties of rhizosphere soils as affected by rotation, grafting, and soil sterilization in intensive vegetable production systems

The increased use of rotation, grafting, and soil sterilization has been documented to increase crop yield in intensive vegetable production systems in China. It is believed that these practices can promote changes in the rhizosphere that enhance early growth of plants. A 2-year greenhouse experiment on tomato double-cropping systems was conducted to investigate the effects of different agricultural treatments on microbial properties of rhizosphere soils and tomato fruit yield. The treatments included planting of welsh onion as a cover crop in the summer fallow (SF) period (CW), rotating vegetable chrysanthemum and tomato (CT), planting graft-tomato instead of auto-root tomato (GT), sterilizing soil with calcium cyanamide in the SF period (TC), and fallowing in the SF period (Control). Microbial population was analyzed by dilution plating. In general, microbial populations were higher in CT, GT and TC than in control. Fungal population was higher in TC whereas a high number of bacteria were found in CT. Soil microbial biomass C and N, total microbial population, organic C and total N showed significant positive correlations (P ≤ 0.01) with each others, and tomato yield showed significant positive correlations (P ≤ 0.05) with organic C, total N and total microbial population. In most treatments, CW, GT and TC significantly (P ≤ 0.05) increased tomato yield by 8%, 21% and 19% in four growing seasons, respectively. CT significantly (P ≤ 0.05) increased tomato yield by 26% in the spring season of 2007. These results suggested that rotation, grafting and soil sterilization could lead to changes in the microbial properties of plant rhizosphere and consequently increase plant yield. Additionally, the responses of plant yield were complex dependent on rhizosphere soil microbes in rotation-, grafting-, and soil sterilization-induced systems.