Effect of Continuous Monocropping of Tomato on Soil Microorganism and Microbial Biomass Carbon

Soil microorganisms play an important role in recycling and transformation of nutrients. Soil microbiological parameters and microbial biomass carbon (MBC) have been suggested as possible indicators of soil quality. Soil microorganisms and MBC in different continuous cropping soils were investigated. Results showed that bacterial population was the highest, followed by actinomycetes, and fungi were the lowest at 0–30 cm soil depth. The amount of soil microorganisms decreased with increasing soil depth (0–10 > 10–20 > 20–30 cm). Soil microbial ratios at different depths proved to be responsive to time (year) variations in continuous monocropping tomato, except those at 0–10 to 10–20 cm depth for fungi and 10–20 to 20–30 cm depth for bacteria. Soil MBC for 12 years of continuous cropping was significantly lower than those for 5, 8, and 10 years (P < 0.05). Continuous cropping years, soil depth, and the interaction of these two parameters significantly influenced soil fungal, bacterial, and actinomycetes populations and MBC. Bacterial population at the 0–10 cm soil layer was a sensitive indicator of continuous cropping of tomato. Soil fungal count increased with increasing monocropping time within 5–8 years.