Effects of consecutive turnover of green manure and N fertilizer on soil microbial biomass and enzyme activity in tobacco-planted field.

The objective of this study is to investigate the effects of consecutive turnover of green manure (ryegrass (Lolium perenne L.)) on soil microbial biomass C and N and enzyme activities. The results showed that the incorporation of green manure in tobacco-planted fields generally significantly enhanced enzyme activities (soil para nitrophenol (PNP), urease, catalase, and sucrase) and soil microbial biomass contents. The extent of enhancement increased with the increase in consecutive turnover. The C and N contents in microbial biomass were significantly lower in conventionally cultivated soil than in soils from the green manure-incorporated field. This finding indicated that incorporation of green manure could stimulate the activity of soil microorganisms. The average improvement gained from the T3 treatment (three-year consecutive cultivation of green manure since the harvest of tobacco) relative to the T0 treatment (conventional cultivation without any green manure) over the whole growth period of tobacco was 1.34 to 1.52 times for urease activity, 1.11 to 1.19 times for PNP activity, 1.58 to 1.17 times for sucrase activity, and 1.24 to 1.50 times for catalase activity. Overall, the activities of soil enzymes correlated well with the soil microbial biomass C and N. This study provides guidance on the measurement of green manure to manage the activation of soil microbial biomass and improve the quality of tobacco-planted soil.