Soil enzyme activity under organic versus conventional vegetable production systems

There has been a growing trend in using soil enzymes as indicators for changes in soil quality under different management practices. Although literature on this subject has tremendously grown in the last 10 years, most of the studies have focused on cultivated fields. However, research on cultivated vegetable soils also has significant implications. Experiments were conducted at two close-by fields (one under organic farming and the other under conventional farming) in Shanghai to investigate the influence of different horticultural farm management practices on soil enzyme activities. Four combinations of field type and management system — organic management in greenhouse (GO), conventional management in greenhouse (GC), organic management in open-field (LO) and conventional management in open-field (LC) conditions — were evaluated. Soil sampled at the 0~20 cm depth were analyzed using the traditional soil analysis method. Furthermore, proteinase, urease, dehydrogenase, β-glucosidase and nitrate reductase activities were determined. The results presented here fostered an in-depth understanding of the impacts of management practices on soil enzyme activities. Soil electrical conductivity (EC) under organic managements was less than that under conventional management by averages of 12% and 16% in greenhouse and open-field conditions, respectively. The levels of microbial biomass C and N under organic managements were higher than those under conventional managements. Significant differences were noted in proteinase and prease activities among the different management practices. Proteinase, urease, dehydrogenase and β-glucosidase activities were comparatively high under organic management, while nitrate reductase activity was low. Management practices significantly affected proteinase and urease activities with P values of 0.006 8 and 0.012 4 respectively. Environmental conditions of cultivation significantly influenced proteinase, urease, β-glucosidase and nitrate reductase activities. Enzyme activities were higher in organic managements under greenhouse conditions than in other treatments. Analysis showed that proteinase, urease, dehydrogenase and β-glucosidase activities were closely correlated (at significant levels) with total dissolved nitrogen, microbial biomass C and microbial biomass N. In summary, organic systems significantly improved soil microbial characteristics and increased soil organic C, which in turn enhanced soil enzyme activities. Moreover, proteinase, urease, dehydrogenase and β-glucosidase activities were suitable indicators for soil fertility. Further studies that focus on determining the relationship between soil microbial diversity and specific enzyme activities under different management systems using the DGGE (denaturing gradient gel electrophoresis) technique were therefore recommended.