Assessment of soil quality under different tillage practices during wheat cultivation: soil enzymes and microbial biomass

Microbial processes, particularly enzyme activities, play crucial functional roles in soil ecology, hence serving as sensitive indicators of soil quality. We assessed the temporal dynamics of microbial biomass and selected soil enzymes (beta-d-glucosidase, cellobiohydrolase, polyphenol oxidase, urease, glycine-aminopeptidase and alkaline phosphatase) during wheat cultivation, under four different tillage practices in the rice-wheat system. The four practices involved conventional tilling of soil before cultivating each crop (CTR-CTW); no tilling before cultivating rice but conventional tillage before wheat (NTR-CTW); conventional tilling before cultivating rice but no tilling before wheat (CTR-NTW) and no tilling before cultivation of each crop (NTR-NTW). Microbial biomass and activities of hydrolytic enzymes increased under NTR-NTW followed by CTR-NTW and NTR-CTW with respect to the conventional practice CTR-CTW, thus reflecting improvement in microbial activities with reduced tillage frequency. Enzyme activities generally depended on soil moisture and temperature, but nature of relationships varied among different practices. Nutrient demand appeared to be the strongest driver of alkaline phosphatase and urease, and soil temperature for glycine-aminopeptidase. Under CTR-CTW, activities of most of the extracellular enzymes were related with beta-d-glucosidase or urease, but such relations altered under rest of the practices. The study showed that extracellular soil enzymes respond sensitively to tillage practices as well as environmental variables, particularly soil temperature and moisture and hence can serve as a sensitive indicator of changes in soil processes. Considering improvement in microbial biomass and enzymatic activities as indicators of better soil quality, adoption of no tillage apparently improved soil quality. Still, more number of field studies are required under tillage managements to explore the relationships between different enzyme activities and environmental factors.