Crop rotation and residue management effects on soil enzyme activities, glomalin and aggregate stability under zero tillage in the Indo-Gangetic Plains

This 3-year study investigated the effects of crop rotation and residue management (surface retention of residues under zero tillage) on soil carbon pools, selected soil physical properties (soil aggregation, mean weight diameter) and biological properties (glomalin and ergosterol contents, soil respiration and enzyme activities) and their inter-relationships in a semi-arid soil of India under rainfed condition. The field study consisted of three different cropping systems (pearl millet-wheat, pearl millet-chickpea and pearl millet-mustard) in the main plots and three residue management practices (no residue, crop residue and Leucaena mulch cover) in the sub-plots, with three replications. All crops were cultivated adopting zero tillage (ZT). Surface (0-15 cm) samples were taken from fields after 3-years. Results revealed that crop rotation had no impacts on total soil organic C (SOC), Walkley-Black C (WBC) and soil aggregation, but significantly affected labile C. However, residue retention or addition significantly affected total SOC, labile C and soil aggregation. Plots under crop residue and Leucaena mulching had similar to 30 and 26% higher large macroaggregates (> 2 mm diameter) than no residue treated plots. A similar trend was observed for the proportion of macroaggregates, resulting in about 20 and 17% increase in mean weight diameter (MWD), respectively, in the crop residue and Leucaena added plots compared to the residue removal plots (similar to 0.91 mm). The residue retained plots had similar to 40 and 13% higher soil glomalin content compared with residue removal (similar to 290 mu g g(-1) soil) and Leucaena added plots, respectively. Both soil glomalin and ergosterol contents were significantly (P < 0.05) related with large macroaggregates and there were significant relationships between glomalin and WBC concentration and glomalin and MWD in the surface soil. Glomalin, microbial biomass C, dehydrogenase, fluorescein diacetate (FDA), glucosidase and alkaline phosphatase activities were significantly increased by both crop rotation and residue management. Thus, the legume based cropping system (pearl millet-chickpea system) with ZT and residue retention under rainfed conditions had significant impact on soil aggregation and biological health, even after a short-term adoption.