Impact of variable tillage based residue management and legume based cropping for seven years on enzymes activity, soil quality index and crop productivity in rice ecology

Conventional tillage (CT) with excessive soil disturbance and crop residue removal in rice (Oryza sativa L.) - wheat (Triticum aestivum L.) sequence has been witnessed as an unsustainable practice in rice based cropping system. Climate resilient agro-techniques consisting with principles of risk mitigation and adaptation for sustainable agriculture such as zero tillage (ZT) is being adopted in south Asian countries. However, long-term impact of sequential ZT + residues addition in crop rotation after puddled rice (CT- ZT + R) on soil enzymes activity and soil quality index (SQI) are not adequately addressed. Experiment was conducted in split-plot design having four crop establishment techniques: (i) CT in each crop of rotation without residue (CT-CT), (ii) CT in each crop with incorporated residue (CT-CT + R), (iii) CT rice - ZT in post-rainy season crops without residue (CT-ZT), (iv) CT rice - ZT in post-rainy season crops with surface residue mulch (CT-ZT + R) each with three levels of crop rotations: (i) rice-wheat (R-W), (ii) rice-chickpea (Cicer arietinum L.) (R-C) and (iii) rice-chick-pea-mungbean (Vigna radiata L.) (R-C-Mb). CT-ZT + R enhanced 25% soil organic carbon (SOC) and 45% microbial biomass carbon (SMBC) over CT-CT (P < 0.05). Further, CT-ZT + R increased SMBC/SOC ratio by 31.4 and 16.7% (P < 0.05) over CT-CT, respectively. For SOC, SMBC and SMBC/SOC ratio, an order of R-C-Mb > R-C > R-W (P < 0.05) was observed. CT-ZT + R increased (P < 0.05) fluorescein diacetate activity by 17-31%, alkaline phosphatase by 4-25% and acid phosphatase by 16-31% over CT-CT + R and CT-CT. ZT in post-rainy season (CT-ZT + R) resulted in 21-37% higher beta-glucosidase and 25-31% protease activity than those of continuous CT. The interaction revealed that CT-ZT + R under R-C-Mb and R-C rotations increased (P < 0.05) 26% and 10% rice grain yield compared with CT-CT x R-W system, respectively. The SMBC had higher share (86-90%) towards SQI values followed by fluorescein diacetate (10-14%) and emerged as soil quality indicators in long-run. CT-ZT + R and CT-ZT increased 40% SQI values compared with CT-CT. Besides, R-C-Mb and R-C rotations had 13-35% higher SQI over R-W (P < 0.05). Thus, elimination of intensive tillage at least in post-rainy seasons after puddled rice with crop residues retention and cropping intensification with grain legumes can bring about higher rice productivity and soil quality in rice based ecologies.