Impact of zero-till residue management and crop diversification with legumes on soil aggregation and carbon sequestration

Abstract

We evaluated the long-term impact of zero tillage (ZT) in post–rainy seasons (winter and summer) crop/s, crop residue management, and crop diversification on soil aggregation and carbon sequestration. The field experiment (started in 2009) was undertaken in split-plot design for seven consecutive years on a sandy loam soil of Kanpur, India. The experiment comprised of four tillage and crop residue management treatments: PTR – conventional tillage (CT) without crop residue (PTR–CT), PTR – ZT without crop residue (PTR–ZT–R), PTR – CT with crop residue incorporation (PTR–CT+R), and PTR – ZT with surface crop residue retention (PTR–ZT + R) in main plot, and three cropping systems: rice–wheat (RW), rice–chickpea (RC), and rice–chickpea–mungbean (RCMb) in subplot. Treatment PTR–ZT + R resulted in 13% (p < 0.05) higher water stable macroaggregate over the PTR–CT. Meantime, PTR–ZT+R increased carbon content in macro- aggregate (28%) and meso-aggregate (39%) over the PTR–CT, because of added carbon through the surface-laden crop residue. The tillage and crop residue management followed the sequence of PTR–ZT+R > PTR–ZT–R > PTR–CT+R > PTR–CT (p < 0.05) across the soil depths for active and passive carbon pools. After seven years, PTR–ZT+R enhanced soil microbial biomass carbon (SMBC) and particulate organic carbon (POC) by 70 and 56% over PTR–CT, respectively. The RCMb and RC rotations increased (p < 0.05) the macro– and meso– aggregates, and aggregate mean weight diameter compared to the RW rotation in both soil depths. Crop rotations had the following trend: RCMb > RC > RW (p < 0.05) for SMBC and POC. Notably, treatment PTR–ZT+R with RCMb or RC rotations largely increased the carbon management index compared to the PTR–CT and RW systems. The structural indices and soil carbon parameters were significantly correlated to the rice grain yield, except microaggregated carbon. Thus, crop diversification with grain legume/s, zero tillage in post rainy season crop/s, and crop residue retention provided not only higher soil aggregation but also increased carbon sequestration in Inceptisol of subtropical humid climate.