Zero Tillage with Residue Retention Enhances Macroaggregate Formation and Aggregate Stability in a Rice-Based Conservation Agriculture System under Differential Weed Management Options

Conservation agriculture, characterized by minimal soil disturbance, residue retention, and crop diversification, plays a vital role in improving soil health and sustainability in intensive cropping systems. However, limited information exists on the combined effects of conservation tillage and weed management on soil aggregation in rice-based systems. A field experiment was conducted during kharif 2014-2019 under the All India Coordinated Research Project (AICRP) on Weed Management, Rajendranagar, Hyderabad, to study the effect of conservation tillage and weed management options on soil aggregation in a rice–maize–Sesbania conservation agriculture system. The experiment was laid out in split-plot design with three replications. Five tillage treatments were assigned to main plots and three weed management treatments, viz., chemical weed management, integrated weed management (IWM), and unweeded control, to subplots. Soil aggregate size distribution, water-stable aggregate fractions, geometric mean diameter (GMD) and mean weight diameter (MWD) were determined before sowing and after harvest of the rice crop. Zero tillage with residue retention (T5: ZT+R–ZT+R) recorded the highest proportion of large macroaggregates (>4.75 mm: 34.7%; 4.75–2.00 mm: 19.2%), maximum water-stable large macroaggregates (WsLMac: 53.9%), and superior GMD (1.113 mm) and MWD (2.244 mm). Conventional tillage treatments recorded dominance of smaller, less stable aggregate fractions, indicating structural deterioration due to intensive tillage and puddling. Weed management practices did not significantly influence any aggregate parameter, and the tillage × weed management interaction was non-significant. The results conclusively indicate that adoption of zero tillage with crop residue retention significantly improves soil macroaggregate stability in rice-based conservation agriculture systems of the semi-arid tropics.