Trade-offs and synergies of conservation agriculture: Soil properties and crop performance after five years of minimum tillage and residue retention

Conservation agriculture (CA) practices have shown promise in various cropping systems globally, yet their effects on soil properties and yields in paddy-dominated intensive systems remain understudied. A five-year field experiment was conducted in the High Ganges River Floodplain (AEZ-11) of Rajshahi Division, western Bangladesh (approximately 24.4°N, 88.6°E) to evaluate crop establishment and residue management effects on soil properties and crop yields in a wheat–mungbean–rice rotation. The experiment followed a split-plot design with four replications. Main plots comprised two establishment methods: conventional tillage for upland crops and conventional wet tillage with puddling for rice (CT) versus minimum tillage using strip planting for upland crops with non-puddled rice transplanting (MT). Subplots compared residue retention (R+; 30 cm stubble height for wheat and rice plus full mungbean stover retention) against complete residue removal (R−). Wheat grain yields were significantly higher under MT with R+ (3.91–4.45 t ha⁻¹) compared to CT with R− across all five years, with yield advantages increasing over time. These yield gains coincide with improved soil moisture availability during critical growth stages and enhanced nutrient supply. Rice yields showed no significant difference between establishment methods (p > 0.05). After five years, MT with R+ significantly improved soil biological, physical and chemical properties compared to CT with R−: soil organic carbon increased from 0.67% to 0.92%, total nitrogen from 0.042% to 0.09%, and exchangeable potassium increased approximately threefold. Microbial populations were highest under MT with R+, including fungal spores (99 ± 8.8 per 100 g soil), Rhizobium (3.2 × 104 CFU g-1), phosphate-solubilising bacteria (3.8 × 105 CFU g-1), and Azotobacter (5.0 × 105 CFU g-1). These findings suggest that combining minimum tillage with residue retention progressively improves soil fertility, which may explain the increasing yield advantages observed in later cropping years.