Effects of Long-term Lowland Rice-Maize Rotation on Soil Structure under Varying Residue and Tillage Management in the Philippines

Rotating upland crops with puddled rice is an effective strategy to reduce resource use and increase farm productivity under increasing challenges like water shortage and pests. Conflicting soil structure requirements of paddy and upland crops, however, prevent the system from reaching its potential. Plowpans used for puddling rice restrict rooting depth and create anaerobic stress in upland crops like maize. Optimized tillage and residue management could mitigate this, although studies are limited, particularly under a long-term scenario. The 24-year long rice-maize experiment at the International Rice Research Institute (IRRI) offers one of the world’s most extensive opportunities to study long-term management effects and improve practices for one of the most important cropping systems in the world. Within this experiment we compared measurements of bulk density (0-80 cm), soil moisture, water stable aggregates, infiltrability, penetration resistance, electrical conductivity, soil temperature, soil water bypass flow (AWD tube readings), and root depth/density under zero-tillage and conventional tillage with residue removed and returned in rice-rice and rice-maize rotations. Rice-maize rotation, zero-tillage and residue returned significantly improved soil moisture status and anaerobic conditions, water stable aggregates, infiltration, soil temperature, and root depth/density. Bulk density and penetration resistance were strongly affected by the relationship of soil moisture and shrink/swell properties, which was shown to be an overlooked metric in rice soil science. The results of this study suggest that the conventional practice of tillage with residue removal is counterproductive for long-term improvement of soil structure in paddy-upland rotation. Advisor: Charles Franci