Sustainable forage-grain ratoon rice production: interactions between planting density and mowing time on forage and grain attributes

Forage-grain ratoon rice (FG-RR) is a sustainable system designed to enhance ratoon rice yield and quality while simultaneously producing high-quality whole-plant rice forage through early harvesting of the immature main crop (MC) for silage. This study examined the effects of planting density and mowing time on forage and grain productivity and quality, to optimize ecological and economic benefits. Field experiments were conducted using two cultivars, Liangyou 6326 and Taoyouxiangzhan, across five planting densities (17.26 × 104–34.52 × 104 hills ha−1) and four mowing stages (heading, milk-ripening, dry-ripening, and full maturity). Forage and ratoon crop (RC) yields, quality traits, resource utilization efficiency, and economic returns were assessed. Increasing planting density initially promoted but subsequently reduced both forage and RC yields. Delayed mowing increased forage yield but, after an initial rise, reduced RC yield. The optimal combination-mowing at the milk-ripening stage with a planting density of 28.82 × 104 hills ha−1 produced forage containing 53.72% neutral detergent fiber, 21.26% starch, and 9.93% crude protein, meeting standards for high-quality silage. In the RC season, the head rice rate reached up to 58.61% with a chalkiness level as low as 4.17%, meeting high-quality edible rice standards. TOPSIS analysis and economic evaluation indicated that this management strategy yielded the highest overall performance, generating 3086.08 USD·ha−1. Integrating this optimal mowing time with optimal density produced 31.88 t·ha−1 of high-quality forage and 7.13 t·ha−1 of premium-grade rice. This integrated strategy enhances resource utilization efficiency, grain quality, and profitability, offering a practical approach for the sustainable development of FG-RR systems.