Mowing and nitrogen management guidelines for superior rice ratoon yields

Abstract

Forage-grain ratoon rice (FG-RR) is a dual-cropping system, with forage harvested in the initial season and grain during the regeneration phase. While it is known that the timing of mowing and nitrogen (N) fertilization are key drivers that influence FG-RR production, physiological mechanisms ensuing mowing and N fertilizer application remain unclear. We conducted field experiments in 2021 and 2022 to investigate the yield and growth characteristics of ratooned crops (RC) under various mowing treatments (heading, milk-ripening, dry-ripening and maturity) using three N levels (135, 270, and 405 kg ha−1), two rice genotypes, Taoyouxiangzhan (TYXZ) and Liangyou 6326 (LY6326). Our results demonstrate a significant increase in ratoon yield when mowing occurred at heading or milk-ripening stages compared with maturity, with a yield increase of 2.2-fold when mowing occurred at heading. Early mowing stages increased stubble biomass (up to 73 %) and non-structural carbohydrate (up to 198 %) compared with that at maturity. Mowing at heading or milk-ripening improved accumulated temperature and light exposure, and when coupled with higher N application (270 kg ha−1 N), amplified ratoon ability to recover. Collectively, these factors raised leaf area index, canopy light interception and biomass. Hierarchical partitioning analysis underscored the substantial yet indirect influence of environmental drivers of ratoon yield, alongside a direct driver of growth, particularly thermal sum. We conclude that mowing at heading and milk-ripening with 270 kg ha−1 N elicits optimal ratoon yield with forage production, although further studies are required to determine how these guidelines vary across environments.