| China’s suitable area for ratoon rice cultivation is estimated at approximately 5.6 million hectares,predominantly located in sub-suitable regions.The forage-grain ratoon rice introduces a dual-season cropping strategy,focusing on forage harvest in the main season and rice production in the subsequent ratoon season.This approach addresses the issues of poor grain quality in the main season and the low yield of ratoon rice by optimizing temperature and light resource allocation and enhancing forage for livestock husbandry.The mowing method and nitrogen fertilizer rates are important cultivation measures affecting the yield and quality of ratoon rice.While prior studies have examined these practices’impacts on ratoon rice growth,their effects on the yield and quality of the main crop forage and the sustained impact on population quality and ratoon yield require further exploration.Thus,a split-split plot experimental design was conducted at the Henan Agricultural University Experimental Station in Guangshan County,Xinyang City,Henan Province,during 2021 and 2022.The main plots were assigned to varieties（Taoyouxiangzhan and Liangyou 6326）.Nitrogen fertilizer rates(135,270,and 405 kg ha-1)were applied in the split plots,while the split-split plots included mowing periods（heading,milk-ripening,dry-ripening,and full maturity stages）and mowing heights（0,15,25,35,and 45 cm）.Various indicators such as ratoon yield and quality,population quality,temperature and light utilization,forage yield and quality,and the dry weight and non-structural carbohydrate concentration of stubble were measured to explore the regulatory effects of different cultivation measures on the yield and quality of forage-grain ratoon rice.Furthermore,the study compared the systemic productivity,energy efficiency,net profits,and carbon-nitrogen footprints between forage-grain ratoon rice and conventional ratoon rice in both suitable and sub-suitable areas,clarifying the environmental and economic benefits of the forage-grain ratoon rice system.The main results are as follows:（1）Mowing during the heading and milk-ripening stage significantly enhanced the ratoon yield,primarily attributed to increased panicle numbers and grain per panicle,with a significant increase in panicle number.This mowing method elevated temperature and light exposure,thereby improving the population quality.Heading-stage mowing resulted in a60.73%and 72.82%increase in the dry weight of ratoon rice at heading and maturity,respectively,while milk-ripening-stage mowing led to a 22.87%and 45.36%increase.Furthermore,optimizing mowing timing with increased nitrogen fertilization significantly enhanced stubble dry weight and non-structural carbohydrate content,thus improving ratoon capacity.Regression analysis revealed a significant positive correlation between stubble dry weight,non-structural carbohydrate content,and ratoon ability.Moreover,mowing during the heading to milk-ripening stages was shown to improve the processing and appearance quality of ratoon rice.At the mechanistic level,path analysis indicated that environmental factors directly impacted ratoon rice yield or indirectly influenced it through population quality.The growth of stubble primarily relied on ratoon ability to indirectly affect ratoon yield.Additionally,redundancy analysis and hierarchical partitioning analysis clarified the crucial roles of accumulated temperature,daily mean temperature,and ratoon ability in regulating ratoon yield,as well as the significance of daily mean temperature and total radiation in determining ratoon rice quality.（2）The yield and the number of panicles in ratoon rice both increased with the elevation of mowing heights,with the average yield in 2022 exceeding that of 2021.No significant yield differences were noted among the 25 cm,35 cm,and 45 cm cutting heights,yet yields at these heights were substantially higher than those at 0 cm and 15 cm.Elevating the mowing height to between 25 cm and 45 cm enhanced the average daily temperature and light exposure,thereby fostering the growth of ratoon rice and ratoon ability.Additionally,an optimal mowing height proved key in enhancing rice quality,with the highest milling rates for both varieties achieved at a 35 cm cutting height and with a nitrogen application of 270 kg ha-1 in 2021.Appropriate nitrogen fertilizer rates were essential for enhancing the quality of the ratoon rice population.Compared with 105 kg N ha-1treatment,270 and 405 kg N ha-1 treatments significantly increased post-flowering dry matter accumulation and crop growth rates by24.23%-33.56%and 16.17%-23.87%,respectively.Furthermore,the rates of brown rice,milled rice,and whole rice under these higher nitrogen treatments exceeded those achieved with the 105 kg ha-1 application,although the 405 kg ha-1 rate adversely affected the rice’s appearance.Hierarchical analysis indicated that average daily radiation and the dry weight at the heading stage were crucial for yield determination,while temperature utilization rate and tiller number significantly influenced rice quality across different cutting heights and nitrogen levels.（3）Compared with 105 kg N ha-1,forage yield with 270 kg ha-1 and 405 kg ha-1 increased by 9.30%and 20.95%,respectively;Crude protein content and metabolizable energy increased by 1.54%-1.99%and 3.00%-4.80%.The 270 kg N ha-1 treatment can also decrease fiber content while increasing starch content,thereby improving the digestible dry matter and relative feeding value of forage harvested at heading and milk-ripening stages.Moreover,the crude protein content and metabolized energy in forage cut from heading to milk-ripening stage increased by 1.42%-2.93%and 12.31%-14.54%,respectively,compared with mowing at full-maturity stage.At 35-45 cm mowing height,neutral and acid detergent fiber decreased by 4.46%-8.37%and 5.84%-9.14%,respectively,compared with 0 cm height treatment,while crude protein and starch contents increased by 1.34%-1.83%and 1.05%-2.24%,respectively.（4）Economic income and energy outputs were significantly improved by mowing during heading and milk-ripening period,along with optimal nitrogen level treatments.However,mowing height treatment had no significant effect on economic income,although a higher mowing height was associated with reduced energy outputs.Compared with conventional ratoon rice cultivation,the energy output and utilization rate of forage-grain ratoon rice were increased by 36.84%and 36.67%,respectively,and the global warming potential and eutrophication potential were decreased by 17.07%and 12.81%,respectively,under the treatment of mowing at milk-ripening stage,25 cm height and 270 kg ha-1 nitrogen fertilizer.In the sub-suitable planting area,forage-grain ratoon rice had greater potential to increase yield.Compared with conventional ratoon rice,forage-grain ratoon rice ratoon yields surged by 151.73%in Chizhou and 91.34%in Xinyang,with net profit significantly rising in Chizhou.In conclusion,within sub-suitable areas for ratoon rice,integrating precise mowing timing,stubble height,and nitrogen fertilizer level significantly enhances ratoon rice growth,yield,and both rice and forage.This strategy also mitigates environmental impact by optimizing temperature and light resource distribution across growing seasons.Specifically,mowing from the heading to milk-ripening stage and the applicating of 270 N kg ha-1significantly improve ratoon rice and forage quality and yield.Mowing at the milk-ripening stage with 15-25 cm stubble height and applying 270 kg N ha-1 optimizes energy efficiency and economic gains,achieving sustainable and profitable ratoon rice production. |
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