The underlying mechanism of variety-water-nitrogen-stubble damage interaction on yield formation of ratoon rice with low stubble height under mechanized harvesting

Agronomic measures are the key to promoting the sustainable development of ratoon rice by reducing the mechanically crushing damage to the residual stubbles of the main crop, thereby mitigate the impact on axillary bud sprout and yield formation of ratoon rice. This study used widely recommended conventional rice Jiafuzhan and hybrid rice Yongyou 2640 as materials to conduct a four factor block design field experiment in a greenhouse of Fujian Agricultural and Forestry University Experimental Farm from 2018 to 2019, including fertilizer and no fertilization, alternate wetting and drying irrigation and continuous water flooding irrigation, and artificially crushing damage on rice stubbles and non-artificially crushing damage on rice stubbles experiments. At the same time, a 13C stable isotope in-situ detection technology was used to fertilize the pot experiment. The results displayed that there was significant interaction among varieties, water management, nitrogen application and stubble status. Relative to the long-term water flooding treatment, sequential application of nitrogen fertilizer coupled with moderate field drought for root-vigor and tiller promoting before and after harvesting the main crop, significantly improved the effective tillers from low position nodes. This in turn increased the effective panicles per plant and grains per panicle through reducing the influence of artificially crushing damage on rice stubbles and achieving high yield of the regenerated rice. Furthermore, the partitioning of 13C assimilates to the left stubble and its axillary bud was significantly improved at the mature stage of the main crop, while the translocation rate to roots and rhizosphere soil was reduced at the later growth stage of ratooning season rice, which was triggered by the metabolism of hormones and polyamines at the stem base regulated by the interaction of water and fertilizer in this time. We therefore infer that to achieve high yield of ratoon rice with stubble height under mechanized harvesting, timely application of nitrogen fertilizer is fundamental, coupled with moderate field drying for root-vigor preservation and tiller promotion before and after mechanically harvesting of the main crop.