Agronomic responses of ratoon rice to nitrogen management in central China

Rice ratooning is becoming an important component of rice cropping system in central China because of its low production costs. However, low and unstable grain yield in ratoon season has limited the wide adoption of this technology. Nitrogen (N) management is the most critical in improving the grain yield of rice crops. The objective of this study was to compare the effects of different N treatment on the grain yield and yield attributes of ratoon crop (RC). Two widely planted varieties, Liangyou6326 (LY6326) and Huanghuazhan (HHZ), were grown for rice ratooning in field experiments in Qichun County, Hubei Province, central China in 2016 and 2017. The grain yield of RC ranged from 2.96 to 6.49 t ha(-1) across N treatments, varieties, and years with total growth duration of 61 to 84 d in the ratoon season. Application of 100 kg N ha(-1) at 15 d after heading of the main crop (MC) for promoting bud development (N-bud ) increased the grain yield of RC by 12.7-55.4%. The yield improvement by N-bud was attributed to increased panicles m(-2 )in the ratoon season. Application of 100 kg N ha(-1) at 1-2 d after cutting of MC for promoting the development of regenerated tillers (N-tiller) increased the grain yield of RC by 11.5-35.5% only when N-bud was not applied, and the yield improvement was due to increased panicles m(-2) or spikelets panicle(-1) or both in the ratoon season. The N rates in MC (100 vs. 200 kg N ha(-1)) had relatively small and inconsistent effects on the grain yield of RC. Our results indicated that both N(bud )and N-tiller were critical for improving the grain yield of RC, although N-bud was more effective than N-tiller under the conditions of our study.