Biomass, Radiation Use Efficiency, and Nitrogen Utilization of Ratoon Rice Respond to Nitrogen Management in Central China

Ratoon rice is proposed as a promising way to improve rice productivity via increasing harvest frequency. Nitrogen (N) is the most effective in promoting the development and growth of ratoon plants. However, limited information is available on how different N management practices affect the biomass production of the ratoon crop (RC) through influencing canopy light interception, radiation use efficiency (RUE), and N utilization. Field experiments were conducted in central China in 2016 and 2017 to examine the effects of N management practices on the biomass accumulation of RC and the underlying physiological mechanisms. The N rates (100 vs. 200 kg N ha−1) in the main crop (MC) had a small and inconsistent effect on the biomass accumulation of RC. N application at 15 days after heading of MC for promoting bud development (Nbud, 100 kg N ha–1) increased total biomass production of RC by 17.2–19.1%, due to the improvements in both pre- and post-heading biomass production during the ratoon season (BPratoon). N application at 1–2 days after harvesting of MC for promoting the growth of regenerated tillers (Ntiller, 100 kg N ha–1) increased total biomass production of RC by 7.8–15.9% due to the improvements in post-heading BPratoon alone or both pre- and post-heading BPratoon. The differences in BPratoon caused by Nbud and Ntiller were associated with crop growth rate, leaf area index, RUE, and N uptake of RC. Total N uptake of RC was improved by Nbud through increasing stubble N content at harvest of MC and by Ntiller through increasing plant N uptake during the ratoon season. N use efficiency for BPratoon was reduced by Ntiller but not by Nbud. These results suggest that both Nbud and Ntiller play important roles in improving biomass production in RC, although Nbud was more efficient than Ntiller.