Effects of nitrogen fertilization for bud initiation and tiller growth on yield and quality of rice ratoon crop in central China

Rice ratooning is an ancient technology, known as harvesting twice after one sowing. In recent years, ratoon rice has drawn much attention and been widely practiced by farmers in central China because of its advantages in saving labor and increasing profit. For ratoon crop (RC), nitrogen (N) application for promoting bud initiation (Nbᵤd) and for promoting regenerated tiller growth (Nₜᵢₗₗₑᵣ) are two common N management practices. However, it is still obscure about their effects on grain yield and quality of RC. Field experiments were conducted to compare the effects of Nbᵤd (75 kg N ha⁻¹ application at 12 days after heading of main crop, MC) and Nₜᵢₗₗₑᵣ (75 kg N ha⁻¹ application at 2 days after harvesting of MC) on the grain yield and quality of RC in 2018 and 2019. Compared to Nbᵤd, Nₜᵢₗₗₑᵣ had an evident and positive effect on grain yield, head rice percentage (HRP) and chalkiness degree (CD) of RC. Averaged across years, Nbᵤd and Nₜᵢₗₗₑᵣ increased grain yield of RC by 5.5 % and 30.5 %, respectively. Moreover, Nₜᵢₗₗₑᵣ improved grain quality with an increase of 10.5 % in HRP and a decrease of 10.2 % in CD. Nₜᵢₗₗₑᵣ significantly increased sink size like spikelets m⁻², and source ability including leaf area index, leaf N content, and crop growth rate in ratoon crop. The positive effect of Nbᵤd on grain yield of RC was positively correlated with the increase in panicles m⁻², but negatively correlated with the panicles m⁻² of MC. Nbᵤd has no effect on stubble dry weight, and significantly increased stubble N concentration, but significantly decreased stubble non-structural carbohydrate concentration at maturity in the main season. Overall, our results indicated that nutrient status of straw and panicle number in MC affected the roles of Nbᵤd on RC yield, and more attention should be paid on Nₜᵢₗₗₑᵣ in future RC production.