Response of first flood irrigation timing after rice dry-direct-seeding: Productivity and greenhouse gas emissions in Central China

A major challenge in rice (Oryza sativa L.) production is to simultaneously achieve the goals of reducing water consumption, labor requirements and greenhouse gas (GHG) emissions while maintaining a sustainable grain yield. Dry direct-seeded rice (DDSR) has been proposed as an alternative rice production strategy because it reduces water consumption and labor requirements and increases system productivity. To evaluate the responses of grain yield, yield components, water productivity and GHG emissions to different first flood irrigation times under DDSR, field experiments were conducted under three different first-irrigation times: 15, 30 or 45 days after sowing (DAS) in 2014 and 15, 35 or 55 DAS in 2015. The precipitation in the 45 DAS was 291 mm in 2014 and 160 mm in 2015. The results indicated that the grain yields under DDSR were not affected by the different flooding times in 2014 but were significantly reduced when the first flood irrigation time was prolonged to 55 DAS in 2015. Delaying the first flood irrigation time after sowing conserved water and significantly increased water productivity (WP) under DDSR. Prolonging the first flood irrigation time after sowing markedly decreased the CH4 gas emission, although delaying the first flood irrigation time increased the N2O gas emission, the global warming potential was significantly reduced. Based on these findings, we put forward the recommendation that the timing of first flood irrigation can be postponed to 45 DAS with precipitation levels higher than 160 mm under DDSR in central China. However, long-term studies across different environments are inevitable to get definite conclusions.