Submergence tolerance in relation to application time of nitrogen and phosphorus in rice (Oryza sativa L.)

Transient complete submergence reduces survival and yield of more than 22 million ha of rice in rainfed lowlands and flood prone areas in Asia. Progress has been made in developing more tolerant germplasm, but fewer efforts have been devoted to identifying suitable nutrient management options. This study compared IR-64 Sub1 and IR-64 for their tolerance to submergence at active tillering, panicle initiation and heading stages. The effects of N and P application and their application time on the plant's tolerance to submergence were also examined. We measured shoot elongation, plant survival, specific leaf area, chlorophyll and non-structural carbohydrates (NSC) concentration. Both the cultivars suffered more to submergence at heading stage than other stages with devastating effects on IR-64. Post-submergence N and basal P application increased the concentration of NSC, enhanced survival percentage and reduced shoot elongation. Pre-submergence N application enhanced under-water shoot elongation, which leads to reduced survival, depletion of chlorophyll and NSC. Soluble carbohydrates after submergence are more important for survival than at the initial level, IR-64 Sub 1 could survived better under submergence because it possessed 12.5% more NSC after submergence as compared to IR-64. Plant survival and productivity in areas where untimely flooding is anticipated could be enhanced by post-submergence N and basal P application.