Nitrogen Management on Improving Resilience of Flood-Tolerant (Sub1) Rice Varieties in Flood-Prone Rainfed Lowlands

Flash flood causing submergence adversely affects rice production in vast areas of rainfed lowlands of South and Southeast Asia. Introgression at the Sub1 locus by molecularly assisted backcrossing incorporated tolerance into varieties traditional/modern high-yielding varieties and has released some varieties for commercial planting by Indian farmers. In the present study, we investigated the application of fractional N to further improve the survival and productivity potential of two Sub1 introgression varieties, Sambha Mahsuri-Sub1, and BR11-Sub1.Thirty days (d) old seedlings were transplanted, and 28-d after transplanting i.e. 58 days old seedlings were completely submerged for 18-d. Full doses of phosphorus and potassium were applied as a basal, while nitrogen was applied in split doses. Plant survival was recorded at 0, 5 and 20 days after de-submergence (AS) to study the recovery dynamics of cultivar Sub1. Results evidently established that varieties with higher biomass, tiller number, total chlorophyll and soluble sugars concentrations before flooding have higher survival rates after water drainage. They also had faster growth and better recovery, which was reflected in yield characteristics and grain yield. The 20-day and 40- day AS N application replenished flood-disturbed soil N pools, resulting in higher N uptake and N-use efficiency. These results may contribute to better nitrogen fertilization programs for rice crops and improve stress tolerance in newly developed tolerant rice varieties. It is evident from perusal of results that treatment T2 i.e.1/4 N applied as a basal and rest of residual N applied in three split doses respectively after de-submergence on days 5, 20 and 40 resulted in higher survival thanT1 and T3 respectively minimising mortality rate. This method of nitrogen fertilization (T2) also significantly affected plant-1 stem biomass, plant-1 tiller number, total chlorophyll, and soluble sugar concentrations before and after flooding. Based on these findings we proposed that application of lower dose of N (30kg/ha) as basal and rest amount of N in three split doses along with P and K (40kg/ha) in the field might be exploited to improve submergence tolerance and to obtain higher yield under flood prone ecosystem due to higher survival after de submergence corresponding to less post oxidative damage through proper N management during before and post submergence period.