Flooding is one of the major harmful abiotic stresses in the low lying areas of Asia and crop losses due to submergence are considerably high. Along with plant breeding techniques, agronomic management options in general and nutrient management in particular should be taken into consideration. Response of Sub 1 and non-Sub1 cultivars of rice to post-flood nitrogen (N) management under variable flood water was compared at maximum tillering stage. Submergence tolerance on survival, leaf senescence, metabolic changes, and anti-oxidant enzymatic activities were evaluated. Sub1 cultivars proved their superiority over IR-20 in terms of significantly higher survival, anti-oxidant enzymes and lower metabolic changes. Turbid water resulted in lower survival because of poor light transmission, chlorophyll retention and silt deposition. Basal phosphorus reduced the elongation, senescence and ethylene accumulation. Post-flood foliar spray of urea substantially increased the chlorophyll, soluble sugars and extenuated ethylene accumulation resulting in significantly higher survival. These nutrient management options can provide opportunities for better survival and productivity even under turbid water, helping farmers to cope with the existing problems in flood-prone areas.

The impact of submergence on the allometry, changes in metabolic activities and antioxidant enzymes during oxidative stress in four Indica rice varieties namely IR-20, IR-64 Sub1, Swarna Sub1 and Savitri Sub1 was studied. The differential response of flooding under clear and turbid water with different nutrient application schedules was also examined during and after 12 days of complete submergence. Submergence substantially reduced allometric parameters and the activities of antioxidant enzymes but increased the % change in chlorophyll, soluble sugars and malondialdehyde (MDA) across cultivars with drastic effects on IR-20. Turbid water resulted in higher leaf senescence, lodging, higher depletion of chlorophyll and soluble sugars because of poor light transmission. Pre-submergence N application resulted in higher lodging, leaf senescence and higher MDA level but depletion of chlorophyll and NSC leading to higher % change over prior to submergence. Basal P application reduced the senescence and lodging, whereas increased the antioxidant enzyme activities. Foliar spray of postsubmergence N with basal P improved the retention and regain of chlorophyll, soluble sugar and increased the dry matter, leaf area and root shoot ratio. Crop establishment could therefore be enhanced in areas where untimely flooding is anticipated by applying basal P and foliar spray of urea after desubmergence.

Flooding is the major abiotic stress in flood-prone rice ecosystems, where duration, severity and turbidity of flooding are the factors negatively affecting survival and crop growth worldwide. Advances in physiology, genetics, and molecular biology have greatly improved our understanding of plant responses to stresses, but nutrient-management options are still lacking. This study was conducted to investigate the combined effect of silica (Si), phosphorus (P) and nitrogen (N) with Sub1 and non-Sub1 cultivars of rice under clear and turbid water submergence. Submergence tolerance effects on allometry, metabolic changes, photosynthetic rate and ethylene accumulation were evaluated. Application of Si reduced elongation, lodging and leaf senescence, with more prominent effects when applied with basal P. Combined effect of Si, N and P significantly improved, growth, photosynthetic rate, concentrations of chlorophyll and soluble sugars of rice after flood recovery, which led to higher plant survival. The findings of the study suggest that combined application of Si, N and P can significantly contribute to higher survival of rice seedlings and establishment thereafter in flash-flood prone areas.