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Effect of split application of N at different physiological stages was studied. Total dose of 100 Kg. of N was supplied to the rice crop IR60 adopting four treatments bnesides the normal treatment i.e., 50:25:25. Sufficient N supplied from the panicle initiation onwards favoured for better source activity and sink capacity. Improvement in panicle Number, spikelet Number, filled spikelet due to the appropriate treatment favoured for the concomitent increase in the grain yield and harvest index.

The field experiment was conducted to observe the effect of combined heat and drought stress on Catalase, Peroxidase, Nitrate reductase and Soluble protein contents to screen and study the biochemical basis of heat and drought tolerance in three rice genotypes (ADT 43, TKM 9 and N22). The stresses were imposed at panicle initiation (PI) and anthesis stages of crop growth. The genotype N22 was found to be tolerant followed by TKM 9 while ADT 43 was observed to the susceptible genotype based on the above biochemical traits. Irrespective of genotypes, anthesis stage stress brought about accumulation of antioxidant enzymes and soluble protein compared to stress at PI stage. ADT 43 recorded low catalase activity of (6.91 µg H 2 O 2 min-1 g-1), peroxidase activity of (4.35 Δ 430 nm g-1 min-1), soluble protein content (11.05 mg g-1) and Nitrate reductase activity of (14.52 µg NO 2 g-1 h-1). While, N22 recorded higher catalase activity of (7.32 µg H 2 O 2 min-1 g-1), peroxidase activity of (5.68 Δ 430 nm g-1 min-1), soluble protein content (11.01 mg g-1) and Nitrate reductase activity of (15.84 µg NO 2 g-1 h-1). Higher antioxidant enzymes activity coupled with more soluble protein and Nitrate reductase activity was clearly demonstrated in the tolerant genotype (N22) compared to susceptible genotype (ADT 43). These results confirm that these biochemical traits may be used to screen rice genotypes for combined stresses and understand the mechanism underlying stress tolerance.