OPTIMUM SEED RATE AND NITROGEN-FERTILIZER REQUIREMENT OF RICE UNDER SEMI-DEEP-WATER ECOSYSTEM

The effect of varying seed rates (100-1000 seeds m(-2)) and nitrogen f ertilizer (0-60 kg N ha(-1)) applied either in a single basal dose or in splits was investigated on a tall elongating, photosensitive rice v ariety, Nalini, under semi-deepwater conditions (0-100 cm) during 1993 and 1994 at Cuttack, India. Seedling emergence was higher in 1993 (53 .9 %) than in 1994 (44.1 %) and it increased proportionately with incr easing seed rate. Increase in the number of tillers and panicles m(-2) at higher seed rates was associated with a corresponding decrease in panicle weight. Regression analysis indicated a decrease of 0.91-1.28 g in panicle weight for an increase of 100 panicles m(-2). The grain y ield of rice was significantly higher at 400 seeds m(-2) in 1993 and a t 600 seeds m(-2) in 1994 than at low seed rates but further increase in seed rate did not increase the yield. Application of N fertilizer i ncreased the panicle number and thereby grain yield significantly. The effect of basal and split applied N at active or maximum tillering st ages as well as between 30 and 60 kg N ha(-1) was not significant on t he grain yield. The results suggest that a basal dose of 30 kg N ha(-1 ) and seeding density of 400-600 seeds m(-2), resulting in 40-50 % see dling emergence and 150-200 panicles m-2, each with 2.0-2.5g weight, m ay be adequate for optimum productivity of rice under semideepwater co nditions.