Nitrogen assimilation potential, periodic nitrate reductase activity and its relationship to grain protein in field grown rice in presence of butachlor

Effect of butachlor on nitrate reductase activity, nitrogen and protein content in the leaves at different stages of growth and protein content in grains was examined in rice variety RP-2421. The butachlor was applied at three concentrations, viz. 1.5 kg ha⁻¹, 2.0 kg ha⁻¹ and 2.5 kg ha⁻¹ four days after transplanting (4 DAT) alongwith hand weeding (30 DAT and 60 DAT) and weedy check. At all the stages of development, hand weeding twice (30 DAT and 60 DAT) and butachlor 1.5 kg ha⁻¹ being statistically at par maintained their superiority in increasing nitrate reductase activity, nitrogen content and protein content in rice leaves over all other treatments. Irrespective of the treatments nitrate reductase activity, nitrogen content and protein content in rice leaves increased up to 30 days and declined thereafter to minimal level up to 90 days. A positive correlation was observed in nitrate reductase activity and grain protein and in leaf protein and grain protein.