INFLUENCE OF NITROGEN ON INDIAN MUSTARD GROWN UNDER DIFFERENT LEVELS OF STORED SOIL-MOISTURE

Responses of Indian mustard to different levels of stored soil moisture (100, 90, 75 and 60% of field capacity) and nitrogen doses (0, 30 and 60 kg ha-1) were studied. Decreasing moisture levels caused a general decline in all observed parameters. Nitrogen fertilization enhanced the soil moisture extraction (especially below 40 cm depth) and increased the water use through larger leaf area, particularly during the vegetative period without affecting the water use during the reproductive phase. An increase in nitrogen dose increased dry matter production, seed yield, water use efficiency, nitrogen and phosphorus uptake coupled with increased levels of total chlorophyll, starch, reducing sugars, soluble protein and free amino acids, despite a consistent decline in plant water potential and percentage relative turgidity at all levels of stored moisture. Notwithstanding the decline in the activities of nitrate reductase and glutamine synthetase under low soil moisture, the increase in glutamate dehydrogenase activity on one hand and nitrogen mediated increases in all these enzymes irrespective of soil mositure status, on the other, possibly helped the fertilized plants to maintain ammonia assimilation.