Effects of gibberellic acid spray on nitrogen yield efficiency of mustard grown with different nitrogen levels

Mustard is cultivated throughout the world for oil in its seeds. It requires high nitrogen input for improved productivity but the nitrogen applied to the soil is not fully utilised by the crops due to various constraints. The objective of the reported research was to determine if foliar- applied gibberellic acid (GA₃) could enhance crop growth and increase nitrogen-use efficiency. A field experiment was conducted during 1997-98 in which GA₃ (10^-5 M) was applied to foliage at 40d after sowing (pre-flowering) to mustard grown with 0, 40 (sub-optimal), 80 (optimal) and 120 (supra-optimal) kg N ha^-1. Foliar spray of GA₃ was effective only when plants received sufficient N (80 kg N ha^-1). GA₃ sprays significantly enhanced plant dry mass, leaf area, carbon dioxide exchange rate, plant growth rate, crop growth rate and relative growth rate. GA₃ -treated plants showed enhanced nitrogen-use efficiency through redistribution of N to seeds.