Nitrogen use efficiency of 15N-labelled urea applied to mustard (Brassica juncea L.) grown on a typic ustochrept

A field experiment was conducted to study the relative uptake of soil and fertilizer N by three mustard cultivars viz., Pusa Barani, Pusa Bold and Bio 902 at 0, 40, and 80 kg N/ha and to determine the losses of N from the applied urea by 15N recovery method. A 15N balance sheet was constructed based on crop recovery, nitrogen losses and soil retention. The results indicated that mustard cultivars responded to N application up to 80 kg/ha. Dry matter yield, N content, N uptake and per cent Ndff by mustard cultivars significantly increased with increase in the level of fertilizer N. Per cent Ndff significantly increased from 12 at 40 kg N/ha' to 22 at 80 kg N/ha' in mustard seed while in stover the corresponding values ranged from 11 to 20 . Successive levels of N also increased significantly the uptake of soil N by mustard cultivars clearly establishing the 'priming' or 'added nitrogen interaction effect' of applied nitrogen. The 15N uptake, recovery and utilization were significantly influenced by N level and cultivar. Nitrogen utilization by mustard ranged from 46 to 55 per cent, and increased with increased N level. The 15N balance sheet shows that the utilization at both the levels of applied N was higher in cv. Bio 902 (53 to 65 ) than in Pusa Barani and Pusa Bold which were found to be on par with each other. The agronomic and physiological use efficiencies (AUE and PUE) ranged from 14.0 to 14.6 kg seed/kg N added and 21.5 to 22.3 kg seed/kg N absorbed, respectively. The AUE was slightly higher at 40 kg N/ha while PUE was more at 80 kg N/ ha. The cv. Bio 902 recorded the highest AUE while Pusa Bold recorded the highest PUE. The residual 15N in soil ranged from 11 to 25 which decreased at higher level of applied N. The soil N recovery was maximum in cv. Pusa Bold followed by cv. Pus a Barani and minimum in cv. Bio 902. The 15N losses of applied urea ranged from 27 to 39 and were greater at higher N level and were more in cv. Pusa Bold.