Growth, radiation use efficiency and yield of new cultivars of wheat under variable nitrogen rates

The experiment was conducted on four cultivars i.e. C1 (MH-97), C2 (Iqbal- 2000), C1 (Aqaab-2000) and C4 (V-95153) and three N fertilizer levels i.e. N1 (60 kg ha-1), N2 (l20 kg ha-1) and N3 (180 kg ha-1). The cultivar treatments were randomized in main plots and N levels in sub-plots respectively. The plot size was 2.0 x 5.0 m2 and there were 8 rows (25 cm apart) in each plot. Cultivars differed significantly in case of yield components with mean values i.e. plant height (87.23 cm), total tillers (459.39 m2), fertile tillers (415.42 m2), infertile tillers (44.81 m2), spike length (12.40 cm), number of spikelets per spike (18.04), number or grains per spike (56.25), 1000-grain weight (41.28 g), grain yield (5004 kg ha-1) and straw yield (8806 kg ha-1). Cultivar Aqaab-2000 gave higher harvest index (38.60%) followed by lqbal-2000 (35.83%), V-95153 (35.70%) and MH-97 (33.93%). Nitrogen fertilizer 120 kg ha-1 gave the highest grain yield of (5759 kg ha-1) followed by 180 kg ha-1 (4838 kg ha- 1) and 60 kg N ha-1 (4414 kg ha-1). Grain yield was significantly affected by cultivars the average the maximum grain yield was obtained in cv. Aqaab- 2000 with 120 kg N ha-1. Cultivar and N application significantly influenced TDM at final harvest. Generally cv. C3 (Aqaab-2000) and 120 kg N ha-1 enhanced TDM over other cultivars (cv. Iqbal-2000, V-95153 and MH-97). Differences in TDM among different cultivars and N levels were significantly different throughout the season. Mean seasonal TDM ranged from about 153.25 gm2 on 5 December to 1381,10 g m2 on the final harvest. The mean seasonal LAI declined from 14 February (6.47) to 15 March (2.14). All treatments showed significant effect on LAD and it ranged from 482.84 to 402.56 days. The cultivar Aqaab-2000 with 120 kg N ha-1 significantly enhanced LAD over V-95153, lqbal-2000 and MH-97. All the treatments showed significant effect on mean CGR varied from 8.91 gm2 day-1 on Aqaab-2000, 8.31 gm2 day-1 on V-95153, 8.24 gm2 day-1 on lqbal-2000 and 7.77 gm2 day-1 on MH-97. The seasonal mean CGR was 8.35 gm2 day- 1. All the treatments had significant effect on mean NAR, which ranged from 3.15 gm2 day-1 on MH-97, 3.14 gm2 day-1 on Iqbal-2000, 3.05 gm2 day-1 on Aqaab- 2000 and 2.95 gm2 day-1 on V-95153. All the treatments showed significant effect on grain growth. The cultivars showed the significant effect on the light interception which ranged from 640.15 MJ m2 in Aqaab-2000, 626.41 MJ m2 in V-95153, 612.46 MJ m2 in Iqbal-2000 and 584.33 MJ m2 in MH-97 while 120 kg N ha-1 had significant effect on the crop for light interception. The cultivars showed the significant effect on light use efficiency for TDM and grain yield. While N (120 kg ha-1) had also significant effect on the light use efficiency for TDM and grain yield. Mean value of light use efficiency for TDM was 2.24 g MJ-1, while 0.81 g MJ-1 for grain yield. The general conclusion for this study is that the grain yield among various treatments was related to their photosynthetic activity. The improvement to grain yield through changes in LAI may perhaps contribute in this regard. LAI decreased from 14 February harvest onward throughout the whole period of growth. The data suggested that there is considerable scope to exploit the yield potential of wheat with different management practices, depending upon the prevailing climatic conditions. It may be concluded from this study that cultivar Aqaab-2000 is the best one as compared to other cultivars and nitrogen rate (120 kg ha-1) is the optimum rate for achieving higher yield.