nitrogen fertilizer

winter wheat

nitrogen fertilization

petiole sap

nitrate content

tomato plants

ammonium nitrate

shoot dry

corn

In order to determine the effect of nitrogen fertilizer rates and cultivars on growth and critical yield of lettuce, an experiment was conducted at Shahid Chamran University of Ahwaz, Iran during 2005-2006. This study was arranged in a spilt plot experiment based on a randomized complete block design, in three replications. The treatments included four nitrogen rates (0, 60, 120, and 180 kg N ha -1 ) as the main plot and two lettuce cultivars (‘Pich Ahwazi’ and ‘Pich Varamini’) as the sub-plot. Sampling was done in 86, 100, 114, 126, 142, and 156 days after sowing. The criteria measured were plant length, fresh and dry weights of leaves, leaf area, number of leaves, crop growth rate (CGR), leaf area index (LAI) and yield. Results indicated that different levels of nitrogen fertilizer on all growth characteristics were significant at P<0.01. Nitrogen fertilizer caused head formation to accelerate and delayed the bolting date of lettuce. Cultivar had a significant effect on growth characteristics, on fresh and dry weights of leaves and on leaf number but not on plant length and leaf area. The highest yield was obtained with 120 kg ha -1 treatment by ‘Pich Ahwazi’. Also, it took ‘Pich Varamini’ longer to form a head and to flower than ‘Pich Ahwazi’.

Effect of Different Levels of Nitrogen Fertilizer and Cultivars on Growth, Yield and Yield Components of Romaine Lettuce (Lactuca sativa L.)