Effect of nitrogen form, plant spacing and water regime on lettuce plants (Lactuca sativa L.)

A field study was conducted in Jordan Valley and Al-Jubeiha, Jordan, during 2000/2001 to study the optimum planting density, form of nitrogen and irrigation regime for lettuce cv. Amar. Seeds were sown one month before transplanting. A total of 100 kg pure N/ha was applied in the form of Ca(NO3)2, (NH4)2SO4, and CO(NH2)2. The N fertilizer was applied at 3 different times during plant development (25 kg N/ha applied at 3 weeks after transplanting, 25 kg N/ha applied at 5 weeks after transplanting, and 50 kg N/ha applied at 7 weeks after transplanting), and in-row spacing of 15, 20 and 25 cm were used. Two irrigation regimes were evaluated in the trials, i.e. regime 1 (~40 litre m-2 week-1, which was higher by two-fold than the amount of irrigation supplied under regime 2) and regime 2. At harvesting, the vertical and horizontal diameters of the head, number of leaves, leaf area, fresh and dry weights of head, and total fresh yield were determined. The effect of N form on production and vegetative parameters of lettuce head (vertical and horizontal diameter, number of leaves, leaf area, and fresh and dry weights) followed the order (NH4)2SO4 > Ca(NO3)2 > CO(NH2)2. Plant spacing also had a highly significant (p