A field study was conducted at two locations (Jordan valley and Al-Jubeiha) with different rainfall levels, altitudes and temperature ranges. The study was established to evaluate the optimum planting density, nitrogen (N) form and irrigation level to attain the best quality of lettuce crop in terms of minimum nitrate (NO 3 ) content and to minimise the impact on the environment. Seeds of 'Amar' lettuce were sown 1 month before transplanting. Three forms of N fertiliser (Ca(NO 3 ) 2 , (NH 4 ) 2 SO 4 and CO(NH 2 ) 2 ) were applied at three times at a total rate of 100 kg N ha −1 . Three in-row spacings (15, 20 and 25 cm) were assigned. Two irrigation levels were applied: level 1 had twice the amount of irrigation water as level 2, which was achieved by doubling the number of irrigation lines. The results indicated that N form significantly increased both N and NO 3 contents. Ca(NO 3 ) 2 was the most effective in increasing the N and NO 3 contents in lettuce leaf tissues, followed by CO(NH 2 ) 2 and then (NH 4 ) 2 SO 4 . The outer leaves (green colour) had about five times the NO 3 content of the inner leaves (pale yellow colour). However, the effect of N form on production, total N absorption and N recovery was significant in the following order: (NH 4 ) 2 SO 4 > Ca(NO 3 ) 2 > CO(NH 2 ) 2 . Increasing the plant spacing resulted in a significant increase in N and NO 3 contents in the lettuce leaves.

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