Nitrate content in lettuce (Lactuca sativa L) heads in relation to plant spacing, nitrogen form and irrigation level

Abstract

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.

Effect of different day and night nutrient solution concentrations on growth, photosynthesis, and leaf NO3- content of aeroponically grown lettuce

“…These results are more significant in D25/N50 because the total amount of NO3-N applied as fertilizer is also reduced with a 25% reduction compared with a constant solution (D50/N50). Among the fertilization management strategies proposed to reduce NO3 -in lettuce leaves, varying the ratio of NO3 -to other nutrients in the solution (Gent, 2003) and replacing NO3 -by other N forms (Abu-Rayyan et al, 2004) have received most of the attention. However, these strategies do not reduce total N fertilizer applied to the system, which does not reduce N released to the environment.…”

“…-by other N sources such as urea or amino acids (Abu-Rayyan et al, 2004;Pavlou et al, 2007), and supplying NO3 -in accordance with irradiance levels (Demsar et al, 2004).…”

Production system and harvesting stage influence on nitrate content and quality of butterhead lettuce

“…The nitrate accumulation varies in various part of plant and physiological age of the plant. In most types of lettuce, including butterhead type, the highest concentration of nitrates is normally observed in the external leaves (Abu Rayyan et al, 2004). The NRA also varies with plant structures especially the leaf.…”

Effect of nitrogen levels and sources on production of Swiss Chard (Beta vulgarisvar.Cicla)

“…The nitrate content of lettuce was found to be the highest where calcium nitrate was used as a nitrogen source followed by urea and then ammonium sulphate (Abu-Rayyan et al, 2004). The nitrate content of cauliflower curds was also significantly lower where urea was applied as nitrogen source compared to ammonium sulphate, ammonium nitrate and calcium nitrate (Kaniszewski & Rumpel, 1998).…”