الفهرس 
Effect of nitrogen fertilization and growth seasons on yield and quality of lettuce
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Abstract
In modern agriculture, the nitrate accumulation in vegetables has
become a serious threat to human health. That caused by an imbalance
between nitrate absorption and assimilation in plants. Nitrogen fertilization
and light intensity are the main factors affected nitrate accumulation.
Therefore, a pot experiment was conducted during two successive summer
and winter seasons of 2019 at the greenhouse of Fac. Agric., Cairo Univ.,
Giza, Egypt, on lettuce (Lactuca sativa L. var. longifolia Lam) plants to
investigate the effect of growth seasons (summer and winter), different rates
(0, 60, 90 and 120 Kg N fed-1
) and sources CO (NH2)2, NH4NO3 and
(NH4)2SO4 of nitrogen fertilizers on lettuce growth and nitrate
concentrations. The results showed that fresh and dry weight, yield and
nutrient contents of lettuce plants gradually increased according to
increasing dose of nitrogen, up to 90 Kg N fed-1
and the magnitude of
increase, according to different N fertilizers used , was in the following
order: CO (NH2)2 > NH4NO3 > (NH4)2SO4. The accumulation of nitrate was
higher in winter compared to summer season for both inner and outer
leaves. The highest values for both seasons were recorded in the outer
leaves, which significantly increased with increasing N fertilizer dose and
the magnitude of increase, according to N sources used, was in the
following order: NH4NO3 > CO(NH2)2 > (NH4)2SO4. This study
recommend the combined use of urea rate at 90 Kg N fed-1
in summer
season to achieve the highest yield with acceptable nitrate content