RESPONSE OF YIELD AND HEAD QUALITY OF LETTUCE TO NITROGEN FERTILIZATION AND SEAWEED EXTRACT FOLIAR APPLICATION UNDER NEW VALLEY CONDITIONS

Two field experiments were conducted at the Agricultural Research Farm of the Faculty of Agriculture, New Valley University, New Valley Governorate, Egypt, during the two successful seasons of 2022/2023 and 2023/2024 to study the effect of nitrogen fertilization at rates of 45, 60, 75, and 90 kg N/feddan in the form of urea and foliar spraying with seaweed extract (SWE) at concentrations of 2, 4, and 6 ml/l beside untreated control and their interactions between them on growth, productivity, nitrogen use efficiency (NUE), and head quality of lettuce cv. Dark Green, grown in sandy soil. The results clearly demonstrated that the interaction between fertilizing lettuce plants with 90 kg N/fed. and foliar spraying with SWE at 6 ml/l significantly enhanced plant growth parameters, leaf pigments, i.e., chlorophyll a, b, and carotenoides, head traits such as head diameter, head fresh weight, dry matter percentage in leaves, and the total yield (ton/fed.), leaves content of N, P, and K, total soluble solids, and vitamin C in both seasons. Moreover, this interaction treatment scored relative increases about 65.84% acreage of the two seasons over the interaction between fertilizing plants with 45 kg N/fed. and foliar spraying with distilled water (control plants). As for NUE and nitrate concentration in lettuce plants, fertilizing plants with 45 kg N/fed. and foliar spraying with SWE at 6 ml/l record the maximum NUE (average two seasons, 286.35 kg yield/one kg N) and the minimum nitrate concentration in leaves (average two seasons, 174.00 ppm). Despite the use of a high rate of nitrogen fertilization (90 kg/fed.) and spraying lettuce plants with SWE at 6 ml/l, which recorded the maximum yield per feddan, the percentage of nitrate (295.15 average two seasons) that was estimated in the leaves did not reach the maximum permissible limit of nitrates (2 g/kg DW).