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Studies were conducted to determine the effects of irrigation on the yield and nitrogen recovery of field grown lettuce in the Bekaa Valley of Lebanon under non-limiting soil N conditions. Within the experimental plots, irrigation differentiation was made upon crop evapotranspiration (ETc) measured on a non-weighing lysimeter of 16 m2. The treatments included a control, I-100, irrigated at 100% of ETc, and two water deficit treatments, I-80 and I-60, irrigated at 80 and 60% of ETc, respectively. Prior to planting, all plots received fertilizers broadcast at a rate of 250 kg/ha of NPK-fertilizer (17%). At 6- and 12-leaf stages, ammonium nitrate (34.5%) was applied with irrigation water in two applications of 125 kg/ha each. Local groundwater containing 10 mg N-NO3/litre was used for irrigation. Yield was determined in a final destructive harvest. Crop evapotranspiration reached on the lysimeter a total of 433 mm for a total growing period of 70 days. Water stress caused by the deficit irrigations significantly
Karam et al. (Sun,) studied this question.