Yield and nitrogen recovery of lettuce under different irrigation regimes.

Abstract

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