Journal of Applied Horticulture. 2002: 4(2): 70-76

Yield and nitrogen recovery of lettuce under different irrigation regimes

Karam, F; Mounzer, O; Sarkis, F; Lahoud, R

Lebanese Agricultural Research Institute, Department of Irrigation and Agro-Meteorology, Tal Amara, P.O. Box 287 Zahle, Lebanon.

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 reduced leaf number, leaf area index and dry matter accumulation (p<0.05). Water deficit also reduced final fresh weight by 20 to 30% with comparison to the control. Nitrogen recovery reached 218 kg N/ha at maturity compared to control, while consistent reductions averaging 35 and 40% were observed under I-80 and I-60, respectively. Nitrogen use efficiency (NUE) also decreased markedly in the less irrigated treatments.