EFFECTS OF DIFFERENT IRRIGATION LEVELS ON YIELD OF LETTUCE GROWN IN AN UNHEATED GREENHOUSE

This study was carried out in an unheated greenhouse in order to determine effects of different irrigation levels on lettuce yield (cv. Hazar) grown from December to February in Şanlıurfa, Turkey. Different irrigation water amounts based on Class-A-Pan evaporation were applied to the plants by drip irrigation system at four irrigation levels (Kp1= 1.0, Kp2=0.75, Kp3=0.50, Kp4=0.25) in one week irrigation interval. Applied irrigation water and evapotranspiration of Kp1 treatment were 118 and 125 mm, respectively. The highest average lettuce yield of 7.8 ton da-1 was obtained from the full-irrigation treatment (Kp1). Significant differences were not observed between Kp1 and Kp2 treatments in terms of lettuce yield. Maximum irrigation water use efficiency and total water use efficiency were obtained from Kp4 treatment respectively with 0.117 and 0.074 ton da-1 mm-1. Yield response factor (ky) was found to be 0.88. The research results showed that a 7 day irrigation interval with Kp2 treatment could be used for irrigating lettuce under the unheated greenhouse conditions without any significant yield loss but increased water use efficiencies