Effect of Different Levels of Irrigation and Fertilizer on Water and Nitrogen Productivity in Lettuce

Lettuce is one of the most important leafy vegetables used primarily for fresh and salad applications. The purpose of this study was to investigate the effect of different levels of water and nitrogen on lettuce yield and find the best irrigation and nitrogen fertilizer practices for producing this crop in drip irrigation. Iceberg variety of lettuce was planted in 2018 with three irrigation treatments (I1, I2 and I3 to provide 100%, 80%, and 60% of crop evapotranspiration, ETa, respectively) and four nitrogen treatments (N1, N2, N3, and N4 to provide 105, 70, 35 and zero kg of nitrogen per hectare in total, respectively). In 2019, two irrigation treatments (I1 and I3) and two nitrogen treatments (N1 and N4) were used. The experiment had a randomized complete block design with three replications. The results indicated that the effect of irrigation and nitrogen treatments and their interactions on the marketable yield of lettuce; but the dry matter produced was only affected by irrigation and nitrogen treatments. Maximum marketable yield and dry matter production were 66.1 ton.ha-1 and 2728.2 kg.ha-1 for full irrigation treatment with 105 kg.ha-1 nitrogen (I1N1) treatment, respectively. The minimum marketable yield and dry matter were 37.5 ton.ha-1 and 1929.6 kg.ha-1 for 60% ETa treatment with 35 kg.ha-1 nitrogen (I3N3) treatment, respectively. The maximum and minimum irrigation water productivities for marketable yield were 21.63 and 15.38 kg.m-3 for I2N1 and I3N3 treatments, respectively. The linear and nonlinear production functions of yield-water and yield-nitrogen were obtained for lettuce variety Iceberg, which can be used in similar environmental conditions in research and practical applications.