A Detailed Study on the Effects of Regulated Deficit Irrigation on the Growth and Yield of Lettuce (Lactuca sativa L.) Grown in the Malkerns Area, a Region in the Kingdom of Eswatini (Southern Africa)

Water is fast becoming an economically scarce resource in many areas of the world, including Eswatini, especially in arid and semi-arid regions. Deficit irrigation (DI) is a well-accepted practice to optimize and or increase water use, thereby saving cost, by allowing crops to withstand mild water stress with no or only marginal decreases in yield and quality traits. A study to test the response of lettuce (Lactuca sativa L.) to deficit irrigation was conducted in a field plot experiment at the Faculty of Agriculture at the Luyengo Campus of the University of Eswatini. The treatments were laid in a randomized block design. The experiment consisted of four treatments, each replicated three times. Treatment 1 (T1) was irrigated daily, treatment 2 (T2) irrigated after 2 days, treatment 3 (T3) irrigated after 3 days and treatment 4 (T4) irrigated after 4 days. A total of 30 lettuce plants were planted in each treatment. The lettuce was grown for a period of four weeks and then harvested whole. Yield parameters measured included the number of leaves, the plant height (cm), leaf area index (LAI) and the fresh and dry head mass (grams). Significant differences (P < 0.01) between treatments T3 and T4 were obtained for fresh and dry lettuce head mass. The highest water use efficiency and crop water productivity were obtained in treatment T3. It was concluded that irrigating lettuce every three days was the best option for the area under the conditions of the experiment. However, irrigating every after four or more days would result in significantly lower yields than expected, which could be a loss to the farmer.