Response of soil moisture content, evapotranspiration, and yield of cowpea to varying water application

Moisture stress is an important factor affecting field-grown cowpea in the tropics, especially in the dry seasons, and irrigation is required for successful yields. Field experiment was conducted at Teaching and Research Farm of the Department of Agricultural Engineering, Federal University of Technology, Akure, during 2014 growing season using a completely confounded design with four replicates to evaluate the impact of soil moisture stress on the yields of cowpea under four different irrigation treatments. The treatments were 100%, 80%, 60% and 40% Full Irrigation Treatment (FIT). Soil moisture contents were determined biweekly using gravimetric method. Cowpea grain and biomass yields were measured after harvest. The yield response factor (Ky) was determined to evaluate the plant response to irrigation. The point where Ky and the ratio ratio of yield reduction and ET reduction are numerically equivalent was determined. The ET production function was implemented in MATLAB to accurately determine the optimum soil moisture and irrigation water required for cowpea production. The results of the study indicated that 100% FIT excelled all other treatments at grain yield and biomass yield, where its yield was 1.06t ha−1, the 80%, 60% and 40% FIT produced 0.95, 0.89 and 0.71 t ha−1 respectively. The analysis of the results showed that soil moisture availability were significantly (P<0.05) affected by the irrigation treatments adopted, which in turn significantly (P ≤ 0.05) affected the cowpea grain and biomass yield. The yield obtained at 40% FIT was significantly (P<0.05) different. The yield response factor of 1.24 was obtained, showing that cowpea is sensitive to water stress. The total amount of irrigation water and moisture content that resulted to the optimum yield were 151.12mm and 0.1082g/g, respectively. The result implies that 32% of total irrigation water applied during the growing season would be saved. The approach adopted, therefore, proved to be useful in estimation of possible irrigation water required for optimum production of cowpe