Evapotranspiration, water use efficiency and yield of rainfed and irrigated tomato

Field experiments were conducted to examine the variability in the pattern of water use (ET), water use efficiency and fruit yield of field grown rainfed and irrigated tomato during the late (post-rainy) sowing season in a humid zone of Nigeria. The annual pattern of rainfall and rainfed potential production of crops showed that the dry (post) rainy season is characterized by water adequacy index (Ao), which was calculated from rainfall and ETo ranging from 0.01-0.33 (Dec-March), The late sowing season falls within August-December (Ao less than 0.34) ending in a terminal drought situation while the wet/rainy season falls season falls between March/April to July with an Ao ranging from 0.34 to 1.0. The mean seasonal values of SE, Tr, ETa were 37.6, 38.5, 73.8 and 25.1, 25.8, 53.2 mm for the respective rainfed and irrigated tomato. Mean seasonal soil water evaporation (SE) ranges from 37 and 11 mm. per day which constituted 5.6 and 14.4% of ETa for the respective rainfed and irrigated fields. Trends in the values of soil water evaporation for both rainfed and irrigated fields showed that greater SE was obtained under rainfed tomato, which also had lower crop transpiration. Evapotranspiration efficiencies (ETE 0.35, 0.18 & 0.20, 0.12 kg water per kg dry matter) and crop water use efficiencies (WUE; 0.012, 0.20 & 0.013, 0.09 kg water per kg dry matter) for biomass and fruit yields in the respective rainfed and irrigated tomato. Transpiration efficiencies (TRE) measured for biomass and fruit were 1.94 and 2.22; 1.91 and 2.17 kg water per kg dry matter. Relative water use (ETa/Eo) and drought index values for the respective rainfed and irrigated tomato were 1.08, 0.11 and 0.49, 0.11. Over rainfed tomato, plant biomass (root & shoot dry weights) and leaf area were enhanced by irrigation and the improved growth was accompanied by high fruit yield and WUE.