The effect of irrigation management on crop water requirement and crop water productivity of tomato and sweet corn in Kibwezi, Kenya
Research on crop water requirement and productivity is important to reduce agricultural water use in arid and semiarid areas (ASAL), where water is a limited resource. A study was conducted to determine crop water requirement and evaluate crop water productivity of tomato (Lycopersicon esculentum L. var. M82) and sweet com (Zea mays L. var. Renat) under drip and sprinkler irrigation systems, respectively, in Kibwezi. The study objectives were (i) to determine crop water requirement (ETcrop), (ii) to evaluate yield response to different irrigation water application rates and (iii) to evaluate the effect of different irrigation water application rates on crop water productivity (CWP). Treatments involved reducing the sprinkler irrigation hours for sweet com and increasing the drip irrigation interval for tomato. The experimental design was a randomized complete block design (RCBD) with six main treatments, replicated thrice for each crop under the respective irrigation system. Crop water requirement (ETcrop) values were computed using pan evaporation method. Sweet com requires most water during the development stage, these· stage accounted for 52 and 54 % of the total seasonal ETcropfor the first and second crop, respectively. For tomato, ETcrop was found to be critical during the development and the mid stage, this being 298 and 269 mm/season which accounts for 73 and 76 % of the total growing seasonal ETcropfor the first and second crop, respectively. The highest sweet com yields of 11.84 and 10.88 t ha-1 were obtained from the treatment irrigated for 2.5 and 3 hours, which corresponds to 769 and 882 mm of total irrigation (TI) (irrigation plus effective rainfall) for the first and second crop, respectively. The highest tomato yields of 24.74 and "9.20 t ha-1 were obtained from treatment with irrigation interval of 4 days which corresponds to 819 and 732 mm of TI for the first and second crop, respectively. Both the yields of sweet com and tomato were correlated with TI, at P :s 0.05. The results imply that, 2.5 hours or an average 791 mm of sprinkler irrigation water applied at an interval of three days is adequate for sweet com production under the prevailing climatic condition, thus saving an average of 41 mm or 5 % of the irrigation water from the 3 hours or an average of 832 mm of TI that is currently applied. On the other hand, 3 hours of drip irrigation can be applied after an interval of 4 days for tomato production without XIV significantly affecting the yields. This corresponds to an average of 776 nun of TI, thus saving an average of 233 nun or 23 % of the irrigation water from the 3 days interval or 1009 mm of TI water that is currently applied. Crop water productivity (CWP) for sweet com ranged from 1.44 to 2.71 kg m" for the first crop and from 1.01 to 1.97 kg rn" for the second crop, while for tomato, it ranged from 2.06 to 4.31 kg m-3 and from 0.76 to 1.65 kg m-3 for the first and second crop, respectively. Sweet com highest CWP value obtained for the first and second crop was 2.71 kg m-3 and 1.97 kg m" for the treatment irrigated for 2.5 hrs, with average seasonal actual crop evapotranspiration (ET) of 436 and 532 mm, respectively. For tomato the highest CWP value was obtained for treatment with irrigation interval of 4 days, which corresponds to 4.31 kg m-3 with ET of 574 mm and 1.65 kg m-3 with ET of 558 mm for the first and second crop, respectively. Both the CWP for sweet com and tomato were correlated with ET, at P S 0.05. It can be concluded that under the current irrigation practice the two crops are over irrigated. The saved water can be used to increase the hectarage under production, or enable the intensification of the crops already in production. Crop water productivity study is critical in determining the adaptation and productivity of plants in water-limited areas under the present climate.