Evaluation or water use at Sagana irrigation scheme in Nyeri District
The study objective was to improve water use efficiency at Sagana gravity fed sprinkler irrigation scheme. An optimal cropping system for Sagana Irrigation Scheme was developed using; climatic data, crops data, farmers preferences, and market prices. An irrigation schedule to promote water use efficiency was developed for crops in the optimal cropping system using the FAD package CRDPWAT. French beans, which is the main cash crop at Sagana Irrigation Scheme was subjected to different water application depths and Nitrogen fertilizer rates to: i) determine the yield response factor; and ii) study water and fertilizer interactions. A line source sprinkler irrigation system was used to apply different amounts of water with irrigation scheduling according to the soil water balance. The water application depths were; 21.1 mm, 180.3 mill, 158.2 mm, and 138 mm. Four Nitrogen fertilizer rates (0 kg/ha, 80 kg/ha, 120 kg/ha, and 160 kg/ha) were randomized within the experimental plots. The major findings of the study were: i) Water use efficiency at Sagan a Irrigation Scheme can be improved by designing an optimal cropping system that exploits the existing climatic conditions. .i i.) The developed optimal cropping system had a peak water requirement of 114 mrn during the month of January. iii) For efficient water use under the optimal cropping system, rotational irrigation as opposed to ondemand irrigation is recommended. iv) A yield response factor of 1.1 for French beans was determined. v ) Increased use of Nitrogen fertilizer at the same water level had a positive effect on the yields of French beans.