Analysis of Water Use in Rice Production under Paddy System and SRI in Ahero Irrigation Scheme, Kenya

Food security in Kenya is a challenge due to increasing demand from the growing population and impacts of climate change among other factors. The impact of climate change is felt on rainfall pattern in terms of seasonal variability and long-term change. Therefore, it is necessary to go beyond the normal intensification of food production to sustainable water management as well as the expansion of irrigated agriculture. The study was formulated to assess the performance of existing conventional paddy irrigation system compared to SRI technology in terms of efficient water use and rice yield and to develop alternative irrigation schedules for better rice production grown under limited water supply in surface irrigation. Randomized complete block experimental design with three replications was adopted to collect field data. The results were used as inputs to the CROPWAT irrigation management model. The model was used to estimate crop water requirements and net irrigation requirement. Results of the study indicated that Irrigation Water Use (IWU) in the SRI treatments was 2316.7 m3/ha compared to 2966.7 m3/ha in the conventional practice translating to a saving of 21.9%. On water productivity, SRI system demonstrated significantly higher water productivity (0.5 kg/m3) compared to conventional system with 0.3 kg/m3. SRI increased Water Productivity (WP) by 67% while Land Productivity (LP) increased by 59.5%. The FAO-CROPWAT model estimated water requirement for rice as 934.9 mm. The model was also used to determine irrigation schedule in that for SRI rice, the first irrigation was given 19 days before sowing date with 92.2 mm of net irrigation. After these, subsequent irrigations were given after -4, -2, 22, 29,22, 29, 36, 43, 50, 57, 64, 71, 78, 85, 92 and 94 days after sowing date with 90mm, 50mm, and 20mm for the rest of applications except the last application which was given 200mm. The gross irrigation for paddy is 931.7 mm considering an efficiency of 70% during each irrigation supplied. Simulations of irrigation at 100 % critical depletion and refilling the soil to field capacity (100%) resulted to 0% yield reduction and less irrigation water requirement (622.7 mm) though with a greater number of irrigation applications (60). However, irrigating with user defined intervals with respective user defined application depths resulted in a total of 827.2 mm, yield reduction of 2.8% and a reduced rain efficiency of 98.1%. Basing on the findings of this study, SRI technology is capable of producing considerable higher rice yields and much saving on irrigation water use as compared to conventional flooding system. When the irrigation scheduling using CROPWAT is adapted for SRI technology, one is able to adopt better water management system which saves irrigation water.

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