The National Irrigation Board in Kenya is promoting a rice production system (SRI) to improve food security. The programme combines using certified seeds and intensive water management with high levels of farmer sensitization.
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A Study of the African White Rice Stem Borer (Maliarpha separatella Rag.) Population Density Fluctuations at Mwea Irrigation Scheme in Central Kenya
The African white rice stem borer (Maliarpha separatella Ragonot) is a major pest of rice in Kenya. To understand and develop appropriate management packages, its population dynamics were studied at Mwea irrigation scheme in Central Kenya. This was for two wet and two dry periods. Farmer fields located in different parts of the scheme and outside the scheme were sampled every fortnight. Farms sampled represented five water provision schedules (System of Rice intensification (SRI), rain fed, flood irrigated, sporadic irrigation, and fallow period). Five planting regimes (on season, off season double cropping, ratoon, and late planting) and three management styles (controlled by National Irrigation Board (N.I.B), not controlled by N.I.B and out-growers) were studied. During each sampling, a 1mx1m quadrant was used randomly and pest counted on all the plants within the quadrant. Results showed that the number of M. separatella varied significantly (p<0.05) in the scheme. Pest densities were highest in off season planted rice (13.1). High numbers were also found in Non N.I.B controlled fields with sporadic irrigation (8.1) and the lowest in the N.I.B, fallow (2.5) and this was significant (p<0.05). There were no significant differences in pest infestations on the normal season crop (0.3) and the ratoon crop (0.6) p<0.05 and SRI and conventional irrigated fields (p<0.05). From the results it is recommended that off season planting of rice be discouraged and that efforts are made to ensure that farmers synchronize planting dates and other cultural practices for the crop, within the scheme and in rice farms outside the scheme.
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.