Comparison of Yields of Paddy Rice Under System of Rice Intensification in Mwea, Kenya

The world population continues to grow fast, leading to an increased need for more food production. With the growing scarcity in water resources, there is an ever-greater challenge of sustainably producing more food to meet the food demand. Rice is the foremost staple food for about 50% of theworld’s population and is currently the food crop that requires the most water for its production. There is an upward shift in demand for rice worldwide due to urbanization, as people change their eating habits [28]. In Kenya, rice is the third most important cereal after maize and wheat. With the continuing population growth, Rice production in Kenya is now based mostly on the conventional practice of continuously flooding paddy fields . This method is not sustainable due to the alreadyexisting competition for water among farmers within and outside the Mwea irrigation Scheme. Thus, innovative ways for improving the efficiency of water use are imperative for sustainable rice production. Mwea Irrigation Scheme, where the research was conducted, is situated between longitudes 37°13’E and 37°30’E and latitudes 0°32’S and 0°46’S. The region is classified as tropical with a semi-arid climate, having an annual mean air temperature of 23-25°C with about 10°C difference between the minimum temperatures in June/July and the maximum temperatures in October/March. Annual rainfall ranges from 356mm to 1626mm with an average of 950mm, and annual sunshine of 2485h. The Scheme covers an area of 9,000ha, with a potential for 4,000ha expansion. The soils here are classified as Vertisols [38]. Currently, the Scheme accounts for 80% of the country’s rice production. The scheme is divided into 5 sections covering 60 units in total. Two rice crops are grown annually, the main season occurring between August and December during the short rains, with a longrains crop grown between January and June. Mwea producers suffer from water shortages during the main growing season and often from blast attack during the long rains season, factors that lead to reduced rice yields in both seasons. Other benefits of rice beside income generation for farmers include employment both on farms and in the market. Rice is very important to the livelihoods of Mwea people, with wider economic and food-security implications for Kenyans. The System of Rice Intensification (SRI), developed in Madagascar over 25 years ago, offers an opportunity to improve food security through increased rice productivity by changing the management of plants, soil, water and nutrients while reducing external inputs like fertilizers and herbicides . The system recommends the use of single, very young seedlings with wider spacing, intermittent wetting and drying, use of a mechanical weeder which also aerates the soil, and enhanced soil organic matter-SRI recommends addition of organic manure, thus boosts organic content of the soil. All these practices are aimed at improving the productivity of rice plants grown in paddies through healthier, more productive soil systems and plants that are supported by greater root growth and by nurturing the abundance and diversity of soil organisms. Previous research has shown yield increases of between 50- 100% while irrigation water inputs can be reduced by between 25% and 50% with SRI. However, little is known about the effectiveness of SRI practices, and the impact of their adoption on yields and water savings, under Kenyan conditions. This study investigated within the Mwea irrigation Scheme, which has the most concentrated production of rice in Kenya, whether SRI practices — particularly transplanting quickly one young seedling per hill, alternate wetting and drying, and wider spacing — could have significant effects on plant growth and subsequently on grain yield and water productivity..

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