There are various avenues for intensifying agricultural production, the most common being increased use of fertilizers, supplemental irrigation of crops, and adoption of high-yielding varieties. These options are rather widely known to farmers around the world, but they have not been widely adopted by smallholders in subSaharan Africa. The low adoption rate is related to complex technical and socio-economic issues, such as poor extension services, lack of capital, failure to mobilize the requisite water, or simply, poverty. The System of Rice Intensification (SRI) is in a special category of innovation in that, farmers stand to gain multiple benefits from its use, including the possibility of increasing rice yields substantially, saving water, and getting better grain quality, using differently the assets that they already have. A major impediment for the adoption of SRI in Africa has been lack of knowledge about this intervention, especially for farmers already practicing irrigated agriculture. Farmers generally have good business sense and will adopt technologies or practices once the benefits are proven and the risks are seen as minor. SRI should be attractive for these reasons, but there are various issues to be resolved before large numbers of farmers can adopt the method. This article reports on the steps taken and the technical and socio-economic issues addressed in efforts to introduce SRI and promote it in Kenya, specifically in the Mwea Irrigation Scheme. A diverse set of individuals and institutions in Kenya together embarked on the evaluation and dissemination of SRI methods in this East African country beginning in July 2009. If the new methods can perform in Kenya as in other countries, this will bring much benefit to rice farmers and rice consumers in the region. SRI is coming to Kenya relatively late, as it was the thirty-ninth country from which favorable SRI results have been reported. This means that Kenyans can learn from others' experience and evaluations, and there is also now more of a supportive institutional framework. The initial results from on-farm SRI trials have been positive, although not conclusive. They have given impetus to Kenyan farmers and institutions to collaborate within a multi-sectoral, multilevel coalition that has provided an informal, multi-faceted platform for the evaluation, adaptation and dissemination of SRI practices. The initiative in Kenya is now gaining more formal status and more resources. This experience is presented to show the kinds of things that have been and can be done to utilize the SRI opportunity for raising land, labor, and water productivity in the rice sector.

Effects of change in weather conditions on the yields of Basmati 370 and IR 2793-80-1 cultivated under System of Rice Intensification (SRI) in Mwea and Western Kenya irrigation schemes were assessed through sensitivity analysis using the Ceres rice model v 4.5 of the DSSAT modeling system. Genetic coefficients were determined using 2010 experimental data. The model was validated using rice growth and development data during the 2011 cropping season. Two SRI farmers were selected randomly from each irrigation scheme and their farms were used as research fields. Daily maximum and minimum temperatures and precipitation were collected from the weather station in each of the irrigation schemes while daily solar radiation was generated using weatherman in the DSSAT shell. The study revealed that increase in both maximum and minimum temperatures affects Basmati 370 and IR 2793-80-1 grain yield under SRI. Increase in atmospheric CO2concentration led to an increase in grain yield for both Basmati and IR 2793-80-1 under SRI and increase in solar radiation also had an increasing impact on both Basmati 370 and IR 2793-80-1 grain yield. The results of the study therefore show that weather conditions in Kenya affect rice yield under SRI and should be taken into consideration to improve food security.

A study was carried out at Karima Village in the Mwea Rice Irrigation Scheme in Kenya to assess the impact of rice husbandry and associated land cover change for mosquito larval abundance. A multi-temporal, land use land cover (LULC) classification dataset incorporating distributions of Anopheles arabiensis aquatic larval habitats was produced in ERDAS Imagine version 8.7 using combined images from IKONOS at 4m spatial resolution from 2005 and Landsat Thematic Mapper (TM)trade mark classification data at 30-meters spatial resolution from 1988 for Karima. Of 207 larval habitats sampled, most were either canals (53.4%) or paddies (45.9%), and only one habitat was classified as a seep (0.5%). The proportion of habitats that were poorly drained was 55.1% compared with 44.9% for the habitats that were well drained. An LULC base map was generated. A grid incorporating each rice paddy was overlaid over the LULC maps stratifying each cell based on levels of irrigation. Paddies/grid cells were classified as 1) well irrigated and 2) poorly irrigated. Early stages of rice growth showed peak larval production during the early part of the cropping cycle (rainy season). Total LULC change for Karima over 16 years was 59.8%. Of those areas in which change was detected, the LULC change for Karima was 4.30% for rice field to built environment, 8.74% for fallow to built environment, 7.19% for rice field to fallow, 19.03% built to fallow, 5.52% for fallow to rice field, and 8.35% for built environment to rice field. Of 207 aquatic habitats in Karima, 54.1 (n = 112) were located in LULC change sites and 45.9 (n = 95) were located in LULC non-change sites. Rice crop LULC maps derived from IKONOS and TM data in geographic information systems can be used to investigate the relationship between rice cultivation practices and higher anopheline larval habitat distribution.

<p>Lowland irrigated schemes contribute the most rice produced in Kenya. However, production is low and highly variable due to management problems. Production could be increased with appropriate soil management which requires that baseline fertility status of the soils and how they vary be known. This study examined the variability of selected soil chemical properties in the Mwea Irrigation Scheme in Central Kenya. Soil samples were collected from the top 0-15 cm depth in August 2013 and 2014 and analysed for pH, electrical conductivity (EC) and the exchangeable cations potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺) and sodium (Na⁺). Significant variability in soil EC as well as soil cation concentration was observed among units. Overall results showed soil pH ranged from 4.56 (very strongly acidic) to 8.05 (moderately alkaline). Soil EC varied from 0.17 to 1.52 dS m^-1 with higher elevation areas recording lower values (&lt; 0.50 dS m^-1) and lower elevation areas recording higher EC values (&gt; 0.50 dS m^-1). On average, exchangeable Ca²⁺ was 38.17 cmol_c kg^-1, Mg²⁺ 23.80 cmol_c kg^-1, Na⁺ 1.24 cmol_c kg^-1 and K⁺ 0.35 cmol_c kg^-1. The soil exchange complex was mainly dominated by Ca²⁺ and Mg²⁺ and cation concentration in the soil was in the order Ca²⁺ &gt; Mg²⁺ &gt; Na⁺ &gt; K⁺. Soil K is low and severe cation imbalances exist with regard to K⁺ and other cations thus making K⁺ deficient for plant uptake. Management practices and farming systems which enhance soil K status should be encouraged to help boost and sustain rice yield.</p>

Soil degradation reduces agricultural productivity and poses a great threat on food security status of households. In Kenya, farmers have for a long time been using only nitrogen and phosphorous based fertilizers oblivious of the soil fertility status. In most cases, there has been lack of plant response to these fertilizers, which could be due to a limitation of nutrients other than nitrogen and phosphorous. Soils are considered as variable natural bodies because of combined intrinsic and extrinsic factors of different intensities at a field or a larger region scale therefore an understanding of such variability is imperative to provide insights needed in their management. This study was thus initiated to assess the availability of soil micronutrients from rice growing Vertisols in the Mwea irrigation scheme. Top (0-15 cm) soil samples were collected across paddy fields in the irrigation scheme and analyzed for iron (Fe), zinc (Zn), copper (Cu) and manganese (Mn) by the 0.1 N HCl extraction method. Soil pH (water and 1 M KCl) was also measured using the glass electrode pH meter. Soil solution pH ranged from 4.56 to 8.05 and 3.33 to 6.63 for water and 1 M KCl respectively. Soil Fe, Zn, Cu and Mn concentration varied greatly and ranged from undetected to 1360.6, 0.12 to 8.00, undetected to 9.29 and 1.50 to 849.2 mg/kg respectively. Coefficient of variations (CVs) for soil micronutrients ranged from 64% to 154% indicating very high variability. Soil pH was least variable with CVs 12% and 15% for water and KCl respectively. These results imply that the paddy soils in Mwea region are highly heterogeneous and soil micronutrients are enriched in some areas and depleted in others due to farm management practices and soil properties. Averagely, soil available Zn was deficient across the scheme and as such Zn fertilization can be effective in increasing soil Zn concentration and availability in the soil-root interface further enhancing soil productivity and yield quality. Attention should also be paid to appropriate farm management practices to avoid accumulation or depletion of nutrients.