G.N. Karuku

Influence of Selected Ecological Farming Practices on Soil Moisture Retention and Yield of Sorghum (Sorghum bicolor (L.) Moench) and Cassava (Manihot esculanta Crantz) in Semi-Arid Yatta Sub-County, Kenya

In this study, the influence of ecological farming practices on soil moisture and yield of cassava (Manihot esculanta Crantz) and sorghum (Sorghum bicolor (L.) Moench) was investigated. The study was conducted in semi-arid Katangi and Ikombe divisions of Yatta sub-county between October 2010 and August 2012. A randomised complete block design with a split plot arrangement was used. Main plots were three cropping systems: (i) Intercropping; (Dolichos [Lablab purpureus]/Cassava, Dolichos/Sorghum, Pigeon pea [Cajanus cajan (L.) Millsp.]/Sorghum, Pigeon pea/Cassava); (ii) Rotation; Dolichos-Cassava, Dolichos-Sorghum, Pigeon pea-Cassava, Pigeon pea-Sorghum and (iii) Monocrop (pure cassava and sorghum). Split plots were organic inputs; farm yard manure (FYM), compost and absolute control. Sorghum/pigeon pea intercrop+FYM treatment had high moisture levels during short rain season (SRS) of 2010 at Katangi (5.21%), SRS of 2011 at Ikombe (5.19%) and long rain season (LRS) of 2011 at both sites (5.83%, 12.30%). Grain yields were highest under sorghum/dolichos intercrop+ FYM during LRS of 2011 at Katangi (1.36 t ha-1) and Ikombe (1.48 t ha-1), and SRS of 2010 at Katangi (1.39 t ha-1) only. Cassava/dolichos intercrop recorded high soil moisture levels in both sites under sorghum/dolichos intercrop during SRS of 2010 (6.48%, 8.35%), LRS of 2011 (7.63%, 8.77%) and LRS of 2012 (6.41%, 3.65%) for Katangi and Ikombe, respectively. Tuber yields were higher under cassava/pigeon intercrop in Katangi (18.63 t ha-1) and Ikombe (28.73 t ha-1) during SRS of 2010 and LRS of 2011, and SRS of 2011 and LRS of 2012 at Katangi (20.86 t ha-1). Intercropping sorghum with dolichos and cassava with pigeon pea + FYM would be a viable strategy to boost crop yields in smallholder farming systems of Yatta sub-county.

Assessment of soil nutrient balances in organic based cassava (Manihot esculenta Crantz) and sorghum (Sorghum bicolor (L.) Moench) cropping systems of Yatta Subcounty, Kenya.

Long-term food production in developing countries is under threat due to soil nutrient mining resulting from unsustainable production practices. In this study, the sustainability of various cropping systems and organic input combinations were assessed through monitoring nutrient flows and balances at crop production level. The study was conducted in Katangi and Ikombe divisions of Kitui sub-county between October 2010 and August 2012. A randomised complete block design with a split plot arrangement was used. The main plots were three cropping systems: (i) Intercropping (Dolichos [Lablab Original Research Article American Journal of Experimental Agriculture, 4(12): 1557-1578, 2014 1558 purpureus]/Cassava, Dolichos/Sorghum, Pigeon pea [Cajanus cajan (L.) Millsp.]/Sorghum, Pigeon pea/Cassava); (ii) Rotation (Dolichos-Cassava, DolichosSorghum, Pigeon pea-Cassava, Pigeon pea-Sorghum); (iii) Monocrop (pure cassava and sorghum). The split plots were; farm yard manure (FYM), compost and control. All crops had above ground biomass incorporated after harvest in the same plot they were harvested from. Nutrient flows; nitrogen (N), phosphorus (P) and potassium (K), were monitored for four seasons; short rain season (SRS) of 2010, long rain season (LRS) of 2011, SRS of 2011 and LRS of 2012 using NUTMON toolbox. There were no significant differences in nutrient balances between the four seasons except in sorghum based cropping systems where N and P balances were significantly lower in the second year. Losses across the seasons occurred mainly through harvested products in both sorghum and cassava cropping systems while addition mainly occurred through biological N fixation and incorporation of crop residue. Negative NPK balances were found in cassava than sorghum-based cropping systems regardless of legumes used in both sites. Dolichos rotation with sorghum and compost applied resulted in positive N balances. Dolichos-cassava rotation with compost also had reduced N losses compared to when pigeon pea was used. P losses were less negative under pigeon pea-sorghum and pigeon pea-cassava rotation with FYM applied. Pigeon pea rotation with sorghum and FYM applied resulted in reduced K losses while with cassava the same cropping system was superior but with application of compost. The choice of legume and organic input for use would depend on environment farmer operates in. In N, P and K limited environments; dolichos rotation with compost application, pigeon pea rotation plus FYM and, pigeon pea-sorghum rotation plus FYM and pigeon pea-cassava rotation with compost applied would, respectively, be recommended as farming practices.

Nitrogen Mineralization Potential (No) in Three Kenyan Soils, Nitisols, Ferralsols and Luvisols

Nitrogen mineralization potential is important so as to prevent over-fertilization that could lead to groundwater contamination or under-fertilization that could lead to poor nutrient provision by crops leading to low yields. Three soil types were selected on the basis of groups, agro-ecological zone, organic matter content and land use. The soil samples were taken from the 0-15 and 15-30 cm depth. The samples were placed in incubation bags, water added to field capacity, sealed and incubated in laboratory at room temperature. The bags were opened at intervals of two weeks and soil sub-samples taken for analysis of mineral N for a period of 17 weeks. The calculated mineralizable N was 138.8 μg N and 116.4 μg N/g for Gituamba andosols, 46.0 μg N and 46.4 μg N/g for Kitale ferralsol and 260.1 μg N and 197.3 μg N/g soil for Katumani luvisols in the 0-15 and 15-30 cm depth, respectively. These calculated values compared well with the actual cumulative mineralizable N for Gituamba andosols at 127 μg N and 74.1 μg N/g, for Kitale ferralsols at 48.0 μg N and 64.1 μg N/g and for Katumani 80.6 μg N and 47.7 μg N/g soil in the 0-15 and 15-30 cm depth, respectively. The time taken for 50% of potentially mineralizable N to be mineralized (t½) ranged from 6.3 weeks for Katumani luvisols 15-30 cm to 30.1 weeks for Kitale ferralsols 0-15 cm soil depths. The soils with highest rate constant (k) had the least. For example, 15-30 cm depth of Katumani luvisols with of 6.3 weeks had the highest k of 0.112 week-1 compared with Kitale ferralsols 0-15 cm depth with t½ of 30.1 weeks and the lowest k of 0.023 week-1. The observed data indicates that 50% of N would be mineralized in all the soil types with the exception of Kitale ferralsols (0-15 cm depth) within the growing period of the crops which is approximately 20 weeks.

Farmers’ perspectives on factors limiting tomato production and yields in Kabete, Kiambu County, Kenya

ABSTRACT A survey was carried out in Kabete, Central Kenya to establish the limitations and constraints experienced by farmers growing tomatoes. A structured questionnaire was prepared and tested in the field before the actual survey was carried out. Fifty farmers were interviewed and the data analysed established that most farmers lacked enough land, irrigation water, credit and technological knowledge to enable them to optimize tomato production, especially during dry spells when they could fetch premium prices. The average farm size ranged from 0.13 to 1.5 ha and ownership was on a freehold basis. Most households (43%) consisted of five people. A major constraint facing farmers was soil moisture, cited by 50% of farmers interviewed. Nematode infestation and low fertility came second at 25% each. About 60% of the farmers used diammonium phosphates (DAP) for planting and 20% top dressed with calcium ammonium nitrate (CAN). In conclusion, there is a need to provide farmers with reliable irrigation water at affordable prices and credit facilities to enable them to afford inputs such as quality seeds and fertilizers. This will allow them to produce in the dry seasons to take advantage of premium market prices.