Major limiting nutrients and lime requirement for bean production on three contrasting soils of Lake Victoria crescent agroecological zone
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Farmers in the Lake Victoria crescent mainly grow common beans on three soil types: Phaoezem, Cambisol and Umbrisol, but the yield is still below the genetic potential. Some farmers have used organic fertilizers (1.3%), manure (8.7%) (UBOS, 2006) and foliar sprays (Kabuga et al., 2015), but the response has not been realized due to low soil fertility and soil acidity. Two studies were carried out with two objectives, namely; (1) To determine the most limiting nutrients in Phoezem, Cambisol and Umbrisol for Phaseolus vulgaris L. production and (2) To determine the lime requirements for Phaseolus vulgaris L. production in Cambisol and Umbrisol. For the limiting nutrients study, a pot experiment was laid out in CRD with nine treatments; (i) Control (ii) Complete treatment, (iii) -N, (iv) -P, (v) -K , (vi) -Mg, (vii) -S, (viii) -Ca and (ix) -micro nutrients. Each nutrient treatment was assigned to three soil types, replicated three times, and the experiment was repeated twice. Common bean variety BAT 477 was used as a test crop. Numbers of leaves per plant and above ground biomass production were taken to measure the growth of beans. To determine the lime requirements, two soil types namely: Cambisol and Umbrisol were collected from two farmers and this was based on their low soil pH and Ca levels. The Lime Requirement was determined using titration method and titration curves were developed for each soil type. Results indicate that bean plants growing in Phaoezem yielded significantly (P < 0.05) greater aboveground biomass and number of leaves plant-1 than those grown in Umbrisol and Cambisol, respectively. Beans growing in the complete treatment had significantly (P < 0.05) more leaves than beans grown in the control, phosphorus and nitrogen omitted treatments. The number of leaves and above ground biomass in the complete treatment was similar to that of the nutrient omission treatments for K, Ca, Mg, S and micronutrients. Phaoezem has inherently greater fertility than cambisol and Umbrisol. Phosphorus is the most limiting nutrient for bean production followed by nitrogen in three soils investigated. Other nutrients such as: K, S, Ca, Mg and micronutrients do not limit bean production in the three soil types. To rise pH to 5.8, Cambisol requires 8.4 tonnes of Ca(OH)2 per hectare, while Umbrisol requires 5.2 tonnes of Ca(OH)2 per hectare. Therefore, field studies are necessary to determine the optimum rates for both organic and inorganic fertilizers on the three soil types. There is need to address soil acidity in Cambisol and Umbrisol through liming using the lime requirement equations determined in this study. To deal with soil acidity related problems, plant breeding programs should develop germplasms tolerant to Al toxicity and/ or low soil available phosphorus.