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Potassium deficiencies limit common bean (Phaseolus vulgaris L.) production in West Usambara, Northern Tanzania
Baijukya, Frederick P.
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Common bean (Phaseolus vulgaris L.) is the most important food grain legume crop in west Usambara highlands, but its yield remains below the potential largely due to nutrient deficiencies in the soils. To identify nutrients limiting bean production, on-farm diagnostic trials were carried out at nine farmer fields around Lushoto town in the short rainy season (vuli) from November 2013 until February 2014, though soil and leaf sample analyses. Bean leaf samples were analysed for macro and micronutrients, and the Diagnosis and Recommendation Integrated System (DRIS) was applied to rank nutrients according to their degree of limitation to bean production. The combination of different analyses indicated potassium (K) and phosphorus (P) deficiency as a major constraint for bean production in the Usambara Mountains. Soil analysis indicated deficiencies of the nutrients K and P and partly nitrogen (N), calcium (Ca) and magnesium (Mg). Bean growth and yield results revealed positive responses to fertilisers P and K. Analysis of bean leaf tissue indicated deficient nutrient concentrations levels for P, K and N when compared with critical nutrient concentration ranges. Application of P and K (and partially N) fertilisers increased leaf concentrations of the respective elements but depressed the concentrations of Ca, Mg andcopper (Cu). Ranking the obtained leaf nutrient concentrations with the DRIS approach, showed consistent results for nutrient deficiencies of P and K. Severe K deficiency became also visible at some fields through chlorotic and necrotic leaf symptoms. More work is required to establish the right combinations of deficient nutrients including establishing new fertilizer blends and their appropriate application rates.