Soil Micronutrient Status and Iron and Zinc Availability for Haricot Bean Production in Southern Ethiopia

Abstract

The study was conducted to assess micronutrients status and evaluate the availability of zinc and iron for haricot bean production in soils of Taba, Huletegna Choroko, Tenkaka Umbulo, Kontela, Alage and Jole Andegna, southern Ethiopia. Soil profiles were opened, and soil samples were collected from each horizon to analyze pH, organic carbon, cation exchange capacity, and available micronutrients. A greenhouse experiment was conducted in soils collected from the above sites using the following treatments:  no fertilizer; application of N and P; application of N, P and Zn; application of N, P, and Fe; application of N, P, Zn and Fe; application of Zn only; application of Fe only. Sources of Zn, Fe, N and P were ZnSO₄.7H₂O (21% Zn), FeSO₄.7H₂O (20% Fe), urea and TSP, respectively. Haricot bean variety Nasir was planted in a pot filled with 5 kg soil. ZnSO₄∙7H₂O and FeSO₄.7H₂O were sprayed on the leaves, and urea and TSP were applied to the soil just before planting. Four haricot bean seeds per pot were sown and, later, thinned to two seedlings. Grain yield, plant height, number of pods per plant and number of seeds per pod were collected. Leaves and seeds were analyzed for micronutrients using Microwave Plasma Atomic Emission Spectrometer (MPAES).The soils of the study areas have different textural classes varying from sand to clay with pH>7.4. Iron (Fe), zinc (Zn) and copper (Cu) were low in Tenkaka Umbulo and Huletegna Choroko soils whereas manganese (Mn) was high at the surface and low in subsurface horizons. In Taba soils, Cu was deficient throughout the profiles whereas Fe, Zn and Mn were high in the surface and low in subsurface horizons. Soils of Jole Andegna contained low Fe, and high Cu and Mn whereas Zn content was high in the surface but low in the subsurface horizons. Application of Zn with NP significantly increased grain yield compared to the no fertilizer treatment. Application of Fe and Zn either alone or combined with NP produced significantly higher tissue concentrations of the minerals than the other treatments. Therefore, fertilization of haricot beans with Fe and Zn is important in the soils of the study sites especially for quality production in terms of Zn and Fe in seeds.

Keywords: Fe concentration, Haricot bean, NPZnFe, Zn concentration, micronutrients