Soil fertility status and wheat nutrient content in Vertisol cropping systems of central highlands of Ethiopia
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Background: Land degradation reduces agricultural productivity and poses a serious threat on food security status of households. In Ethiopia, farmers have been using only urea and di-ammonium phosphate for more than 15 years. Several reports that indicate lack of response to these fertilizers, which could be due to limitation of nutrients other than nitrogen and phosphorus. Therefore, the present study was initiated to evaluate the soil fertility status of ten sites in central highlands Vertisols of Ethiopia and wheat nutrient content. Results: The physico-chemical properties of soils showed that the soils were clayey in texture, neutral to slightly alkaline (pH 7.2–7.9) and low to medium in their organic matter (1.6–3.2 %) content. Total N content was low in 100 % of the samples while 80 % of the soil samples showed P deficiency (<10 mg kg−1). Exchangeable K, Ca and Mg in all soil samples were high, while available sulfur was low. On the other hand, K to Mg ratio varied from 0.13:1 to 0.44:1, indicating Mg induced K deficiency. All soil samples were adequate when analyzed by ammonium bicarbonate diethylene tri-amine penta-acetic acid extractable Cu (>0.5 mg kg−1), Fe (>5 mg kg−1), and Mn (>1 mg kg−1) contents. However, 70 % of the samples were deficient in Zn (<1.5 mg kg−1) content. Mehlich 3 extractable B (<0.5 mg kg−1) and acid ammonium oxalate extractable Mo (<0.1 mg kg−1) were found to be low in all soil samples. The plant analysis data showed that all samples were low in N, P and K, while high in Ca and Mg concentrations. The deficiency of tissue K content was not predicted by the soil exchangeable K test. Plant micronutrient analysis showed that Cu, Fe, Mn and Cl concentrations were within the sufficiency range while Zn was deficient in all of the samples. Conclusions: Soil and/or tissue test results are indicative of deficiency of N, P, K, S, Zn, B and Mo that could be amended by fertilizer application, although more data are needed to thoroughly support this conclusion. The highest correlation (r > 0.90) between soil and plant nutrient content was observed for P, K, Mg, Cu, Fe, Mn and Zn, implying that flag leaves at flowering stage can be used to calibrate soil and plant contents for the deficient nutrients.
- Agriculture