Potassium fractions and availability for chickpea (Cicer arietinum) in Vertisols of north-west Ethiopia

Abstract

For a critical appraisal of the supplying power of potassium (K) and to predict bioavailable K, it is necessary to have knowledge on the fractions of K and evaluate soil test methods for plant nutrition. This research aimed to assess the forms of K and select a suitable extractant for chickpea (Cicer arietinum L.) nutrition on Vertisols of East Gojjam, north-west Ethiopia. Potassium fractions and bioavailable K extracted by chemical solutions was measured using flame photometry. The mineralogy of Vertisols was assessed by X-ray diffraction. The results showed that the fractions of K were significantly correlated to each other and regression analysis showed that 97.6% of the variability of NH4OAc-K was accounted by the HNO3-K and total K fractions, signifying their existence in dynamic equilibrium. The forms of K were correlated to K uptake by chickpea, suggesting the contribution of the fractions of K to plant nutrition. The high level of K in each form was associated with the illite-smectite clay mineral. The availability of K by ammonium bicarbonate-DTPA was best predicted (R2 = 0.61, p < 0.05) by chickpea uptake in comparison with Mehlich 3 and NH4OAc (R2 = 0.48 and 0.47, respectively). The weaker prediction of NH4OAc-K may be due to the presence of high fixing clays. Further research is necessary on a wide variety of soils and crop types to verify this result and select a suitable extractant for crops in local conditions.