Characterization of organic and inorganic phosphorus in the highland plateau soils of Ethiopia

Abstract

Abstract Surface horizon samples from two Vertisols, an Andisol, and an Alfisol were collected from farmers’ fields, research station farms, and from uncultivated/ nonfertilized areas to characterize the organic and inorganic forms of phosphorus (P) in the highland plateau soils of Ethiopia using the Hedley soil P fractionation scheme. The total P values ranged from 226 mg‐kg‐1 in the Akaki Vertisol samples developed on alluvial deposits to 1570 mgkg‐1 in the Andisol samples, where the HCl fraction dominates the inorganic soil P pool. The Alfisol samples contained 400 mg‐kg‐1 of total P, with the NaOHand residual P being the dominant P fractions. The resin inorganic phosphorus (Pi) and bicarbonate Pi fractions generally accounted for less than 15% of the total P in all soils, and were positively correlated with organic C. The NaOH P fraction, which was most prominent in the surface horizon samples of the Alfisols, accounted for 4–15% of total P. The HCl P fraction, ranged from 1% in the Alfisols to 46% in the Andisols, and positively correlated with pH. All of the P fractions were negatively correlated with clay and extractable Al contents. The organic P (Po) fractions were positively related to organic carbon (C) and dithionate extractable iron (Fe). All samples collected from farmers’ fields showed a loss of P from the residual, and HCl fractions as compared to the uncultivated/nonfertilized samples. There is also a decrease in the labile P (resin Pi, bicarbonate Pi, and Po) fractions, except for the Akaki Vertisol samples. However, under research station management, the amount of labile P fractions either increased or remained at the same level as the uncultivated/nonfertilized samples, except for the Andisol. Addition of P fertilizer at the recommended rates to the Debre Zeit research station Vertisol appears to have resulted in a slight increase in the labile P and prevented loss of P from the HClP and residual P fractions.