Occluded phosphorus dominates in highly weathered soils of the Didessa toposequence, Western Ethiopia
Year: 2026
Type: article
Abstract: Ultisols, Alfisols and Vertisols of humid Western Ethiopia are deficient in bioavailable phosphorus (P) but information on their P reserves is largely lacking. This study quantified the P fractions of four soils (Ferrudalfs, Rhodudalfs, Hapludults, Hapluderts) from four land uses (arable, fallow, grazing and agroforestry) along a 53-km long toposequence in the Didessa watershed at the elevation of 1273–2700 m above sea level. Six P fractions (microbial-P, NaHCO 3 -P, NaOH-P, dilute HCl-P, concentrated HCl-P, and concentrated H 2 SO 4 -H 2 O 2 -P) were sequentially extracted, and Total P (TP) was separately determined. The mean inorganic NaHCO 3 -P was only 5.2 mg kg −1 but the mean TP was high (2020–3138 mg kg −1 ). The trend of TP along the toposequence was neither consistent with landscape positions nor degree of weathering. The sum of occluded and residual P was high both in quantity and proportion (73–80%). An abundance of sparingly soluble P has gradually been built up in these soils during pedogenesis likely as a consequence of leaching of silica and residual accumulation of Fe and Al oxides and P adsorbed onto them. The small proportion of labile P in all land uses and high proportion of more stable P suggest that the abundant recalcitrant P pools sparingly replenish the labile pools but rather scavenge the P released by weathering. This study challenges the pedogenic P depletion paradigm in highly weathered soils. • Phosphorus (P) in Ethiopian Ultisols, Alfisols and Vertisols was investigated. • All soils were rich in total P (2000–3100 mg kg −1 ). • About 80% of total P was found in occluded and residual fraction. • Occlusion is attributed as the process resulting in recalcitrant P accumulation. • This study challenges the pedogenic P depletion paradigm.
Source: CATENA
Authors: Abdenna Deressa, Markku Yli-Halla
Institutions: Wollega University, University of Helsinki
Language: English
Subfield: Waste Management and Disposal
Field: Environmental Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,680
OpenAlex ID: W7128448966