Variation in soil acidity across different land uses, soil types and altitudinal gradients in Western Oromia, Ethiopia
Abu Regasa, Wassie Haile, Girma Abera
Abstract
Soil acidification is a critical global challenge that threatens agricultural productivity by limiting nutrient availability and degrading agroecosystems. In Ethiopia, a significant portion of arable land suffers from soil acidity, particularly in the mid and highland areas, posing serious constraints on crop yields. Assessing soil acidity extent across different land uses, soil types, and altitude gradients is essential for managing its spread and mitigating its impact on agroecosystems. This study examined the variation in soil acidity across land uses (coffee farms vs. croplands), soil types (Nitisols vs. Cambisols), and elevation (1500–2346 m.a.s.l.) in the Sayo District, western Ethiopia. A total of 78 composite soil samples (48 from Nitisols and 30 from Cambisols) were collected and analyzed for selected physicochemical properties. Results showed that with increasing elevation, soils became sandier (sand content rose from 31.7 to 47.5% in Nitisols) and less fertile, with clay content, organic matter (OM), total nitrogen (TN), and available phosphorus (Av. P) all declining. Soil pH decreased significantly with altitude indicating greater acidity (dropping from 5.47 to 4.86 in Nitisols and from 5.58 to 5.21 in Cambisols), while exchangeable acidity and aluminum toxicity increased, especially in croplands. Bulk density also rose with altitude and was higher in croplands (1.28–1.29 g/cm 2 ) than in coffee farms (1.13–1.16 g/cm 2 ), reflecting compaction from cultivation. Coffee farms consistently maintained higher OM (5.50–6.00%), TN (0.28%), Av. P (6.47–11.14 mg/kg), and cation exchange capacity (CEC) greater than in croplands due to organic inputs and reduced soil disturbance. Nitisols had lower sand content, pH, and Av. P, but higher clay content and exchangeable acidity than Cambisols. The significant interaction between elevation and land use underscores how both factors jointly intensify soil acidification and fertility decline. These findings highlight the urgent need for sustainable soil management strategies to mitigate acidification, enhance productivity, and preserve agroecosystem resilience in mid and highland farming systems.