Assessing the Spatial Variability of Soil Acidity in Assosa District, Northwestern Ethiopia

Soil acidity negatively affects agricultural productivity, biodiversity, and food security in the tropical and subtropical regions. It exhibits significant spatial variability arising from natural soil‐forming processes and anthropogenic factors. This study aimed to analyze the spatial variability of soil acidity, develop digital maps of acidity levels, and characterize selected soil properties related to acidity in cultivated land. A total of one hundred georeferenced composite surface soil samples were collected using multistage, stratified, and random sampling techniques. Samples were analyzed for pH in both H 2 O and KCl solution, soil organic matter (SOM), cation exchange capacity (CEC), exchangeable acidity (EA), exchangeable aluminum (EAl), and soil texture. The results showed that the soil pH in H 2 O ranged from 5.06 to 6.60 (mean 5.56), while the pH in KCl ranged from 3.95 to 5.17 (mean 4.43). The consistent acidity across both measurements, with a mean ΔpH of approximately 1.13, indicates that the soils are predominantly acidic, likely due to significant levels of Al 3+ and H + ions on the exchange sites. Geostatistical analysis identified the Gaussian model as the best fit, with a spatial range of 18.95 km, well above the average sampling distance of 3.2 km. Ordinary kriging showed that soil pH variation was moderately influenced by intrinsic soil properties and external environmental or management factors. The resulting spatial map classified the study area into three soil acidity levels: strongly acidic soils (38.2%, ∼49,606 ha), moderately acidic soils (38.4%, ∼49,830 ha), and neutral soils (23.4%, ∼30,397 ha). The generated soil acidity map provides baseline information and can serve as a valuable tool to develop targeted management strategies for soil acidity. Future studies should focus on periodic assessments of soil acidity and its spatial variability in the study area, along with detailed mineralogical analyses to support precision agriculture and optimize acid soil management.