The variations in soil texture across land use types and slope gradients reflects the influence of anthropogenic activities and topographical process on soil formation and degradation. The higher sand content in eucalyptus plantations relative to natural forests suggests not only that these plantations are often established on previously degraded or erosion-prone lands, but also that their management practices (e.g., minimal understory and frequent harvesting) may exacerbate erosion and reduce finer particles such as silt and clay. Sandy texture on various types of land is likely the result of erosion’s selective removal of clay particles (Soto et al., 2019). This erosion process has led to the formation of sand in certain areas, causing the predominance of sand soil texture in eucalyptus plantations. This finding aligns with the observations of Tellen and Yerima (2018), who reported that on steep slopes (9%–15%), the mean sand fraction was higher (31.50%) compared to gentler slopes (0%–8%), which had a lower mean sand fraction (21.75%). This variation is likely due to erosion, which selectively removes finer soil particles and increases the proportion of coarser particles such as sand on steeper slopes. This finding aligns with the results of Selassie et al. (2015).

The lower clay content in eucalyptus plantations compared to forest land suggests that soil degradation and erosion processes have contributed to the depletion of finer soil particles. Natural forests, with minimal disturbance, tend to retain higher clay content due to better soil structure and organic matter accumulation. This is because natural forests typically have high levels of organic matter, which helps bind soil particles together, improving soil structure and stability (Chaikaew and Chavanich, 2017). This enhanced structure prevents clay particles from dispersing and eroding easily. In contrast, eucalyptus plantations often receive insufficient organic matter, leading to poorer soil structure and lower clay content (Fialho and Zinn, 2014). As a result, the soils in eucalyptus plantations generally have less clay compared to those in natural forests, due to the reduced input of organic matter that is essential for maintaining soil integrity (Osman and Osman, 2013).

Similarly, the variation in silt content across different land use types indicates the impact of land management practices. The higher silt content in cultivated land may be attributed to soil disturbance from plowing, which redistributes finer particles, while the lower silt content in eucalyptus plantations and grazing land suggests erosion-driven depletion of silt-sized fractions. These findings emphasize the need for effective soil conservation measures to mitigate erosion and preserve soil quality under different land uses.

The higher concentrations of clay and silt in areas with gentle slopes suggest reduced soil erosion and greater retention of finer soil particles. This is likely due to lower runoff velocity, which minimizes the selective removal of clay and silt fractions. In contrast, steeply sloping areas exhibit lower clay and silt content, indicating increased erosion and preferential loss of finer particles, leaving behind coarser soil fractions. Consequently, the impact of eucalyptus plantations on soil properties may be less pronounced in flatter areas, where clay content remains relatively stable. These findings align with previous studies highlighting the influence of topography on soil texture distribution, where steeper slopes are more prone to erosion-driven depletion of fine soil particles. The presence of clay and silt at different slope positions may be the consequence of upland silt and clay fraction deposition, which enriched the lower sloping area. A study by Zádorová et al. (2023), revealed similar results.

The higher bulk density observed in cultivated land suggests soil compaction due to continuous agricultural activities, including frequent tillage and machinery use, which reduce soil porosity. In contrast, the lower bulk density in forestland indicates minimal soil disturbance and higher organic matter content input from litterfall and root turnover, which enhances soil structure and porosity. These findings align with those of previous studies that have highlighted the role of land use in influencing soil physical properties. Intensive cultivation tends to increase bulk density because the soil surface is constantly exposed to the direct force of raindrops (Roth-Nebelsick et al., 2022), and the loss of organic matter degrades the soil structure, resulting in soil compaction (Grosbellet et al., 2011). This compaction reduced pore space and increased soil density. Therefore, the higher densities found in the soils of cultivated land were due to the constant exposure of the soil surface to raindrops and degradation of the soil (Vaezi et al., 2017).

This increase in bulk density may also have been attributed to an extended period of continuous cultivation. This study is consistent with previous findings, which reported that the bulk density of agricultural land use was higher than that of forest land use (Vaezi et al., 2017). This could be because of the greater organic matter content of natural forest as opposed to agriculture, which has a continuous removal of organic matter with less addition to cultivated land (Guimarães et al., 2013). The highest OM content causes a lower bulk density in the soils of natural forest land because OM has a very low density compared to mineral soil particles (Rühlmann et al., 2006). This lower bulk density in natural forest soils results in an improved soil structure and increased water-holding capacity (Acín-Carrera et al., 2013).

Variations in bulk density across slope classes suggest the influence of topography on soil compaction and porosity. The higher bulk density observed on the upper slope may be attributed to increased erosion and reduced organic matter accumulation, which led to soil compaction. In contrast, the lower bulk density on the lower slope could be due to greater organic matter deposition, reduced soil disturbance, and enhanced soil structure and porosity. These findings are consistent with previous studies indicating that bulk density tends to increase in areas with higher erosion rates and decrease in depositional zones where organic matter accumulation is more pronounced. These factors could be responsible for the variations in soil bulk density among the slope classes. The results obtained from this investigation correspond to the findings reported by Aytenew and Kibret (2016), who found that the bulk density of soils on steep slopes was highest at 1.41 g cm⁻³ as compared with gentle slopes at 1.32 g cm⁻³, which was caused by the high clay fraction, porosity, and minimal soil disturbance from erosion.

The higher total porosity observed in natural forests indicates an improved soil structure, primarily due to the accumulation of organic matter from continuous litter fall and minimal disturbance. Organic inputs promote soil aggregation and stabilize pore spaces, which are critical for maintaining soil aeration, water infiltration, and root penetration. In contrast, the lower porosity in grazing and cultivated lands may be a result of physical soil compaction caused by livestock trampling and repeated tillage operations. These disturbances degrade the soil structure, reduce macropores, and limit the movement of air and water within the soil profile, thereby affecting soil productivity and ecosystem functioning. This finding aligns with previous studies indicating that land use changes significantly affect soil porosity, with natural vegetation promoting better soil structure, whereas intensive land use practices lead to compaction and reduced porosity (Asmare et al., 2023). Implementing sustainable land management practices, such as reduced tillage and controlled grazing, could help mitigate soil compaction and improve soil porosity in cultivated and grazed lands.

The variation in total porosity across slope gradients suggests that soil structure and compaction are influenced by the topographic position. The lower total porosity observed in the upper sloping area (9%–15%) may be attributed to higher erosion rates, which remove finer soil particles and organic matter, leading to increased soil compaction. In contrast, the higher porosity in the lower sloping area (0%–8%) could result from the accumulation of eroded materials, which enhances the soil structure and creates more pore spaces. This result is similar to the findings of Hailemariam et al. (2023), indicating that soil porosity tends to decrease on steeper slopes due to the impact of erosion and reduced organic matter content, ultimately affecting soil water retention and aeration.

The lower soil pH observed in Eucalyptus plantations than in natural forests suggests that land use significantly influences soil acidity. The relatively higher pH in natural forests may be attributed to the accumulation of organic matter and nutrient cycling processes that help to buffer soil acidity. In contrast, Eucalyptus plantations influence the soil pH and chemical fertility through multiple pathways. Decomposition of acidic organic residues, such as leaf litter, releases organic acids, whereas rapid nutrient uptake by trees depletes base cations, contributing to acidification. Additionally, phenolic acids and volatile oils released from Eucalyptus leaves, bark, and roots can negatively affect neighboring plants (Birhanu and Kumsa, 2018). These compounds, along with increased soil erosion and leaching, exacerbate soil acidification and lower the overall soil chemical fertility. This outcome aligns with the findings of Koutika et al. (2014), who reported that eucalyptus plantations had significantly more acidic soil than other land use types. This increased acidity is likely attributable to the high levels of tannins and phenolic compounds present in eucalyptus leaves, which contribute to soil acidification. An additional explanation might be increased microbial oxidation, which results in organic acids and gives soil H⁺, which contributes to the overall increase in soil acidity (Bolan et al., 2023).

The variation in soil pH across slope positions can be attributed to differences in soil erosion, leaching, and organic matter accumulation. The higher pH observed in the upper slope may result from the selective removal of acidic components through erosion, leaving behind less acidic soil constituents. While, previous studies suggested that cations (Ca⁺², Mg⁺², K⁺, and Na⁺) and clay (OM) were removed from the top and deposited at the bottom slope position, there may be an accumulation of these elements along the lower slope gradient that is responsible for the higher soil pH values (Dessalegn et al., 2014). The loss of base-forming cations through leaching and runoff accelerates erosion, lowers the soil pH, and increases the soil acidity (Ma et al., 2018).

The lower soil organic matter (SOM) content in eucalyptus plantations than in natural forests suggests that land use changes significantly impact soil fertility. The reason for the highest SOM content in natural forests may be attributed to litter falling from trees and shrubs. Trees with large short roots are an important source of nutrients and SOM enrichment. A higher concentration of grass roots and detrital inputs of grass litter into the layers beneath the forest might have led to a higher amount of organic matter (OM) in the forest land (Van Der Sande et al., 2023).

Leaves falling from eucalyptus plantations have fewer management practices, and fewer inputs of organic substrate as fertilizer could contribute to the low SOM accumulation in these plantations (Versini et al., 2014). This result is consistent with Bewket and Stroosnijder (2003), who stated that in the Dangule area, the highest OM was recorded in forest land and the lowest in eucalyptus plantations. According to Ashagrie et al. (2005), the amount of organic matter present in the soil decreases when natural forests are converted into eucalyptus plantations.

The variation in organic matter (OM) content across different slope positions can be attributed to soil erosion and deposition processes. Lower-sloping areas tend to accumulate organic matter because of the downward movement of eroded soil and organic residues, leading to higher OM content. In contrast, upper-sloping areas experience greater erosion, which removes surface organic material and reduces the OM levels. This pattern aligns with previous studies by Selassie et al. (2015) and Aytenew and Kibret (2016), indicating that the slope gradient influences soil fertility, with lower slopes acting as deposition zones that enhance soil organic matter accumulation, while upper slopes are more prone to degradation and nutrient loss. Effective soil conservation measures, such as contour farming and vegetative cover, could help mitigate erosion and improve soil organic matter retention in upper slope areas.

The higher total nitrogen content in natural forest land use is due to continuous organic matter accumulation from diverse vegetation and minimal soil disturbance. In contrast, the lower total nitrogen content in eucalyptus plantations than in natural forests suggests a decline in soil fertility, likely due to the high nutrient demand and low organic matter input associated with eucalyptus trees. Eucalyptus species are known to rapidly absorb soil nutrients, which, combined with limited litter decomposition, can lead to nitrogen depletion.

This might be because it is probable that no residues will be able to return to the soil as organic matter, and that bacteria that decompose organic matter are hindered in strongly acidic soils. This prevents organic matter from decomposing, which leads to an accumulation of organic matter (SOM) and the binding of nutrients, especially nitrogen (Coonan et al., 2020). This could be a major factor leading to low levels of soil OM and TN, which negatively affects plant growth and soil fertility. This is similar to the findings of Mohammad and Adam (2010), who found that the total N content in forest land was the highest and that, according to the classification of Walkley and Black (1934), the total nitrogen content in the soils of cultivated, grazing, and eucalyptus plantation lands was the lowest. While the lowest in cultivated land may be the result of crop residues being collected for fuel, animal feed, and temporary construction, no residues can be returned to the soil (Alaminew and Desta, 2024). Sustainable land management practices, such as integrating organic amendments or mixed-species plantations, may help mitigate nitrogen depletion in eucalyptus-dominated landscapes.

The variation in total nitrogen (N) content across different slope positions can be attributed to the influence of topography on soil nutrient distribution. Lower slope areas tend to accumulate more organic matter, which is the primary source of TN and is resistant to water erosion, and the lower slope has a higher nitrogen content. The majority of stakeholders graze on these lands communally, which causes nitrogen and other nutrients to accumulate (Sinore et al., 2018). However, because of the increased erosion, nitrogen removal occurred on the upper slope. The finding of Wubie and Assen (2020), which showed that total nitrogen has an increasing trend from a moderately steep to a sloping gradient, lends additional credence to this. This could be due to their downward movement with runoff water from the higher slope gradient and accumulation at the lower hill gradient.

In contrast, the upper slope areas are more prone to erosion, which selectively removes topsoil and associated organic matter, leading to lower nitrogen levels. Effective soil conservation measures are essential for mitigating nutrient loss and maintaining soil productivity, particularly in upper slope regions.

The higher available phosphorus (P) content in cultivated land compared to other land use types is maybe due to the regular application of mineral fertilizers, particularly NPS and diammonium phosphate (DAP), aimed at enhancing crop productivity. These inputs directly increase soil P levels, especially in the surface layer, where they are most commonly applied. This results supports the findings of Guelfi et al. (2022), who reported elevated available P in intensively managed croplands. In contrast, Eucalyptus plantations exhibited the lowest available P content, which may be due to the absence of P fertilizer application and minimal soil management. Additionally, Eucalyptus species are know for their high nutrient uptake and potential to deplete surface nutrients over time, especially under monoculture systems (Gonçalves et al., 2017). This result is similar to that of Bewket and Stroosnijder (2003), who reported that the greater availability of P in cultivated fields than in forests suggests that trees in forests extract more phosphorus than field crops or that a high proportion of the P pool is retained and immobilized by microbes in the litter layers of forests and eucalyptus plantations. It is also possible that the use of cattle dung as a soil conditioner in cultivated fields has a significant impact (Ndzeshala et al., 2023). According to Dagnachew et al. (2019), cultivated land use had higher available P (8.04ppm) than other land uses, possibly due to the use of organic fertilizers (e.g., compost, manure, and household wastes) and inorganic fertilizers [e.g., urea (CO(NH₂)₂) and diammonium phosphate (DAP)] on the cultivation land.

The primary factors determining the amount of available phosphorus (P) are soil organic matter (SOM) and landscape position. The removal of P from the upper slopes and its accumulation in the lower slope positions suggests that runoff transports soil particles enriched with P downslope, leading to higher concentrations in lower gradient areas. This outcome is consistent with the findings of El Kateb et al. (2013), who reported that lower landscape positions have higher available P than other positions. Similarly, Zebire et al. (2019) explained that this phenomenon occurs because of the accumulation and downward movement of SOM at lower elevations, resulting in a higher available P.

Generally, according to Landon (2014), selected soil chemical characteristics in the study area, including pH, total nitrogen (TN), and SOM, range from highly acidic to moderately acidic. TN and SOM were moderate across all land uses types, whereas available P was classified as moderate based on Landon’s (2014) ratings. Effective soil conservation measures, such as contour farming and vegetative cover, are essential to minimize P loss from the upper slopes and enhance soil fertility sustainability.

The variation in cation exchange capacity (CEC) across different land use types can be attributed to differences in soil organic matter (SOM) and clay content. Natural forests exhibited the highest CEC, particularly in lower slope areas, likely because of the accumulation of organic matter and the presence of finer soil particles, which enhance the ability of the soil to retain and exchange nutrients. Eucalyptus plantations had the lowest CEC, primarily due to poor undergrowth, deforestation for charcoal, and firewood production, which reduced soil organic matter. As a result, the Eucalyptus plantations had a significantly lower CEC than the other areas. Land use and human activity are responsible for this decline in soil organic matter (SOM), ultimately leading to a negative impact on soil fertility and ecosystem health (Ramesh et al., 2019).

This outcome is comparable to the findings of Rezaei et al. (2015), where clay content and high availability of soil organic matter may be the causes of CEC variation across slope gradients. Although the upper slope had the lowest CEC, erosion led to the removal of clay and soil organic matter (SOM), which aligns with the findings of Ellerbrock et al. (2016). According to Landon (2014), CEC values were rated as medium, Whereas the PBS value in natural forest land use was classified as high. In contrast, for cultivated, grazing, and eucalyptus land use, PBS was rated as moderate. This indicates that vegetation cover can reduce soil erosion, which is supported by the findings of Sun et al. (2013). However, it is also important to consider other factors that contribute to soil erosion.

The higher exchangeable Ca²⁺ content observed in natural forest soils than in eucalyptus plantations suggests that land use plays a crucial role in shaping soil nutrient availability. Natural forests typically have higher organic matter inputs through leaf litter and root turnover, which contribute to the replenishment and retention of base cations such as Ca²⁺. In contrast, the lower exchangeable Ca²⁺ levels in Eucalyptus plantations may be associated with accelerated nutrient depletion due to rapid growth of species, high biomass accumulation, and a deep rooting system, which extracts nutrients from deeper soil layers. Additionally, Eucalyptus trees are known to contribute to soil acidification through the accumulation of acidic litter and organic acids, which can displace Ca²⁺ from the exchange complex and increase leaching. These findings are consistent with previous studies (Demessie et al., 2012), where there is a greater likelihood of leaching downward by runoff and water percolation through no vegetation cover and fewer management activities practiced. This could result in less nutrient retention and a greater potential for erosion in eucalyptus plantations.

The variation in exchangeable Ca²⁺ across different land use types and slope gradients can be attributed to soil erosion and organic matter dynamics. The higher exchangeable Ca²⁺ content in the lower slope of the forest suggests the accumulation of leached nutrients and organic matter due to the downslope movement of soil materials. Forested areas generally contribute to higher organic inputs, which enhances cation retention and nutrient availability.

Conversely, the lower exchangeable Ca²⁺ observed in the upper slope of the eucalyptus plantations may be linked to erosion-induced nutrient loss and reduced organic matter input. Eucalyptus plantations are often associated with lower soil fertility owing to their susceptibility and the possibility of easy downward leaching by runoff from the upper slope of eucalyptus plantations, as well as the association of biological accumulation with the biological activity of plant residues from the upper slope and deposition in the lower slope of the natural forest. This is in line with the findings of Tamene et al. (2020), who reported that deforestation, leaching, limited recycling of dung and crop residues in the soil, and erosion have contributed to the depletion of exchangeable Ca⁺², Mg⁺², K⁺, Na⁺, and CEC on steep slopes of agricultural lands.

The strong positive correlation between exchangeable Ca²⁺ and cation exchange capacity (CEC) suggests that soils with higher Ca²⁺ levels tend to have greater nutrient retention capacity, which enhances soil fertility. Additionally, the positive correlation between exchangeable Ca²⁺ and soil organic matter (SOM) indicated that organic matter plays a crucial role in maintaining calcium availability. Soil organic matter (SOM) is one of the most prevalent basic cations near colloidal soil surface. The recorded exchangeable base values are believed to be insufficient to restrict crop growth and productivity. Instead, other factors such as nutrient availability and soil management practices may play a larger role (Thomas et al., 2007). Conversely, the significant negative correlation between exchangeable Ca²⁺ and sand content suggests that sandy soils, which have lower CEC and a limited ability to retain nutrients, tend to have reduced calcium levels. Similarly, the negative correlation with bulk density (BD) implies that compacted soils may restrict calcium availability, potentially owing to reduced porosity and impaired root penetration. These findings highlight the importance of maintaining organic matter content and managing soil texture to sustain soil fertility and nutrient availability.

The maximum percentage base saturation (PBS) was found beneath the upper slope of a natural forest, accounting for 72.89% of the interaction effects between land use type and slope. This is because natural forests have low H⁺ concentrations and exchangeable cation accumulations (van Der Heijden et al., 2013). The degradative effect of eucalyptus plantations on soil properties, the removal of basic exchangeable cations, and the high concentration of H⁺ all contribute to decreased PBS (Kebebew et al., 2022). The lowest mean value of PBS was found under the upper slope of eucalyptus plantations, This aligns with the reference (Selassie et al., 2015). Although there is numerical variation, the main effect of slope did not significantly affect the percent base saturation value. This suggests that the slope of eucalyptus plantations does not have a significant impact on the percent base saturation value.