Changes in Soil Chemical Properties Under Different Land-Use Systems and Soil Depth Layers: A Case Study from the Central Highlands of Ethiopia


 Background: Soil chemical properties have changed under different land-use systems and soil depth layers either by increasing or decreasing. Hence, scientifically information on the soil chemical properties dynamics under different land-use systems and soil depths are crucial for best land management practices, and to avoiding ecological negative impacts of it for sustainable development. The study aimed to evaluate the soil chemical properties dynamics under different land-use systems and soil depths in the central highlands of Ethiopia. The land-use systems included natural forest, four exotic tree plantation species (Eucalyptus globules, Cupressus lusitanica, Grevillea robusta, and Pinus patula), grassland, grazing land, and cropland. Results: The analysis of variance (ANOVA) for the majority of soil chemical properties of OC, TN, Avial. P, soil pH, EC, CEC, and exchangeable bases (Ca, Mg, K, Na) were showed that significant variations among land-use systems (P<0.0001). The highest mean values of OC (3.49 % DM ), TN ( 0.31 % DM) , Avail.P (31.52 mg/kg of soil ), CEC ( 33.63 meq/100gm soil), Exch. Ca (17.13 cmol(+)/kg soil), Exch. Mg (5.37 cmol(+)/kg soil), and Exch. K ( 3.60 cmol(+)/kg soil) were observed under natural forest than others of land-use systems. The results also showed that the lowest mean values of OC (1.47 % DM), TN (0.13 %DM), soil pH (5.38), CEC (18.98 meq/100gm soil), Exch. Ca (9.93 cmol(+)/kg soil), Exch. K (1.20 cmol(+)/kg soil), and Exch. Na (0.22 cmol(+)/kg soil) were recorded under cropland than other land-use systems. The highest mean values of EC (3.47ds/m), and Exch. Na (0.60 cmol(+)/kg soil) were observed under Eucalyptus globulus plantation forest. The overall mean values of OC, TN, Avail.P, CEC, Exch. Mg, Exch. Ca, Exch. K, and Exch. Na accumulation at the topsoil layer was higher than that of the subsoil layer except for soil pH and EC. Conclusion: In general, the majority of soil chemical properties under cropland and Eucalyptus globulus plantation forest were poorer than the soils subjected to other land-use systems which indicated that changes in land use systems were significantly affected soil chemical properties.

effects would be avoided. The study aimed to evaluate the soil chemical properties dynamics under different land-use systems and soil depths in the central highlands of Ethiopia.

Methods And Materials
Description of the study area Location A eld study was conducted in the central highland of Ethiopia, Oromia Regional State, Yerer forests, and surrounding area. Yerer forest is one of the remnant montane evergreen natural forest and plantation forests with different exotic tree species in the central highland of Ethiopia. The study area is located in the central-eastern part of Ethiopia at 40 km southeast far from Addis Ababa, and 17 km north of Bishoftu town. Yerer forest and surrounding areas is located between 8°52'00" − 8°55'00" N latitude and 38°59'30" − 38°95'15" E longitude, with altitudinal ranges between 2000 and 3105 m.a.s.l. (Fig. 1).

Climate
The 31 years meteorological data  showed that the mean annual rainfall of the study area is 907.33 mm which characterized by a unimodal rainfall having a long dry season (6-8 months), and the mean annual minimum and maximum temperatures were recorded 11.1 0 C, and 29.5 0 C, respectively National Meteorology Service Agency (2019). The farmers in the central highland of Ethiopia area are practicing ''mixed'' farming systems (i.e. both crop and livestock production activities).
The vegetation of the area Yerer Mountain natural forest is one of the remnants and secondary natural forests, which are categorized under the Dry evergreen montane forest in the central highlands of Ethiopia. Yerer Mountain natural forest is consists of natural forest and established plantation forests, and covers an area of 3254 ha of this 1793 ha is plantation forest with exotic and native tree species in monoculture and mixed forms, and 1461 ha is covered by natural forest and others.
Recently, plantation activities were carried out by different exotic and native tree species in, and surround the Yerer natural forest area. The major plantations of exotic tree species are Eucalyptus globulus, Cuppressus lustanica, Eucalyptus camandulensis, Pinus patula, and Grevillea robusta; however, the native tree species include Juniperus procera, Hagenia abyssinica, Podocarpus falcatus, Olea europaea subsp.cuspidata, and Cordia Africana.

Land-use systems
In the Yerer forest and its surrounding area, the major land-use systems are a natural forest, exotic tree plantation species forests, grassland, grazing land, and cropland. The land-use change started from 1991 and in the past two half decades in the central highlands of Ethiopia, pasture, and forest areas have decreased signi cantly, while arable cropland has increased proportionally due to the rapid population growth requires additional farmlands for food crop production. In the present study context de nition: Natural forest is the forest land that is composed primarily of the indigenous (native) tree, shrubs, lianas, climbers, and other herbaceous plant species, which may include both closed forest and open forest. Exotic tree plantation species is described as the forest stands established arti cially by non-native tree or shrub species in reforestation and afforestation program for industrial and non-industrial purposes. Grassland is an area where characterized as vegetation land dominated by the nearly continuous cover of grasses (Poaceae) family rather than large shrubs or trees species. Grazing land -is a land covered with grass or herbage and suitable for grazing or feeding by livestock or herbivore. Croplands is referring to land covered with temporary crops production both in single or multiple cropping systems, followed by harvest and leave a bare soil period.

Sampling Design
For the present study, eight (8) different land-use systems (LUSs) were selected, namely: natural forest, four exotic tree plantation species (Eucalyptus globules, Cupressus lusitanica, Grevillea robusta, and Pinus patula), grassland, grazing land, and cropland. In this study, the eight land-use systems were considered as treatments and the sample quadrats in each land-use system were considered as a replication. The systematic sampling design was used to determine the soil chemical properties with transect lines laid in each land-use systems (LUS). Four transect lines were delineated and laid parallel to each other along the altitudinal gradient in each land-use system separately for soil sample collection by using the 50-meter distance between two adjacent transect lines, and between the consecutive interval of quadrat on a transect line to avoid biased of samples selection.
Soil sampling procedure, data collection, and sample preparation For soil data collection of site selection from eight (8) land-use systems (LUS) were considered the relative similarity of each LUS as criteria in their topography, altitude, aspect, slope, and areas free from erosion exposed. For soil data collection the main square sample quadrat of 20 m x 20 m (400 m 2 ) area was established by systematic sampling techniques with twelve (12) replication quadrats in each land-use system. The soil samples were collected in ve replicates of subplots with 1 m x 1 m area within each a main square quadrat by placing four (4) subplots at each corner and one (1) subplot at the center of the main quadrat. The soil samples were collected close to the center of each subplot (1 m x 1 m area) by using a soil auger in adjusting with the required soil depth layers and by carefully cleaning the equipment at each soil sampling depths, to prevent soil contamination between different soil sampling layers and quadrats. The soil samples were collected at two soil depth layers; each layer is 20 cm thick at the topsoil layer (0-20 cm) and subsoil layer (20-40 cm) at the center of each sub-plot area.
The collected ve soil samples from each main quadrat were bulked /combined with respect to their similar depth layer categories and mixed well thoroughly to form a one representative composite soil sample per the main quadrat to reduce variability within a quadrat. Finally, 1 kg of the composited representative soil samples from each quadrat concerning each depth layer was packed into plastic bags and transport to soil chemical laboratory analysis. The collected representative soil samples were labeled with appropriate information and transport immediately to the soil laboratory of Hawassa University, Wondo Genet College of Forestry and Natural Resources, for sample preparation and laboratory analysis. Before the analysis, the composite soil samples were air-dried, ground, and sieved to pass through a 2 mm size sieve in preparation for laboratory analysis of most soil chemical properties. The soil samples were further sieved to pass through a 0.5 mm size sieve for the analysis of total nitrogen (Ranst et al., 1999).

Laboratory Analysis of soil chemical properties
The soil chemical properties analysis parameters include organic carbon, total nitrogen, C: N ratio, available phosphorous, soil pH, soil electrical conductivity, Cation exchange capacity, exchangeable bases (Ca, Mg, K, and Na), and Percent base saturation. The soil organic carbon (OC) was determined following the Walkley Black wet digestion method as described by Ranst et al. (1999). The total nitrogen level in the soil was determined following the modi ed Kjeldahl's digestion, distillation, and titration method as described by Ranst et al. (1999). The C: N ratio was determined by dividing the value of organic carbon to the total nitrogen corresponding to each soil sampling depths. The soil available phosphorus content was determined by following the Olsen procedure (Olsen et, al., 1954). The soil pH was measured by using a digital pH meter in a 1:2.5 soil to water supernatant suspension (Jackson, 1973, Van Reeuwijk 1992. The Electric conductivity of the soil samples was determined by using an electrical conductivity meter from 1:1 soil-distill water mixture (20 g of soil in 20 ml distilled water). The cation exchange capacity (CEC) of soils was determined by saturation with 1N sodium acetate followed by replacement of sodium on the exchange complex with 1N ammonium acetate at pH 7 following the procedure described by Chapman (1965). Sodium level was determined by atomic absorption spectrometry (AAS) and CEC expressed as meq/100 g of soils.` The exchangeable bases were extracted with 1M ammonium acetate at pH 7.0.
Exchangeable Ca and Mg were measured from the extract with an atomic absorption spectrophotometer; whereas exchangeable Na and K were determined from the same extraction with a ame photometer (Black et, al;1965). Percent base saturation (PBS) was determined by dividing total exchangeable bases (Ca, Mg, K, and Na) to the CEC of the soil and multiplies by 100.

Data Analysis
All quantitative eld soil data were analyzed by the General linear model (GLM) analysis of variance (ANOVA) procedure. Statistical difference in soil chemical properties among land-use systems and between soil depth layers was analyzed by a two-way analysis of variance (ANOVA) at p < 0.05 signi cant levels by using Statistical Analysis System (SAS) software (Version 9.4). A least signi cant difference (LSD) test was employed to assess the mean difference between soil variables. Means comparisons were used to soil properties change interpretation and explanation among eight land-use systems in the study area. Additionally, Pearson's correlation coe cient was employed to evaluate the relations of various soil chemical variables.

Results
Effect of land-use systems on soil chemical properties Soil Organic C, Total N, C: N ratio and Available P Soil Organic Carbon (%OC) The analysis of variance for organic carbon concentration of the soil revealed a signi cant difference horizontally as a function of land-use systems (p < 0001). The overall mean value of the organic carbon concentration under the eight different land-use systems (natural forest, four different exotic tree species plantation forest, grassland, grazing land, and cropland) was varied between 1.47 to 3.49%. Among the land-use systems (LUS) the highest concentration of organic carbon was observed in the natural forest, whereas in contrary the lowest concentration of organic carbon was observed in cropland ( Table 1,   Statistically, the total nitrogen content of the soil showed a signi cant variation as a function of land-use systems (p < 0.0001). The overall mean value of the total nitrogen levels in all different land-use systems varied between 0.13 to 0.22% ranges. Among the land-use systems, the maximum and minimum mean values of total nitrogen percent were recorded in natural forest and cropland in order of 0.31% and 0.13%, respectively ( Table 1, and Fig. 2).
Carbon to Nitrogen(C: N) ratio The C: N ratio shall determine by dividing the value of organic carbon to the total nitrogen corresponding to each soil sampling depths. The overall ANOVA analysis result revealed that there was a non-signi cant (p < 0.05) in uenced by any land-use systems. The overall mean value of the C: N ratio under eight different land-use systems were felled between the 11.38 to 12.08 ranges (Table 1).

Available phosphorus
The analysis of variance for available phosphorus revealed that there were signi cant differences (P < 0.0001) between all land-use systems except between Eucalyptus globulus and Cupressus lusitanica, and between Grevillea robusta and cropland. The overall available phosphorus concentration level under different land-use systems was observed in the range between 2.45 to 31.52 mg/kg of soil. Among the land-use systems (LUS), the maximum and minimum available phosphorus concentration were recorded in natural forest and Cupressus lusitanica plantation forest, respectively (Table 1,  Soil pH, EC (ds/m), and CEC Soil pH /Soil reaction Soil reaction or soil pH is one of the soil chemical properties that used to measure the acidity or alkalinity of the soil. The analysis of variance for soil pH revealed that a signi cant difference as a function of land-use systems (p < 0.0001) except between Eucalyptus globulus and Cupressus lusitanica. The overall mean value of pH in the soil under the different land-use systems was observed in the range between5.38 to 6.49. Among the land-use systems (LUS), the maximum and minimum pH in soil was recorded in grassland, and cropland, respectively (Table 1, and Fig. 2).

Soil electrical conductivity (EC)
Soil electrical conductivity (EC) is a measure of the number of salts in soil (salinity of soil). The statistical analysis for soil electrical conductivity revealed a signi cant variation among land-use systems (P < 0.0001) except between Eucalyptus globulus and cropland, between Grevillea robusta and Pinus patula, and between grassland and grazing land. The overall mean values of soil electrical conductivity (EC) distribution under different land-use systems were varied in the range of 1.78 to 3.47 ds/m. Among all land-use systems, the maximum and minimum mean values of soil electrical conductivity (EC) concentration were observed in Eucalyptus globulus plantation forest, and natural forest, respectively (Table 1, and Fig. 3).

Cation-Exchange Capacity (CEC)
The analysis of variance (ANOVA) for cation exchange capacity (CEC) was showed a signi cant variation among land-use systems (P < 0.0001) except between Pinus patula, grassland, and grazing land. The overall mean values of Cation-exchange capacity (CEC) distribution under different land-use systems were varied in the range of 18.98 to 33.63 meq/ 100 gm soil. Among all land-use systems, the maximum and minimum mean values of soil Cation-exchange capacity (CEC) concentration were observed in natural forest(33.63), and cropland (18.98), respectively (

Percent base saturation (PBS)
Percent base saturation (PBS) is determined by dividing total exchangeable bases (Ca, Mg, K, and Na) to the CEC of the soil and multiplies by 100. The analysis of variance (ANOVA) for percent base saturation revealed a non-signi cant difference with horizontal as a function of land-use systems, (at p < 0.05).
In the study area, the mean values of Percent base saturation (PBS) in all land-use systems (LUS) were recorded more than 70%. Among all land-use systems (LUS) the minimum and maximum Percent base saturation (PBS) were observed in Eucalyptus globulus(70.91%), and Cupressus lusitanica (80.83%) plantation forests, respectively (Appendix Table 2).
Effect of soil depth on soil chemical properties BS% concentration under all different land-use systems (natural forest, Eucalyptus globules, Cupressus lusitanica, Grevillea robusta, and Pinus patula, grassland, grazing land, and cropland ) across vertical gradients at the top layer were higher than the subsoil layer (Table 3, and Appendix Table 3). Keys: *, **, ***, and ns = signi cant at P < 0.05, high signi cant at P < 0.01, very high signi cant at P < 0.001, and nonsigni cant at P > 0.05, respectively.
The statistical analysis of variance (ANOVA) for soil electrical conductivity (EC), Cation exchange capacity (CEC), and exchangeable Mg (Exch. Mg) were revealed that signi cant variations between soil depths (P < 0.05). The overall mean value of soil Cation exchange capacity (CEC), and exchangeable Mg (Exch. Mg) concentration under land-use systems at the topsoil layer were higher than the subsoil layer. However, the analysis of variance for soil pH and C: N ratio was revealed that the nonsigni cance variations in between vertical gradients of soil depth at (p < 0.05). The overall mean value of soil pH, electrical conductivity (EC), and C: N ratio concentrations under land-use systems at the top layer were lower than the subsoil layer. In all land-use systems, the level of soil pH, electrical conductivity (EC), and C: N ratio trend between topsoil (0-20 cm) and subsoil (0-40 cm) layers were not uniformly distributed in the area (Table 3, and Appendix Table 3).

Discussion
Effect of land-use systems on soil chemical properties Soil Organic C, Total N, C: N ratio and Available P Organic matter has an important in uence on soil chemical properties, soil fertility status, plant nutrition, and biological activity in the soil (Brady and Weil, 2002). Among the different land-use systems, the organic carbon concentration levels were observed in the order of natural forest > G. robusta > grassland > P. patula > C. lusitanica > grazing land > E. globulus > cropland. The overall maximum mean value of the organic carbon concentration was observed beneath the natural forest (3.49% DM), and Grevillea robusta plantation forest (3.14% DM) statistical without signi cant differences between them, but signi cant difference from the rest six land-use systems. This probably due to the higher accumulation of soil organic matters (SOM) by adding litters to soils from different heterogeneity plant species with the high rate of biomass production, and better carbon nutrient release or mineralize to the soils through The total nitrogen concentration levels distribution trend horizontal as a function of land-use systems were registered in the order of natural forest > G. robusta > grassland > P. patula > C. lusitanica > grazing land > E. globulus > cropland. The highest mean value of total nitrogen content was observed in natural forest (0.31% DM) and followed by the Grevillea robusta plantation forest (0.26% DM), statistically with signi cant differences between them. This may be attributed to the long-term accumulation of above and below-ground organic matter inputs from litterfall, root turn over mineralization by actions of soil microbes, and N xation by symbiotic in leguminous plant species diversity in natural forest and other soil microorganisms. This argument is supported by the signi cant strong positive correlation (r = 0.947) between the total nitrogen and organic carbon. Similar studies were also reported as the higher total nitrogen content was observed in the natural forest than other land-use systems in different areas (Michelsen et The overall mean value of the C: N ratio in all land-use systems were statistically not signi cant differences between them. The C/N ratio was signi cantly narrowed from 11.38 in the natural forest soils to 12.08 in the Pinus patula plantation forest soils. The lowest value of the C: N ratio was observed in the natural forest. This may be attributed by the factor of increase nitrogen nutrient inputs with a high rate of nitrogen xation by different leguminous plant species diversity having a relatively higher protein and nutrient contents in the natural forest that leads to the lower C: N ratio, due to their fast decomposition rate and release of nitrogen to the soil. Faster decomposition of leaf litter enhances the transfer of fresh carbon to mineral soil (Polglase et al., 2000).
Similarly, different workers have been reported the lower C: N ratio under different native plant species diversity (Yadessa, 1997; Hailu 2000, and Yadesa, et.al. 2010). The highest value of the C: N ratio (12.08) was observed in the Pinus patula plantation forest. This may be attributed due to lower nitrogen content in the litters of organic matters which results in a higher C: N ratio, and slow decomposition rate. Plant residue with a low C/N ratio (high nitrogen content) decompose more quickly than plant residue with a high C/N ratio (high carbon content) and do not increase soil organic matter accumulation levels as quickly (Janssen 1996 In the present nding, the mean values of electrical conductivity (EC) of soil were found numerical between 1.78 and 3.47 deciSiemen per meter (dS/m) ranges. According to the current nding the mean value of electrical conductivity (EC) of soil levels across land-use systems was found in the order of E. globulus,> cropland > G. robusta > P. patula > C. lusitanica > grassland > grazing land > natural forest. The maximum mean value of electrical conductivity (EC) was observed in the Eucalyptus globulus plantation forest (3.47) and followed by cropland (3.07) without signi cant differences between them. For the higher value of EC under Eucalyptus globulus plantation forest may be attributed due to the lower soil moisture content that related with soluble salts accumulate in the upper soils rather than leached down, high evaporation rate due to open canopy, and low in ltration rate in combine resulting to dissolved salts are left behind to accumulate in the upper soils layer, salts originate from the disintegration (weathering) of minerals and rocks, soils with an accumulation of exchangeable sodium are often characterized by poor tilth and low permeability making high EC. This argument is supported by the positive correlation between the electrical conductivity (EC) and exchangeable sodium, Na (r = 0.202), and negatively correlated with organic carbon (r = -0.466). This result is in agreement with the ndings of Michelsen et al. (1996). However, for the high level of EC in cropland probably due to tillage intensity and land management practice, cropping system and nature, salt accumulation from commercial fertilizers, chemical contamination (from herbicide, insecticide, and fungicide use by farmers), erosion, runoff, animal manures (usually high tunnels), and compost were contributed to raising EC. Similar studies were reported that higher values of EC in cropland soils than others of land-use systems (Dhaliwal andSingh 2003, Gol 2009, Kaur and Toor, 2012).
The minimum mean value of electrical conductivity was observed in the natural forest (1.783) than the other land-use systems. The lower level of EC under natural forest probably attributed due to the higher accumulation of organic matters (litter deposition) that decomposed and release higher exchangeable cations (K, Ca, Mg) to the soils, which lead to reducing the salinity level and lowering the values of electric conductivity in the soils. This explanation is supported with the negative correlation between electrical conductivity and exchangeable cations K(r= -0.400), Ca(r = -0.532), Mg(r = -0.173), and organic carbon (r = -0.466). This nding is in agreement with a similar study report by Michelsen et al. (1996), and Gol (2009) who had reported that the lower mean value of electrical conductivity under natural forest than other land-use systems.
The mean values of CEC in the study area were found between 18.98 and 33.63 meq/100 gm of soil ranges. The overall mean values of soil CEC level distribution in different land-use systems were recorded in the order of natural forest > P. patula > grassland > grazing land > E. globulus > G. robusta > C. lusitanica > cropland. Among the land-use systems the highest concentration of cation exchange capacity (CEC) was registered in natural forest (33.63). This is probably in uenced by the high amount of organic matter accumulation, and high soil pH in the natural forest soils that lead to higher CEC. This means the CEC of soils is affected mainly by the amount and degree of decomposition of the organic matter. In general, the higher soil organic matter (SOM) is resulting the higher the CEC. Because most of the CEC is originates from the amount of SOM decomposition rate that entirely pH-dependent. This argument is  The lowest concentration of exchangeable cations of Na, K, and Ca, were recorded in cropland in the order of 0.21, 1.20, and 9.93 cmol(+)/kg soil, respectively.
However, the minimum mean value of exchangeable Mg was recorded in the Cupressus lusitanica plantation forest (2.91 cmol(+)/kg soil). This could be due to the low addition of organic matters from external factors and the removal of crop residuals from the cropland by harvesting maybe contribute to lower addition of the cations nutrients of Na, K, and Ca to soils. Another explanation for the lowest concentration of exchangeable Na, K, and Ca in cropland probably due to continuous intensive tillage and cropping systems facilitate to lower bulk density, lower CEC, higher porosity, and higher in ltration rate in soils could lead simply these cations nutrients of Na, K, and Ca were leached out down to the soil depth by water. Similarly, Duguma et. al. (2010), and Molla and Yalew (2018) were observed that the highest concentration of exchangeable Ca in cereal farmland than other land-use systems.
Among the land-use systems, the highest mean value of percent base saturation (80.83) was observed in the Cupressus lusitanica plantation forest. This probably due to the amount and nature of clay particles contents and low concentration of CEC, and low pH level in soils could be contributed to the existence of higher percent base saturation (PBS) under Cupressus lusitanica plantation forest than others land-use systems. Because of the amount and type of clay minerals are responsible factors for CEC in that both clay and colloidal organic matters (COM). This argument is supported by a signi cant negative correlation between the soils PBS and CEC (r = -0.300) and between PBS and pH (r = -0.050). Similarly, Kebede and Charles (2009) were suggested that clay and colloidal organic matters are negatively charged and can act as anions; as a result, these two materials can absorb and hold positively charged ions (cations). These ndings are in agreement with a similar study report by Nsabimana, et.al. (2008), who had reported the higher percent base saturation (93.7%) under Cupressus lusitanica plantation forest among others plantation forests in southern Rwanda.
The lowest mean value of percent base saturation (70.91) was recorded in the Eucalyptus globulus plantation forest. This probably due to the lower addition of organic matters that undergone decomposition and liberate low cations nutrients of Na, K, Ca, and Mg to soils that lead to lower percent base saturation under Eucalyptus globulus plantation forest than the others land-use systems. This explanation is supported by the positive correlation between percent base saturation and organic carbon (r = 0.262), and a negative correlation between PBS and pH (r = − 0.050 The study results indicated that the lower overall mean values of the C: N ratio (11.64), pH (5.80), and electrical conductivity (EC) (2.22) were observed at topsoil layers than that of the subsoil layers. For the lower value of C: N ratio levels at topsoil is probably due to the highly decomposed organic matter releases higher N-levels on the topsoil than the subsoil layers, thereby, the lowering C: N ratio occurred at the topsoil layer. Similar to this nding, Yadessa and Itanna (2001)and Hailu (2000) also found a lower C/N ratio at the topsoil than in the subsoil layers under different native woody plant species diversity on farmland. The lower values of EC at topsoil are probably due to the addition and accumulation of organic matters at the topsoil surface than subsoil surface that liberates exchangeable cations, thereby, reducing soil EC at the topsoil layer. On the other hand, the pH levels distribution trend in soil was increased gradually from topsoil to subsoil layers in Eucalyptus globulus plantation, Cupressus lusitanica plantation, Pinus patula plantation forests, grazing land, and cropland of land-use systems in the study area. The result of the higher value of soil pH at subsoil than topsoil layers probably due to the leaching of more soluble soil minerals and basic cations from topsoil to the subsoil layer. Similarly, Michelsen et al. (1996) and Zewdie & Olsson, (2008) was reported that the increment of pH values from topsoil to subsoil layers in Eucalyptus globulus and, Pinus patula plantation forest land-use systems in the Ethiopian Highlands.
With regarding a vertical gradient of soil depth the overall higher mean value of exchangeable cations of Na, K, Ca, Mg, and percent base saturation (%BS) concentrations were observed at the topsoil layers than the subsoil layer with signi cance difference. The distribution of exchangeable cations of Na, K, Ca, Mg, and percent base saturation (%BS) concentration were decreased vertical from the topsoil layer to the subsoil layer in all land-use systems. These probably due to the effect of higher organic matters depositions or accumulation from litters of woody, herbaceous residuals, animal manures, and crops residuals on farmlands that undergone decomposition and mineralized cations nutrients of Na, K, Ca, and Mg to soils then CEC play the roles to retain the released cations at topsoil from the decomposed organic matter rather than translocating them to the subsoil layer. Cations, such as K + , Na + , and Ca 2+ , can be adsorbed onto soil or organic colloids, making the cations available for plant uptake by preventing cation leaching