Characterization of soils under major land uses in Chencha District , South Ethiopia

Assessing land use induced changes in soil properties is essential for addressing the issues of land use planning and sustainable land productivity in highlands of Ethiopia. The surface and profile soil samples were collected from forest (FL) cultivated (CL) and grass/pasture lands (GL) in Doko Yoyira (DY), Aiezo Tula (AT) and Gendona Gembela (GG) in Chencha district, Gamo-Gofa zone in May 2014, which aims to assess different soil physicochemical properties. At surface layer of 0-20 cm, the results did not show any significant difference (P<0.05) for land uses and sites. However, differences were noticed for land uses and sites in terms of certain soil characteristics determined on soil profile basis. The cultivated soils contained less soil organic carbon and total nitrogen compared to forest and grasslands. Hence, forest and grassland systems could maintain organic carbon and nitrogen stocks in the soils. The findings have implications for developing sound land use policy to combat on ongoing soil degradation in the area.


INTRODUCTION
Ethiopia's economy is chiefly agricultural with more than 80% of the country's population employed in this sector.This is constrained by the deteriorating natural resource base, especially in the highlands where 80% of the population lives (Abera and Belachew, 2011).Soil degradation in the form of plant nutrient depletion is the major agro-ecosystem problem in these areas.Previous studies showed that negative nutrient balances mainly carbon, nitrogen and phosphorus indicating that soil is already mined (Lemenih, 2004).
Rapid increase in Ethiopia population demands more production of food, fodder, fiber and fuel from the land.
To meet these needs, vast tracts of land are being put under intensive cropping, and large areas of grasslands are being overgrazed and degraded in highlands of Ethiopia.Furthermore, widespread poor agricultural activities, including intensive tillage, complete removal of crop residues, low levels of fertilizer application, lack of appropriate soil conservation measures and cropping practice are also contributing factors (Haile et al., 2014).Agricultural activities change the soil chemical, physical, and biological properties, and play the major *Corresponding author.E-mail: waaqsh@yahoo.com.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License role for soil degradation mainly due to soil fertility decline as a result of lack of nutrient inputs.Soil resources degradation resulting from different causes threatens the long-term productivity.Nowadays, soil degradation reduces yield significantly.As a result, the communities are faced with challenges which affects all spheres of social, economic and political life of the population.It is one of the major challenges to development and food security of the country (Kassa et al., 2013).The goal of land manager should be to maintain nutrient levels in the range desirable for optimal plant growth but low enough to avoid environmental contamination (Erkossa and Teklewold, 2009).
In permanent agricultural systems, soil fertility is maintained through application of manure, other organic materials, inorganic fertilizers, lime and the inclusion of legumes in the cropping systems, or combination of these.In many parts of the world, the availability, use and profitability of inorganic fertilizers have been low whereas there has been intensification in land-use and expansion of crop cultivation to marginal soils.As a result, soil fertility has declined and it is perceived to be widespread, particularly in Sub-Saharan Africa including Ethiopia (Abera and Belachew, 2011).
Management of the fertility of soils and their dynamics due to land use changes to preserve soils for the next generation and for their most effective use is essential to understand their nature and properties.In Gamo Gofa zone currently, information is lacking for farmers and extension workers on soil fertility status and nutrient management particularly in Chencha district.
The study aims to characterize the soil physicochemical properties under different land uses, landscapes for optimum production using the major soils to come up with the data for researchers and development workers and the interpretations can be applied for decision-making processes such as soil-plant management planning in agro-ecological conditions which is paramount importance for sustained production, and thereby improving the livelihood of small scale farmers and emerging investors on agriculture in the area.

Climate and soil resources
The rainfall regime of Chencha district is bimodal.The first round of rain occurs between March to April.The second round of rain occurs from June to August.The annual rainfall distribution in the district varies between 27 to 1412 mm (NMA, 2015).The minimum temperature in the district varies between 12 to 14°C, while the maximum temperature is in the range 20 to 24°C (Figure 2).The soils of the district are primarily clay or clay loams which have evolved from volcanic rocks (basalt) and volcanic tuff in the higher altitudes of the study area.The principal soil types are Cambisols and Nitosols (FAO, 1990).

Soil collection and analysis
Three households were selected with adjacent land uses (FL, CL and open GL) on the same soil types.For the purpose of this study, the three households were considered as replications, whereas the three land use types were considered as treatment.Barley and wheat are the two small sized seed annual crops that need intensive land preparation.Farmers have been applying inorganic fertilizer like urea and Diammonium phosphate (DAP).Organic fertilizers like compost and manure are more largely used for cereal crop production than inorganic fertilizers.Enset, apple crops are perennial crops often sole planted around their homestead.This land use is located closed to homestead, hence it received large amount of fresh manure and household wastes (Personal communication).
Nine soil profiles (three land uses x six soil depths replication) were dug and sampled in the FL, CL, and GLs with dimension of 2 m x 2 m x 2 m.Soil samples were collected from six soil depths: 0 to 2 m based on horizontal color differences in lower soil horizons under each land uses.In addition, three replications of surface soil (0-20 cm soil depth) from CL, FL and GL from higher, medium and lower slops using soil auger were sampled following hexagonal design at six points.
For each land uses, surface soil samples were sent for chemical analysis.Only nine composite surface and forty eight soil profile samples were used for chemical analysis.In addition from similar undisturbed soil samples, soil core samples were collected opposite to each pit for determination of soil bulk density and moisture contents.Thereafter, intact soil samples were collected with a manual core sampler of 10 cm height and 7.2 cm diameter, from each land use practice for soil moisture and bulk density determination.Soil-water content was determined by standard procedures described for gravimeter, with oven drying to a constant weight at 105°C for 24 h.Approximately, 1 kg of sample from each soil depth were collected and sent to laboratory then air-dried at  Bouyoucos (1962) hydrometer method (Andres et al., 2014).Water holding capacity was determined by the method (Wilke, 2005).
The amount of pore space or porosity of the soil is calculated according to the following equation: Bulk density (Db) = mass of dry soil / total volume of soil and air (g/cm3).Particle density (Dp) = mass of dry soil / volume of soil particles only (air removed) (g/cm3): (1) Db was calculated by dividing the weight of oven-dried soil with the volume of the core.Db of land uses were conducted at Arba Minch University, Civil Engineering Soil Laboratory.Total nitrogen content was determined following the Kjeldahl method (Okalebo et al., 1993).The available phosphorus (Av.P) content of the soil was analyzed using 0.5 M sodium bicarbonate extraction solution (pH=8.5)following Olsen method (Okalebo et al., 1993).The organic carbon determination was made following the wet oxidation method (Walkley and Black, 1934).The sieved and stored samples were analyzed for pH in 1:2.5 soils to water ratio using the pH meter.Electrical conductivity (Ec) was measured in water as soil to water ratio of 1:5.Multiplying organic matter by 0.58 was used to estimate organic carbon (Perie and Ouimet, 2007).Cation exchange capacity (CEC) was determined using Chapman method (Reak et al., 1990).Amounts of Ca 2+ and Mg 2+ in the leachate were analyzed by atomic absorption spectrophotometer.K + and Na + were analyzed by flame photometer.Composite samples were sent for physico-chemical analysis at JIJE Analytical Testing Service Laboratory, Ethiopia.

Statistical analysis
All data were statistically analyzed using the Analysis of Variance (ANOVA) procedures and also the general linear model (GLM) procedure of SAS 6.12.Means separation was done using least significant difference (LSD) (SAS Institute, 1998).

Impact of land use on soil properties of surface soil
Physical properties of soils of the sites (DY, AT and GG) sampled from surface soils (0-20 cm) are presented by land uses.Physical soil parameters: water holding capacity (WHC %), Db, soil porosity (SP) and soil texture (ST), did not show any statistically significant difference among land uses (Table 1).The results also indicated that chemical properties; pH, CEC, available K, TN, OC and C: N did not show significant differences among land uses at 0 to 20 cm soil depth (Table 2).Except soil clay contents, sand and textural classes at AT and GG at GG sites results showed that land use changes and their associated management practices could not cause significant changes in soil physical parameters under both land uses in lower soil horizons (Table 3).

Doko Yoyira site
Results showed that land use changes and their associated management caused significant changes on soil Ec, pH, Av.K and P, Na, Ca, Mg, OC, TN and C: N ratio.However, land use changes did not show effect on soil CEC (Table 4).Ec of the site rated as very low under for both cultivated forest and grazing land use systems might be due to excessive leaching of exchangeable bases.
The mean value pH of FL was lower (16.7%)than CL and GL.Numerically, CL and FL had lower CEC in comparison to GL by 2.72 and 18.97% in that order.Furthermore, FL showed the slightly lower CEC in both sampled land use which was rated as medium in the soils.The reason might be due to medium organic matter     This might be due to additions of organic and inorganic fertilizers under CL use systems.
Results depicted that Ca showed significant variation among land uses (Table 4).Ca content in soils was lower under FL (76.14%) and GLs (44.18%) than CLs (Table 4).The variation with Mg followed a similar pattern with that of Ca in the site.Mg content in soils of the site was lower under FL (87.11%) and GLs (45.19%) than CLs (FL<GL<CL).Mg under FLs was significantly lower (76%) than GLs (P<0.05).Ca content of the soil was low in the site.The reason might be excessive leaching, low contribution of litter fall for decomposition and high uptake of this nutrient by plant species which was confirmed with results reported by Limenih ( 2004) under E. species than CL.According to Landon (1991), value of Ca under FL was rated as low, Ca under CL was high; and Ca under GL was medium which was similar to report made by Ridvan and Orhan (2010).The mean value of Ca content under CL was similar with results reported by Niguse et al. (2012).The mean value of Ca contradicts the report gotten by Chimdi et al. (2012) in Western Ethiopia.
Mg content in the soil was also low in the site.This result might be due to little contribution of litter by mixed E. species into soil and excessive leaching caused lower Mg content under FLs.This result was comparable with findings made by Niguse et al. (2012) in Southwestern Ethiopia.Findings made by Yitbarek et al. (2013) on the other hand contradicts this result which showed an increasing order of Mg under FLs>GLs>CLs.As far as the rate of Mg is concerned, Landon (1991) stated that content of Mg in the soil was low under FL, medium under GL and high under CL use systems.These might be due to the application of organic and inorganic fertilizes than FL and GLs.Furthermore, the reason might be due to high leaching and low inputs of plant biomasses as leaf litter under FL and excessive GL by livestock under GLs.Results in Table 4 depicted that Na contents of soils showed significant variation among land use systems.Content of Na in the soil declined from GL, CL and FLs in order of 0.18, 0.16 and 0.11cmol/kg soil.Na contents of the soil demonstrated significant variation between FL and GLs; and the results also showed significant variation between FL and CLs.
According to Landon (1991), Na contents under these land uses were rated as deficient in the soil.The reason might be due to excessive leaching and soil erosion in the site.Na content in the site showed similar results with findings made by Niguse et al. (2012).The mean value of Av.P content did not show significant difference among the land use systems in the site.In both land uses, the value of available P was found to be in decreasing patterns of GL < FL < CLs.
The result of Av.P in the soil was low under FL and GLs but medium available P under CLs (Landon, 1991).The reason might be application of organic and inorganic fertilizers under CLs.This might also be due to excessive leaching, erosion and problem fixation of P in the site.The result of Av.P was similar with findings made by Kebede and Yamoah (2009).According to Landon (1991), soil organic matter (SOM) was very low both under FL and CLs.The reason might be due to low incorporation of organic matter (OM), root exudates and microbial decomposition and erosion hazard under these land systems.The trends of these results are in line with the findings gotten by Yitbarek et al. (2013), Chimdi et al. (2012) and Abera and Belachew (2011).
Average value of TN in the site did not show significant variation between CL and GLs (Table 4).The reason for the reduction of total N in the soil continuously CLs could be attributed to the rapid turnover (mineralization) of the organic substrates derived from crop residue (root biomass) whenever intensive cultivation are added.Soil TN in the site was very low under CLs; and low under FL and GLs.The reason might also be due to low application of OM, leaching and runoff hazard under both land use systems.The results showed comparable results with some of the findings made by Limenih (2004).
Narrower C: N ratios have sufficient N to supply the decomposing microorganisms and also to release N for plant use.Thus, both mean value under FL, GL and CLs showed sufficient N to supply the decomposing microorganisms and release N to soil plant use.Results in SOC status of the soils were influenced by different land use systems.The highest SOC was measured under FL (1.62) followed by GL (1.09) and CLs (0.64).Significant differences in TN content of soils were also observed among different land use systems.The mean value of soil TN under land uses showed lower under CL (50%) and GL use systems (19%) as compared to that of FLs.Significant differences in C:N ratio of soils also showed similar trends with SOC and TN among different land use systems.Therefore, results indicated that average C:N ratio of soil under land uses were lower under CL (28%) and GL use systems (17%) compared to that of FLs (Table 4).The result of C: N ratios under CL was rated as low.This might be due to higher decomposition OM which was facilitated by intensive cultivation.This is in agreement with findings made by Jesse et al. (2011) and Yitbarek et al. (2013) who reported that cultivation alters humus content and thus narrows the C: N ratio.

Aiezo Tula site (AT)
The effect of land use systems on Ec showed no significant difference among land uses.However, Ec Different letters show significant differences according to least significant differences test (LSDs) at P<0.05.
under GLs was relatively higher than CL (50.0%) and FLs (50%) (Table 5).According to FAO (1976) cited in Ahmed et al. (2013), the mean value of Ec rated as very low might be due to excessive leaching of exchangeable bases.This result agrees with findings made by Kebede and Yamoah (2009).
The results depicted significant variation among land uses in CEC content of the soils (Table 5).Effect of land use systems on pH of the soils did not show significant difference among land uses.It was higher under FL than CL (4%) and uncontrolled GL (0.68%).According to Foth and Ellis (1997), pH of the soil both under land uses was rated as moderately acidic.This result is in line with the findings made by Itanna et al. (2011).
Results of CL showed lower value in CEC than FL (58%) and GLs (15%).The average value of CEC in the site did not show significant variation between CL and GLs, and showed in overall significant results among land use systems.The result might be due to the decreas in SOM under GL and CLs.Results showed CEC under FL was rated as very high in medium CEC under CL and GL use systems (Foth and Ellis, 1997).The mean values of CEC under GL and CL were in line with findings made by Chimdi et al. (2012).Furthermore, findings made by Limenih ( 2004) showed similar mean value of CEC under FLs.
The average value of Av.K, Na and Av.P also showed significant variation among land use systems (Table 5).Though the average values of Na were insignificant, the highest value in the soil was recorded under FL relative to CL and GL uses.According to Landon (1991), the value of Na content in the soil under both land uses were low.This might be due to low input of OM, leaching, erosion and excessive tillage under CLs.Similar increasing trends in the soil from CL to GL then to FLs uses were observed in Na contents in the soil.Similar results were also reported by Chimdi et al. (2012) and Yitbarek et al. (2013).
Av. K in the soil was rated as high under FLs.This might be due to high OM added to forest floor in the site.On the other hand, mean value of Av.K under GL was medium and low under CLs (Foth and Ellis, 1997;Landon 1991).The reason might be due to overgrazing, leaching and soil erosion under GLs.The value of Av.K under GL was similar to findings made by Chimdi et al. (2012).The value of Av.K under CL land showed comparable results with findings made by Abera and Belachew (2010).
The mean value of Av.P in the soil was rated as high under FL, medium under CL land and low under GL use systems (Landon, 1991).The reason for the deficiency of Av.P under GL might be due to additive effect of erosion, leaching and overgrazing by livestock.Addition of organic matter under FLs and application of organic and inorganic fertilizers under CL use systems might increase Av.P. The mean value of Av.P showed comparable results with findings made by Tilahun (2007) under GL and Yitbarek et al. (2013) under CLs.The present result in Av.P under FL was also comparable with findings reported by Yitbarek et al. (2013).
Results in ANOVA showed that mean value of Ca content in soils showed significant variation among land uses (Table 5).When the average value of Ca in the soil within the land uses was considered under CL and GLs but did not significantly vary with Ca content of soils.However, CL and GLs showed significant variation under FLs.The average value of Ca under FLs (11.9) showed the highest in comparisons to CL (5.2) and GLs (7.7).Mg content in the soils showed similar trend to that of Ca in sites under different land uses.According to Landon (1991), the mean value of Ca content in the soil was high under FL, medium under both CL and GLs.This might be due to Ca that is easily susceptible to leaching than other exhalable bases like Na and K.The present result is in line with the findings made by Tilahun (2007) and Yitbarek et al. (2013) under FLs.Rate of Ca content in this study showed similar results with findings made by Chimdi et al. (2012) under GLs, Kiflu and Beyene (2013) under CLs and Jamala and Oke (2013) under FL and CL uses.
ANOVA showed significant variation among land uses in Mg contents.When the average value of Mg in the soil within the land uses was considered under CL and GLs there was no significant variation in the site.However, CL and GLs present significantly vary with Mg content of the soils from FLs in the site.The average value of Mg under FLs (7.70) was very high in CL (3.0) and GLs (5.04) (Table 5).The mean value of Mg content in the soil was high under both land use systems due to Mg that might be resistant to leaching and the addition of animal manure under GL; input of leaf litter, root exudates under FLs and application of organic fertilizers (compost and animal manure) under CL use systems.Other studies showed similar results of Mg content under CLs (Belachew and Abera, 2010).Results in SOC content showed significant variation among land use systems.SOC under FL depicted significant variation between CL and GLs.But, SOC did not show significant variation between CL and GLs.Average value of SOC in the site indicated from 5.05, 0.86 and 0.54 in decreasing order for CL <GL < FLs (Table 5).According to Landon (1991), SOC was rated as medium under FL, very low under CL and GL use systems.This result might be due to low input of organic matter, excessive tillage specific to CL and soil erosion.Findings made by Chimdi et al. (2012) illustrated similar results with present mean value of SOC under FL uses.Other studies, for example Belachew and Abera (2010), Tilahun (2007) and Haile et al. (2014) reported similar results in SOC under CL and GL use systems.
Similar trends were also observed in average value of TN with SOC among land uses.The average values of TN also showed insignificant difference between GL and CLs (Table 5).However, soil TN did not show significant variation between CL and GLs.Mean value in soil TN under CLs was lower than FL by 77% and GLs by 10%.Results of C: N ratios in the soil showed significant variation among land use systems.Although C:N ratio showed significant variation among sampled land uses, it did not show significant variation between CL and GLs.FLs (13.0) of the site showed the highest average value of C:N ratio of all in comparison to CL (5.5) and GLs (6.2).
The mean value of TN was rated as very low under CL, low under GL and medium under FL use systems (Landon, 1991).The reason might be due to erosion, leaching, and low input of organic matter (OM) under GL and CL than FL.Findings made by Tilahun (2007) showed similar results with mean value of TN under CL and GL uses.TN in the site indicated comparable results with report made by Amir et al. ( 2010) and Chimdi et al. (2012) under both land use systems.It might be due to decomposition of organic matter in the soil and released into the soil for the plant up take.This is similar to findings made by Tilahun (2007) under FL, CL and GL use systems.

Gendona Gembela Site (GG)
In this study, value of Ec showed insignificant variation among land use systems (Table 6).However, results in average values pH, CEC, Av.K, Ca, Mg, Na, Av.P, SOC, TN and C: N ratio showed significant variation among land use systems.The mean value of Ec was rated as very low under both land use systems (FAO, 1976cited in Ahmed et al., 2013).This might be due to low exchangeable bases.The present results show similar results with findings made by Tilahun (2007) under similar land use systems.Other report by Ayalew and Beyene (2012) was comparable with this study with respect to Ec under CLs.The pH of the soil was lower under CL than FL and GLs by 7.2 and 11.2% in that order.Results showed that mean value of pH was moderately acidic under FL and CL uses (Landon, 1991).On the other hand, pH under GL was rated as slightly acidic.The reason might be due to the characteristics of litter inputs from C. lusistanica.
Consequently, litter inputs of the species are decreasing the pH of the soil.Leaching, erosion effect on exchangeable bases and application of N fertilizers for a long period of time under CLs might also cause the decline in pH of the soil.The results were comparable to findings reported by Yitbarek et al. (2013) in Ethiopia.Results in CEC indicated significant variation among land use systems.However, when average value in CEC between FL and GLs was considered, it did not show significant variations.GLs in GG showed significant variation between CL and FLs.
Results in CEC showed significant variation among land use systems.However, when average value in CEC between FL and GLs was considered, it did not show significant variations (Table 6).GLs in GG showed significant variation between CL and FLs.In this study, CEC under GLs showed increasing trends by 26 and 28% than FL and GLs .The mean value of CEC was rated as medium under CL and FLs, and high under GLs (Landon, 1991).The lower CEC under CL as compared to GL and FLs might be due to low input in OM (Limenih, 2004).The increase in CEC under GL might be due to the application of OM in terms of animal manure.This result is in line with the finding made by Yitbarek et al. (2013) under GLs, but CEC under FL and CL were higher than the present value of CEC.
Soil Av.K was found to be significantly affected by land uses, however within land use systems Av.K did not show significant variation between CL and GLs.It was found to be largest (0.61) in soils under CL uses whereas generally become small under FLs (0.15) and GL (0.49) (Table 6).According to Landon (1991), the mean value of Av.K was rated as low under FL, medium under CL and GL use systems.The reason might be due to leaching of K under C. lusistanica plantation.The mean value of Av.K showed similar results with findings made by Yitbarek et al. (2013) and Belachew and Abera (2010) under CL and GL use systems.The results also showed similar results with findings made by Gebrelibanos and Hassen (2013) under both land use systems.
Results demonstrated that Ca contents under FL (8.07) and CLs (5.77) were significantly lower in Ca contents than under GLs (15.87) (Table 6).However, there was no variation with Ca between FL and CLs use systems.Value of Ca in the soil under GLs had clear significant variation from CL and FL use systems.According to Landon (1991), content of Ca in the soil was rated as high under GL and medium both for FL and CLs.The reason might be due to an input of animal manure, left over of crop residue and weed thrown from CL on GLs (personal observation).The reason might be due to intensive tillage and removal of crop resides under CLs which ultimately improved nutrient cycling of the soil through litter decomposition.Low input of Ca by C. lusistanica and Ca leaching under FLs (Limenih, 2004).This result was similar with several studies (Chimdi et al., 2012;Yitbarek et al., 2013;Asrat et al., 2014) under both land use systems.
Results in Mg content showed significant variation among land uses, whereas Mg did not show any significant difference between FL and CL uses (Table 6).Similar to Ca, average value of Mg also showed an increasing trend of GL>CL >FL by 6.50, 4.24 and 3.67 in that order.In this study, soil Na also showed similar trend with soil Ca and Mg contents under land uses which were indicated in the order of 0.25, 0.09 and 0.08.Under both land use systems, content of Mg in the soil was rated as high, whereas Na content in the soil was classified into low category under these land uses (Landon, 1991).The result showed that Mg was resistant to leaching than Na contents in the soil.The mean value of Mg and Na in the soil was similar with a study reported by Yitbarek et al. (2013) which also showed high Mg and low for Na under these land uses.In contrary, the same author had reported the land uses did not affect the contents of Mg and Na in the soil.Findings made by Asrat et al. (2014) on the other hand indicated similar results with Na content under CL use systems.
Av. P in the site showed the highest for GLs as compared to FL and CLs by 66% each (Table 6).No significant variation was observed in average value of Av.P within land use systems under CL and FLs.Land use systems had significant impacts on SOC and TN which showed trends of GL <CL < FLs.Within land use systems, no significant variations were observed between GL and FL systems in SOC; and the same trend was also seen between FL and CLs.
The Av. P in the site showed medium under FL and CL uses; and high under GL use in the site (Landon, 1991).Low amount of Av.P under FL and CL relative to GL might be due to high P fixation in the site.The mean value of Av.P under GL showed comparable results made by Yitbarek et al. (2013) and Haile et al. (2014).The result also showed similar findings with what was reported by Asrat et al. (2014) and Tilahun (2007) under CLs.Again, the mean value of Av.P illustrated similar results with a study reported by Chimdi et al. (2012) under FL use systems.
SOC under both land uses were rated as very low (Landon, 1991).These might be due to inherent property of the soil, OM removal in terms of erosion, crop uptake and crop residue under CLs.FLs especially C. lusistanica plantation was lower in SOC than other adjacent species of natural FLs (Limenih, 2004).Overgrazing might also affect OM under GL uses in the site.The present study goes well with findings reported by Haile et al. (2014) and Tilahun (2007) under both land use systems.Yitabarek et al. ( 2013) also showed similar results with the mean value of SOC under GL and CL uses (Table 6).The mean values of TN in the site were low under CL and FL uses; and very low GL use systems (Landon 1991).The reason might be due to excessive erosion, leaching, removal of OM in terms of crop residue, crop uptake of N and other processes in the site under CLs; and leaching and erosion under FL and GLs.Furthermore, this might be due to low decomposition of OM under FL and GLs which in turn stop N in the soil.These results were similar with findings gotten in the study of Yitbarek et al. (2013) and Chimdi et al. (2012) under FL and GL uses.
The C: N ratio of the soil was the highest for FLs (7.44) followed by GLs (7.11) and CLs (3.80) (Table 6).C: N ration of the soil in the site was lower.The reason might be decomposition is fast under CLs due to intensive tillage and removal of organic matter from agroecosystem by crop residue and animal manure for energy and livestock feeds.FL and GLs did not show impact on soil CN ratio in the site.However, there were clear significant variation between FL and CLs; and GL and CLs.The mean value of C: N ratios were too low under CL uses, consequently causing quick decomposition of OM.This might be due to excessive tillage that plants need N from soil than under FL and GL use systems.The mean value of C: N ratios was similar with the study conducted by Tilahun (2007) under FL and GL use systems.However, the trend showed similar results with studies reported by Chimdi et al. (2012) and Yitbarek et al. (2012) under CLs but the value was lower than the result gotten.

Conclusions
It is primarily the properties of surface soils that would indicate the effect of land use change of the study sites.The properties of lower soil horizons are not going to be changed over a short term cultivation practice; it is more of long term pedogenetic process than any anthropogenic factor.

Doko Yoyira site
Available potassium under forest lands and grazing lands were rated as medium, whereas sodium content under these lands uses were deficient in the soil.The result of available potassium in the soil was low under forest lands and grazing lands but medium available potassium under cultivated land use systems.Soil organic carbon both under forest and cultivated lands were very low.Soil total nitrogen in the site was very low in total nitrogen under cultivated lands; and low total nitrogen under forest and grazing lands.

Aiezo Tula site
Available potassium in the soil was rated high under forest land uses.On the other hand, mean value of available potassium was low under cultivated land uses.The value of sodium content in the soil was low under both land uses.The average value of available potassium in the soil was rated as high under forest lands, but low under grazing land use systems.The mean value of calcium content in the soil was rated as high under forest land and medium under both cultivated and grazing lands.The mean value magnesium content in the soil was high under both land use systems.The rate of soil organic carbon was classified as medium under forest land uses and very low under cultivated and grazing land use systems.The mean value of total nitrogen was rated as very low under cultivated lands, low under grazing lands.On the other hand, mean value of electrical conductivity was rated as very low under both land use systems.

Gendona Gembela site
The mean value of available potassium was demonstrated as low under forest lands, and medium under cultivated and grazing land uses.Content of calcium in the soil was rated as high under grazing lands and medium for both forest and cultivate land uses.Under both land use systems, content of magnesium in the soil was rated as high, whereas sodium content in the soil was classified into low category under these land uses.
The available potassium in the site had showed medium under forest and cultivated land uses; and high under grazing land uses.Low amount of available potassium under forest and cultivated were observed to be relative to grazing lands.The soil organic carbon under both land uses were rated as very low.The mean values of total nitrogen in the site were low under cultivated and forest land uses; and very low under grazing land use systems.Similar results in soil properties indicated that soil in the sites made up the same parent materials, and land uses had the same exposure of disturbances.
The low rates of soil properties in the sites have implications for soil degradation and serious impacts on soil production and productivity in the sites.The results also confirmed that there will be need to develop proper land use policy and sustainable soil management and cropping practices to combat ongoing soil degradation, and also improve soil fertility in the area.It is clear from the results that forest and grazing lands are relatively appropriate land use systems for improving soil properties as reflected by higher contents of sodium, organic carbon, and total nitrogen compared to cultivated lands.
To reverse the situations and to enhance sustainable agricultural production and land management there is an urgent need of appropriate land use policy and land use planning.Therefore, the following agronomic measures are recommended: minimizing frequent plowing, incorporation of crop residues, use of integrated soil nutrients management such as use of organic and inorganic fertilizers, planting legume as rotation crops and incorporation of nitrogen fixings fodder species with herbaceous species.In addition, intensifying widely adapted agroforestry systems such as legume tree species based around cultivated lands which could be an option for improving soil nutrient and carbon storage.Thus, long term effects of exotic tree species on soil degradation, soil test based for each crop responses and effect of erosion hazards on soil and moisture losses should be investigated in the future.

Figure 1 .
Figure 1.Map of the study area.
CEC=Cation exchange capacity, Av.K= Available potassium, OC= Organic carbon, TN=Total Nitrogen, C:N= Carbon to Nitrogen ratio.In each line, different letters show significant differences according to least significant differences test (LSDs) at P<0.05.
significant differences according to least significant differences test (LSDs) at P<0.05.

Table 1 .
Mean values for selected soil physical properties at three sites on surface soil (at 0-20cm) by land uses.

Table 2 .
Mean values of selected soil chemical properties of surface soil (0-20cm soil depth) by land uses.

Table 3 .
Mean values of selected physical properties of soil profiles (0-200cm) of three sites by land uses.
Zewdie (2008)ely.The mean value of Av.K showed similar results with findings gotten byLimenih  (2004)which was lower Av.K under mono E. species than CL but increasing in Av.K under mono C. lusistanica than CL.Findings made byZewdie (2008)showed higher Av.K in contrast to the present study.
which could be affected by medium contribution of litter and collected for firewood from mixed E. globules and Cupressus lusistanica plantations.The Av. K showed significantly lower under FL and GL than CL by 85.33 and 84.

Table 5 .
Some soil chemical properties of Aiezo Tula sampled from soil profiles (0-200cm) across land uses.

Table 6 .
Some soil physical properties of Gendona Gembela sampled from soil profiles (in pits) across land uses.