Wudpecker Journal of Agricultural Research Vol. 4(1), pp. 006 - 013, January 2015 ISSN 2315-7259 2015 Wudpecker Journals Effects of Hypericum revolutum (Vahl) tree on major soil nutrients and selected soil Physico-chemical properties in Goba District, Oromia, Ethiopia Gonfa Kewessa1*, Lemma Tiki2 and Abiot Molla1 1 Department of Forestry, School of Biodiversity and Natural Resources, Madawalabu University, Bale Robe, Ethiopia. 2 Lemma Tiki, Department of Natural Resource Management, School of Biodiversity and Natural Resources, Madawalabu University, Bale Robe, Ethiopia. *Corresponding Author E-mail: gonfa.kewessa@gmail.com, Tel: +251 913 24 05 74 Accepted 19 January 2015 The study was initiated to quantify the effect of Hypericum revolutum on major soil nutrients and soil properties were traditionally retained on farmlands at Goba District of Oromia Region, Ethiopia. Sampling was done in Randomized Complete Block with two factors: 1) distance from tree trunk (at 0.5m under the canopy, at 2m at edge of the canopy and at 10m in the open area), and 2) soil depth (surface soil; 0 – 15cm and subsoil; 16– 30cm). Bulk density was not significant in distance wise, but it showed significant difference along soil depth. Soil texture showed significant for silt and sand fractions while clay fractions showed no significant as distance increases from tree base to open area. Available Phosphorus and soil organic carbon (SOC) were significantly higher under the canopy than open field. Available Phosphorus was not significant (P=0.66) along the soil depth while SOC was significant (P=0.0001). Available Potassium showed not significant (P=0.17) as distance moves from under tree to open area while it was significant (P=0.04) along the soil depth. Total Nitrogen was found to be significant both distance and depth wise. Inclusion of Hypericum tree on farmlands has a potential to improve organic sources of nutrients. Key words: Parkland agroforestry, soil nutrients improvement, tree based land use systems. INTRODUCTION The World Resources Institute estimates the global human population at 8.5 billion in 2025 and by 2050 the population is expected to hit 10 billion (Mackenzie, 1994). Considering high population growth rates, increasing poverty levels and scarcity of land, the need for technologies that would boost food production including crops and animals, forest and wood products as well as sustaining the use of land cannot be over emphasized (Young, 1987). International concern is to find alternative farming systems that are ecologically and economically sustainable as well as culturally acceptable to farmers. Agroforestry systems are known to bring about changes in edaphic, micro-climatic, floral, faunal and other components of the eco-system through biorecycling of mineral elements, environmental modifications (including thermal and moisture regime) and changes in floral and faunal composition (Shukla, 2009; Manjur et al., 2014). Trees can improve the nutrient balance of soil by reducing unproductive nutrient losses from erosion and leaching and by increasing nutrient inputs through nitrogen fixation and increased biological activities by providing biomass and suitable microclimate (Clement and Olusegun, 2010). A major reason for practicing agroforestry is for domestication of soilimproving trees for enhancing soil productivity through a combination of selected trees and food crops on the same farm field (Kassa et al., 2010). The influence of trees in soil physical properties is very important in augmenting the overall capacity of land productivity. The removal of the vegetative cover increases the bulk density of the soil due to reduction in porosity and infiltration rates (Nair, 1984). This ultimately will dwindle land productivity. Declining land productivity due to soil degradation is a serious problem affecting most developing countries. This is particularly true for the east African highlands including Ethiopia where soil degradation is a common feature of the farming system, necessitating the need for external inputs (Yadessa et al., 1998). This is particularly true also for the highlands of Bale Zone Goba District (study area) 007 Wudpecker J. Agric. Res. where there is high loss of soil through erosion and hence decline in yield production and productivity of the land. Intensive agriculture needs high value inputs and the deteriorating economic situation of most farmers in developing countries demands the need to renew awareness about the age-long productive and protective values of multipurpose trees. Land development through the use of indigenous trees and other locally available resources is relatively inexpensive, and requires no foreign currency (Young, 1989). Despite all the above facts, however, the relative emphasis on artificial fertilizer as a means of soil fertility improvement has led to comparative neglect of the potential of alternative land uses like agroforestry for soil fertility improvement. The local people of Goba District (the study area) retain Hypericum revolutum (H. revolutum) tree on their farm lands. However, there was no research that has been conducted specifically to ascertain the contribution of H. revolutum tree on soil physico-chemical properties regardless of the use of Hypericum by the local communities within the crop field. During the reconnaissance survey to the study area, local farmers those managing Hypericum tree in their cropland argued that it has many uses. Hypericum is important in soil fertility maintenance because it is evergreen and its leaves and flowers decompose rapidly. Besides, it provides firewood, timber (local construction), medicine (powdered dry leaves and stems, oily extracts), bee forage, soil conservation and other benefits that are vital to the rural communities (Bekele, 2007). It is a shrub or tree which can reach 10 m, usually smaller (Bekele, 2007). It was noted in the study area, it can grow up to 12 m. This study was initiated to quantify the effects of H. revolutum tree to soil properties with scientific evidences as there was no documentation so far on the effects of Hypericum tree to soil properties. MATERIALS AND METHODS The study area Mount Tullu Demtu is the highest point in this District, the Zone and the Oromia Region; other important peaks include Mount Batu. Rivers include the Togona and Shaya. A survey of the land in this District showed that 13% is arable or cultivable, 27.6% pasture, 54.6% forest (or part of the Bale Mountains National Park), and the remaining 4.8% is considered degraded unusable. The altitude of the District ranges from 1500-4377 meter above sea level (m_asl) (BMNP, 2006). Climate Goba District has bimodal rainfall. Annual rainfall ranges between 600-1500 (2000) mm depending on the relief. The average temperature for Goba is 13.1 o C (ETFE, 2007). Soil and vegetation The major soil types found in the Goba District are Chromic and Pellic Vertisols in some parts, Chromic, Orthic and Vertic Luvisols around highlands and plateaus areas (BMNP, 2006). The most dominant tree species found in the area include: Celtis africana, wild Coffee arabica, Cordia africana, Bersama abyssinica, Croton macrostachyus, Apodytes dimidiata, Ekbergia capensis, Ficus sur, Hagenia abyssinica, Juniperus procera, Millettia ferruginea, Afrocarpus falcatus, Prunus africana, Scheffilera abyssinica, Syzygium guineonse, and many others (BMNP, 2006). Agroforestry practice The types of agroforestry practice noticed in the study area were retaining of indigenous trees in the farmlands. Cereal crops like barley and wheat productions were grown commonly under different indigenous trees in the area. Farmers of the study area rarely apply inorganic fertilizers to their farmlands. Land preparation was undertaken manually with oxen plow. Location Goba District is one of the Districts’ found in Bale Zone South East Ethiopia. Geographically, it lies between 39o 37’ 30’’– 40o 12’ 00’’E and 6o 38’ 0’’ – 7o 4’ 0’’ N. It is bordered on the South by Dellomenna and Harena Buluk Districts, on the North by Sinana and Dinsho Districts, on the North West by Adaba and on the Southeast by Berbere District (BMNP, 2006). Topography and land use About 45% of this District is rugged or mountainous; Experimental design and field layout The study was carried out on farmers’ farm land at Rira area in Goba District to compare the soil fertility status under traditionally retained scattered H. revolutum tree against the open farmland outside the canopy cover. The selected soil properties were bulk density, soil texture, soil pH, soil organic carbon, total Nitrogen (N), Available Phosphorus (P), and Available Potassium (K). To collect data on these soil properties, six isolated and nearly identical with diameter at breast height (DBH about 35 40 cm), crown diameter (3 - 4 m) and heights (8 – 12 m) Kewessa et al. were systematically selected for the study to make other soil forming factors nearly constant. The sample was taken from previously barley cultivated field. Two factors were considered as treatments which are distance from the tree base as one factor and depths of the soil from the surface of the soil as the second factor. The first factor had three levels: under canopy, at the edge of tree canopy and at open area at least 10m from the tree trunk (Figure 1). The second factor had two levels: at 0-15cm (which represent surface soil) and 1630cm (which represent subsoil). Generally, the design was 2*3 factorial arrangements of treatments in randomized complete block design replicated six times, that is, under six scattered H. revolutum tree. Totally, there were 2*3*6 (36) sample units for soil sampling. Data collection Soil samples were collected from the six scattered Hypericum tree trunk at three horizontal radial distances and two soil depths from four directions following Yadessa et al. (1998). Soil samples were collected by using core sampler size of 98.125cm2. To collect undisturbed soil sample for bulk density, 30×30cm pit was dug out to control soil disturbance during sample collection. One kilogram (1kg) soil samples was collected by using soil core sampler by adjusting with the required soil depth layers and by carefully cleaning the equipment at each soil sampling distances and depths. Then the soil samples from the same distance and depth were mixed thoroughly to make composite samples for each individual tree. Finally, 1kg of representative soil sample from each composite sample is taken for soil laboratory analysis by reducing the composite in quartering. Soil laboratory analysis To assess the effects of Hypericum tree on soil properties, laboratory analysis was conducted to determine the major soil physico-chemical parameters. Prior to analysis, each composite soil samples were prepared after mixing sub-samples collected from six trees. At same time, before analysis the samples were air dried and then passed through the 2mm sieve to remove unwanted materials from the sample. Laboratory analyses were conducted at Jije Analytical Testing Service Laboratory (JATSL) at Addis Ababa using the following standard methods. Soil texture was determined by Bouyoucos hydrometer method (Gee & Bauder, 1982). Soil pH-H2O 1:2.5 were measured by FAO Potentiometric – Water extract (Rhoades, 1996), and soil organic carbon by Walkley and Black method (Bremner & Mulvaney, 1982). The percent soil organic matter was calculated by multiplying the percent organic carbon by a 008 factor of 1.724, following the standard practice that organic matter is composed of 58% carbon. Total Nitrogen (N) was determined by Kjeldahl method (Bremner & Mulvaney, 1982), and Available Phosphorous was determined using the standard Olsen extraction method (Olsen et al., 1954). Available Potassium was determined using Flame photometry (Jaiswal, 2003). Dry bulk densities were calculated from undisturbed soil sample by dividing oven dry mass at 105oC by the volume of the core sampler (Landon, 1991). Statistical analysis Two way analyses of variances (ANOVA) were performed to assess the total variations that occurred within soil parameters. General linear model procedure of the statistical analysis system (SAS Institute, 1996) was used to assess the interaction effect between distance and depth. Significant differences were declared at P < 0.05. RESULTS AND DISCUSSION Effects of H. revolutum tree on soil physical properties Bulk density (BD) The soil BD increased from 0.97 to 1.01 within distance of the tree from under the canopy (0.5m) and to the open area (10m) (Table 1). However, there was no significant difference (P=0.93) in BD among the three radial distance from the trunk of the tree to the open farm land. But there was significant difference (P=0.02) in BD along the soil depth (Table 1). This decline in bulk density at the surface soil might be due to frequent cultivation and organic matter coverage than at the sub-soil. It is known that incorporation of organic matter in soil improves physical (aggregate stability, bulk density, water retention) and biological properties (nutrients availability, cation exchange capacity, reduction of toxic elements) of soils. On the contrary to the current study, lower bulk densities were observed under isolated Croton macrostachyus (Ashagrie et al., 1999) and Milletia ferruginea (Hailu et al., 2002) trees. Manjur et al. (2014) also reported lower bulk densities under scattered Faidherbia albida and Croton macrostachyus in the Umbulo Wacho watershed, southern Ethiopia. The difference could be due to the distribution of organic matter under the canopy of Hypericum tree with the area outside the canopy zone during land preparation/cultivation using oxen. In addition, this difference might be due to difference in the nature of organic material addition by different tree 009 Wudpecker J. Agric. Res. Figure 1. Systemmatic representation of soil sampling from H. revolutum tree. Source: Adopted from Ashagrie et al. (1999) and Kassa et al. (2010) Silt (%) Sand (%) 0.83 1.14 -0.19 0.15 34.59 38.67 -2.74 -2.66 32.75 28.17 -5.08 -4.83 32.67 33.17 7.84 7.5 aA 1.02± 0.04 a 0.99 ±0.01 aA 1.01±0.06 a 37.33 ±2.68 a 41.33± 2.20 aA 39.33 ±1.76 a 37.83 ±5.00 a 33± 4.41 bB 35.42 ±3.26 a 24.83 ±5.66 a 25.67± 3.80 C 25.25 ±3.25 Overall depth aA 0.91±0.04 a 1.09±0.08 aA 1.00± 0.05 a 36.67± 1.58 a 41 ±2.73 aA 38.83 ±1.64 a 37.5±4.04 a 32.83 ±3.97 AB 35.17 ±2.79 a 25.83±4.72 a 26.17±5.48 BC 26 ±3.45 at 10m (5) aA 0.74± 0.13 bB 1.19±0.06 A 0.97 ±0.10 32.5 ±3.27a a 36.33± 2.94 aA 34.42± 2.18 a 28 ±2.91 a 23.5± 1.26 aA 25.75± 1.66 a 39.5 ±5.72 a 40.17± 4.11 aA 39.83± 3.36 at 2m Mean values at 0.5m depth D/f B/n col. 7 & 5 (%) Soil texture Clay (%) 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall OMCZ (7) BD (g/cm3) Soil (cm) Parameters Table 1. Bulk density and soil texture as affected by distance from H. revolutum tree and soil depth. a 0.89 ±0.05 b 1.09 ± 0.05 0.99±0.04 a 35.5±1.51 a 39.56±1.54 37.53±1.53 a 34.44 ±2.47 a 29.78±2.18 32.11±2.33 a 30.06 ±3.34 a 30.67±2.95 30.37±3.15 *Mean values followed by different small letter (s) within the same column and different capital letter(s) within the same row are significantly different at (p < 0.05). Where: OMCZ = overall mean of canopy zone (at 0.5m, 2m, and 10m), D/f = difference, B/n = between and col. = column. species. Soil texture The textural classification of the soil was predominantly clay, silt followed by sand. The mean clay proportion of the soil under the tree canopy was lower than the open farmland (Table 1). The present study is inconsistent with the results reported in other related study that indicated the clay fraction was higher under the Faidherbia albida canopy and Croton macrostachyus than open area (Manjur et al., 2014). Other studies on Faidherbia albida, Millettia ferruginea and Cordia africana (Kamara and Haque, 1992; Hailu et al., 2002) were also indicated higher clay fraction under the canopy of these species than under open farmland conditions. Similar to the present result, Manjur et al. (2014) reported that the soil sand content was higher under the canopy of Croton macrostachyus and Faidherbia albida tree. Contrary to the present study, Asfaw (2003) reported non-significant difference between Cordia africana, Millettia ferruginea and Eucalyptus camaldulensis tree species in Sidama, Southern Ethiopia. Although the findings of the silt and sand content were found to be Kewessa et al. higher under Hypericum tree, in reality soil texture is mainly dependent on parent materials of the soil. However, this trend could be related to the protection of the soil by the trees from the impact of rain droplets and wind erosion. Effects of H. revolutum on soil chemical properties Soil pH Soil pH was lower at 0 - 15 cm soil depth as compared to the 16-30 cm soil depth. But there was no significant difference (P=0.05) in soil pH across distance from the tree trunk and between the two soils depths. Similar to this finding Gindaba et al. (2005) reported that there was no significant difference in soil pH under the canopy of Cordia africana and Croton macrostachyus compared to the open area. Other study by Manjur et al. (2014) also revealed there was no significant difference (P<0.05) in soil pH under the canopy of Faidherbia albida and Croton macrostachyus compared to open area and at varying soil depths. Contrary to this finding Kahi et al. (2009) reported significant difference (P<0.05) in pH between the soils under and outside the canopies of Faidherbia albida and Croton macrostachyus, with a lower pH under the canopy areas than in the open cultivated. Kamara and Haque (1992) also reported a significant variation in soil pH horizontally under Faidherbia albida tree canopy. In the present study, higher organic matter distribution coupled with sufficient soil moisture may have led to the similarity of pH values. Soil organic carbon and total nitrogen Organic matter (OM) has an important influence on soil physical and chemical characteristics, soil fertility status, plant nutrition and biological activity in the soil (Brady and Weil, 2002). Soil organic carbon (SOC) was determined to estimate the amount of organic matter in the soil. In this study, SOC was significant (P=0.002) under the canopies of the scattered H. revolutum tree and showed a decreasing trend with increasing distance from the base of the tree towards the open field (Table 2). Similarly, SOC was statistically significant (P=0.0001) along the soil depth. The reason for higher organic carbon under Hypericum tree canopy was quite logical as the higher contents of organic matter under the tree canopies were due to the leaf litter fall and decomposition of dead roots from the tree. Total Nitrogen was found to higher under the canopy (at 0.5m) when compared with the open area (at 10m) (Table 2). Similar with this finding, Nigusie (2006) reported that there was gradual and significant decrease in SOC with increasing distance away from the tree trunk in Harerge 010 highlands, Ethiopia. Mekonnen et al. (2009) also reported that the content of OC showed a decreasing pattern with soil depths and with increasing radius from the closest to the midst and distant positions under Hagenia abyssinica, Senecio gigas, Chamaecytisus palmensis and Dombeya torrida trees canopy. SOC content was also found to be significant under the canopy of Faidherbia albida and Croton macrostachyus (Manjur et al., 2014). Likewise, Yadessa et al. (2001), Hailu et al. (2002) and Asfaw and Agren (2007) have also reported a significant decrease in OC and OM away from the tree trunk to the open cultivated land. Regarding soil depth, Gindaba et al. (2005) has reported that the surface SOC under Croton macrostachyus and Cordia africana tree was higher than that of the subsurface soil. Available phosphorus and available potassium Available Phosphorus was significantly affected (P=0.027) as distance increase from canopy zone to open farm land (Table 3). But Available Phosphorus was not significant (P=0.66) along the soil depth. It also showed a decreasing trend with increasing distance from the tree base towards the open cultivated land. Similarly, Nigusie (2006) found higher level of Available Phosphorus under the canopy of the Cordia africana, Faidherbia albida and Croton macrostachyus than the outside of the canopy in the Harergie Highlands. Hailu et al. (2002) also reported higher Available Phosphorus under the canopy of Milletia ferruginea tree than the open land. Moreover, Manjur et al. (2014) also reported that Available Phosphorus was higher under the canopy of Faidherbia albida and Croton macrostachyus tree species than the open cultivated land in the Umbulo Wacho watershed, Southern Ethiopia. Contrary to these findings, Ashagrie et al. (1999) and Yadessa et al. (2001) reported a significant decrease in Available Phosphorus under Croton macrostachyus and Cordia africana as compared to the open cultivated land. This difference in the Available Phosphorus could be due to the association of other wild animals inhabiting the tree species is different because of the nature of the canopies and agro-ecology. As distance moves from the trunk to the open land Available Potassium was no significant different (P=0.17). But it was significantly different (P=0.04) along the soil depth from the surface to the sub-surface (Table 3). The highest values of Available Potassium for the surface soil (2.22mg/kg) was recorded at the distance of 0.5 m, and the value was found to decrease to (0.92mg/kg) at the distance of 10 m away from the canopy of H. revolutum tree (Table 3). In line with this finding, Asfaw and Agren (2007) reported that the potassium concentrations under Cordia africana were significantly higher. Similar result 011 Wudpecker J. Agric. Res. pH (H2O) OC % OM % TN % C/N ratio D/f B/n col. 7 & 5 (%) a 5.36± 0.17 a 5.39 ±0.19 a 5.37 ±0.12 a 5.65 ±0.51 a 4.82± 0.21 cC 5.23 ±0.29 b 9.74±0.89 b 8.31±0.36 bB 9.02±0.51 a 0.55±0.39 a 0.45±0.029 bB 0.5±0.027 a 10.21±0.28 a 10.78±0.49 bB 10.497±0.29 OMCZ (7) a 5.55±0.16 a 5.56±0.15 a 5.55± 0.11 a 7.10±0.26 b 4.86 ±0.25 abAB 5.96 ±0.37 ab 12.16±0.45 c 8.37±0.43 abAB 10.27±0.64 a 0.658±0.011 b 0.48±0.022 abAB 0.569±0.029 a 10.74±0.51 a 10.11±0.16 bB 10.43±0.275 Overall depth at 10m (5) 5.50± 0.16a a 5.52 ±0.13 a 5.51 ±0.10 a 6.30 ±0.18 b 4.92± 0.26 aA 5.61± 0.26 a 10.86±0.30 b 8.47±0.44 aA 9.67±0.44 a 0.75±.063 a 0.49 ±0.011 aA 0.625 ±0.049 a 8.68±0.79 a 9.9±0.35 aA 9.29±0.45 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall at 2m at 0.5m Mean values Soil (cm) Parameters depth Table 2. Soil pH, organic carbon, total nitrogen as affected by distance from H. revolutum tree and soil depth. 5.47 ±0.09a 5.49 ± 0.09a 5.48±0.06 a 6.33 ±0.23 b 4.86±0.13 5.59±0.18 a 10.92±0.40 b 8.38±0.22 9.65±0.31 a 0.65±0.031 b 0.48±0.014 0.564±0.022 a 9.88±0.375 a 10.27±0.217 10.073±0.216 5.53 5.54 0.17 0.15 6.70 4.89 1.05 0.07 11.51 8.42 1.77 0.11 *Mean values followed by different small letter (s) within the same column and different capital letter(s) within the same row are significantly different at (p < 0.05). Where: OMCZ = overall mean of canopy zone (at 0.5m, 2m, and 10m), D/f = difference, B/n = between and col. = column. 17.64 13.51 12.59 8.38 2.09 1.04 1.17 0.47 8.61±3.33 a 7.51 ±3.04 AB 8.06 ±2.16 a 1.96±.088 a 1.05 ±.05 aA 1.51 ±0.50 a 5.05 ±1.23 a 5.13± 1.47 C 5.09 ±0.92 a 0.92 ±0.31 a 0.57± 0.16 aA 0.75 ±0.18 Overall depth a at 10m (5) 26.67 ±17.26a a 19.51± 13.14 A 23.10± 10.4 2.22 ±0.41a b 1.03± 0.27 aA 1.63± 0.29 at 2m Mean values at 0.5m depth D/f B/n col. 7 & 5 (%) Av. K (mg/kg) 0 – 15 15 -30 Overall 0 – 15 15 -30 Overall OMCZ (7) Av. P (mg/kg) Soil (cm) Parameters Table 3. Available Phosphorus and Available Potassium as affected by distance from H. revolutum tree and soil depth. a 13.44 ±5.98 a 10.72±4.52 12.08±3.69 a 1.70 ±0.35 b 0.89± 0.19 1.29±0.21 *Mean values followed by different small letter (s) within the same column and different capital letter(s) within the same row are significantly different at (p < 0.05). Where: OMCZ = overall mean of canopy zone (at 0.5m, 2m, and 10m), D/f = difference, B/n = between and col. = column. CONCLUSION AND RECOMMENDATIONS improves soil fertility in small-holder farms of Goba District Rira area, Southeastern Ethiopia. H. revolutum tree can be used as an economically feasible, environmentally friendly and sustainable alternative to maintain soil fertility to resource poor farmers in similar agro-ecological conditions elsewhere. Hence, the research encourages the following recommendations: The study concluded that there were no significant differences in BD, clay (%), pH (H2O) and Av. K under the tree canopy and outside the canopy area. However, OC, OM, TN and Av. P were significantly higher under the base of the tree (at 0.5 m) while comparing with outside the canopy area (at 10 m). Hence, it could be concluded that the management of H. revolutum tree in farm lands a) Agroforestry systems are found to have positive effects on some soil physical and chemical properties when compared to monocropping systems. Therefore, there is a need expand the practice in resource poor farmers in particular and in different farming systems for soil nutrients improvement, microclimate amelioration and other uses for the society. was also indicated that high values of Available Potassium under Faidherbia albida and Croton macrostachyus than open cultivated land (Manjur et al., 2014). Kewessa et al. b) Moreover, study on soil microbial population associated with Hypericum tree, such as Mycorrhizae and Rhizobial associations and rooting systems and their effect to soil textural effect is needed. ACKNOWLEDGEMENT The authors thank Madawalabu University for providing financial support for the research work. Authors also thank Goba District Agricultural and Rural Development Office and Rira Kebele Administrations for providing the necessary information and facilitating conditions while carrying out this study. Rira Kebele farmers’ were highly acknowledged for their cooperation during soil sample collection from their fields. Jije Analytical Soil Testing laboratory workers were also acknowledged for their cooperation in preparation and soil data analysis. Moreover, authors are grateful to the editorial office of Wudpecker Journal of Agricultural Research for their invaluable comments provided on the manuscript. REFERENCES Asfaw Z (2003). Trees species Diversity, Top soil conditions and Arbuscular Mycorrhizal Association in the Sidama Traditional Agroforestry land use, Southern Ethiopia. Swedish University of Agricultural Sciences. Uppsala, Sweden. Asfaw Z, Agren GI (2007). Farmers’ local knowledge and topsoil properties of agroforestry practices in Sidama, Southern Ethiopia. Agroforest. Syst. 71: 35-48. Ashagrie Y, Mamo T, Olsson M (1999). Changes in Some Soil Chemical Properties under Scattered Croton macrostachyus Trees in the Traditional Agroforestry System in North-Western Ethiopia. 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