Soil Physicochemical and Macrobiota Diversity Dynamics Under Enclosed Areas of Central Rift Valley of Ethiopia

Background Area enclosures have been implemented for many decades to restore degraded areas. The objective of this study was to evaluate its contribution to the enhancement of soil physicochemical and macrobiata diversity. Results Among the soil physicochemical parameters, the overall mean BD (0.002*), soil-MC (0.000*), % sand (0.011*), % clay (0.038*), pH (p = 0.022*), SOM (p = 0.005*), and Exch. Ca (p = 0.000*), and exch. K (p = 0.000*) exhibited a signicant mean difference across the different land-use while % silt, EC, ava. K, ava. P, TN, CEC, and exch. Mg was insignicant at α-0.05. Although the whole study area was dominated by sandy, the result of ANOVA indicated that there was a signicant mean difference in %sand (p = 0.011*) fraction across the land uses. The SOM also varied signicantly and it is very high in the CA1, followed by CA2, PA, and OA, respectively. Though the result of Tukey's HSDa and homogeneity test showed that there is no statistically signicant mean difference in the amount of available soil nutrients across the study sites, there was a slight variation in their magnitude, and PA was characterized by having high ava. P (9.70 ± 3.261a) and TN (0.28 ± 0.064a) while ava. K is very low (1062.29 ± 110.018a) compared to other land uses. In terms of the soil macrofauna, the CA1 had higher species diversity (1.90), abundance (32.69%), and richness (30.95%), and the species were evenly distributed. Followed by CA1, PA has a good species diversity (1.30), richness (26.19%), and abundance (24.16%), although the soil macrofauna was less evenly distributed compared to other land uses.


Background
Globally, over the last two to four decades, more than half of the earth's land surface has been affected by anthropogenic activities, which was associated with increasing population number, land use and land cover change, expansion of agriculture, and other development activities (Ward et al., 2014). Soil plays signi cant multitude roles (regulating, provisioning, cultural, and supporting services) to humans and the environment (Schwilch et al., 2016). Nonetheless, interference with the increasing world population for pursuing different socio-economic bene ts contributed to extensive land degradation that disturbed the entire earth system and its overall services to society over century (Brevik et al., 2015;Khaledian et al., 2017).
Similarly, in Sub-Saharan Africa, land and other environmental resources degradation is becoming a serious challenge (Lemma et al., 2015) and major threatening factor to development activities (Erkossa et al.,2015). Ethiopia is also one of the developing countries and its major portion of the communities (83%) depends on agriculture, which has facing recurrent drought since the 1970's (Mohammed et al., 2018) and land degradation. This poses a potential impact on the physicochemical quality of soil (Zhang et al., 2015;Fernandez et al., 2014), soil productivity (Wu et al., 2007), and socio-economic impacts like food insecurity, price hick of market commodities, and social instability (Abeje et al., 2019;Mekonnen, et al., 2019). On top of these, several studies concluded that land degradation was also leading to the current global headache which associated with global warming. All these complicated and pressing challenges were either directly or indirectly related to land degradation, and drew the attention of the national government and the continent to desk discussions on the rehabilitation of degraded lands and combating deserti cation using different techniques. Among these, area enclosures, which have been practiced particularly around churches and religious areas for centuries, was reconsidered as the most preferred and affordable system that is widely implemented in most regions of the country, particularly in the study area. However, their contributions to the improvement of soil physicochemical and biological diversity were not exhaustively investigated, which was very di cult to provide information for the communities around the study area so that they will ll the sense of ownership and strengthen their protection and management of closed areas. Accordingly, this particular study was initiated with the objective of investigating the contribution of enclosed area for soil organic carbon and biota diversity improvement.

Description of the study area
Arsi-Negele district is located in the West Arsi zone of the Oromia Region State about 225 km south of the capital Addis Ababa. Geographically, it is situated in the Ethiopian central rift valley system of 7 0 09'-7 0 41' N and 38 0 25'-38 0 54' E. It is bordered in the south by Shashamene district, in the southwest by Bulbula woreda, which separates it from Seraro, on the west of the Southern Nations, Nationalities and Peoples Region, on the north by Adami Tullu and Jido Kombolcha with which it shares the shores of lakes Abijatta and Langano, and on the east by the Arsi Zone (ORS, 2004). The area has an altitude that ranges from 1500-2300m above sea level (ICRA, 2002), and mean annual temperature varies from 10-25 o c while annual rainfall varies between 500-1000 mm (ORS, 2004).
The vegetation of the area is predominantly woody acacia, while the soil types are andosols and nitosols.
Abijata, Shalla and Langano are large water bodies that covers most part of the study area (ORS, 2004).The total population of Woreda is estimated to be 260,129, of which 80.2% is rural, with an average density of 105.4 persons per km2 (CSA, 2007). Rain-fed agriculture, mainly cereal cropping, and livestock raring, are the major sources of food and income for maintaining livelihoods. If area encounter agricultural failure, the community depends on the production and selling of charcoal (Biazen, 2014), and this has its own contribution for natural forest degradation.

Data Collection
The soil samples were collected from quadrats that had been developed following a transect line. Accordingly, the soil samples were collected from different depths of 0-15, 15-30, and 30-45cm and immediately placed in a polythen bag and transported to Wondo Genet College of Forestry for preparation and analysis. As for soil sampling, collection of soil biotas were held following the transect line developed for soil sampling but different quadrats were developed, and collection was conducted by digging the land up to a depth of 0-20cm. This is because most soil biota colonize the top pro le of the soil due to the high availability of nutrients.
Accordingly, organic carbon stock inventory in mineral or organic soil was determined after measuring the depth, bulk density (calculated using core sampling method in gm/cm 3 ), and the concentrations of organic carbon within the sample (Pearson et al., 2005). A 100 g of composite subsamples was taken at each corner and at the center for the determination of soil organic carbon using soil auger, whereas the core sample was used for bulk density determination. In other words, the carbon concentration in the soil was determined by following Walkley-Black (1934) method and core sampling method (using soil cores of 5 cm in diameter and 10 cm length) for bulk density. Soil samples was oven dried for 24 hours at constant temperature of 105 o C until constant weight was obtained to determine the soil bulk density (Eq. 1). The total of the carbon stock density of soil organic carbon was estimated using the Pearson et al. ( contrast, the nding of Abdelkadir and Yimer (2011) stated that bulk density does not vary under different land uses and does not show a signi cant mean difference.
From the soil particle size point of view, the overall percentage of sand (p = 0.011*) and clay (p = 0.038*) shows a signi cant difference across the different land uses at 0.05 level of signi cance respectively (Table 1). In view of this, the whole study area is dominated by sandy fractions followed by silt. However, comparatively there is a great difference in the mean percentage of soil minerals among the land uses.
The soil of the protected area was dominated by sand (63.333 ± 5.993), followed by silt (  In other words, the protected area, closed area one, and two have comparable mean of bulk density, which is the result of relatively low disturbance by livestock and human activity. The soil moisture content is another physical parameter under investigation, which varies and exhibits signi cant mean difference (p = 0.000*) across the land uses. Accordingly, open area has lower moisture (7.770 ± 2.127 b ) followed by protected area, closed area two, and one, respectively. This is probably due to low soil organic matter content, lower vegetation cover, and dominance of sandy soil, which is consistent with the ndings of Abdelkadir and Yimer (2011).
The overall result of correlation analysis (indicated in Table 2        The result of ANOVA analysis also shows that the mean percentage fraction of clay across the area of investigation is signi cantly different (p = 0.038*). However, the silt fraction across land use is not signi cantly different (0.053), although numerically they differ (Table 2). Closed area two recorded the highest clay fraction followed by closed area one, open, and protected area, respectively.

Soil chemical properties
Among the selected parameters for analysis of soil chemical dynamics, pH (p = 0.022*), soil organic matter (p = 0.005*), and exchangeable calcium (p = 0.000*), and potassium (p = 0.000*) showed signi cant mean differences across the different land uses of the study area, while electric conductivity, available potassium, available phosphorus, total nitrogen, cation exchange capacity, and exchangeable magnesium were insigni cant ( Table 3). The mean pH value of the open area (8.04 ± 0.034 b ) was signi cantly very higher than that of the enclosed area two (7.94 ± 0.058 ab ), closed area one (7.79 ± 0.059 ab ), and protected area (7.75 ± 0.100 a ). The higher mean value of pH in open area might be related to the relatively higher leaching of nutrients and lower soil organic matter content, which is in line with the ndings of Umer and Sinore (2019).
The mean value of soil organic matter is signi cantly varied across the study area, and it was very high in the closed area one followed by the closed area two, although Tukey's homogeneity test shows there is no mean difference between the two areas. This is the result of several factors, such as vegetation (Yimer, 2007;Finzi et al., 1998), and management (Yang and Wander, 1999). The ndings of this research are also complementary to the aforementioned studies. According to the study of Buschiazzo et al. (2004), soil organic matter highly depends on clay and silt content when vegetation is dense and uniform, and the coverage is sparse and heterogeneous. The protected area also has higher soil organic matter than the open area. The reason for this variation may be the result of differences in vegetation diversity and composition, and the intensity of disturbance they face from the external environment, mainly livestock and charcoal burning activity carried out by the local community.
The result of multiple comparisons using Tukey's HSD a and homogeneity test showed that there was no statistically signi cant mean difference in available soil nutrients across the four study sites. However, there is a slight variation in terms of available soil nutrients in the area. Accordingly, the protected area was characterized by having high available phosphorus (9.70 ± 3.261 a ) and total nitrogen (0.28 ± 0.064 a ), while available potassium was very low (1062.29 ± 110.018 a) compared to other land uses. Followed by protected area, the closed area revealed a high concentration of phosphorus (5.88 ± 1.374 a ), potassium (2806.46 ± 1478.592 a ), and total nitrogen (0.27 ± 0.091 a ). closed area one, and two). The results of the diversity index showed that the closed area one have a higher diversity of soil organisms compared to other land uses, as indicated in Table 4 below. On top of this, the abundance (32.69%) and species richness (30.95%) were also higher in the closed area one followed by closed area two, which have species richness and abundance of 26.19%, and 24.16%, respectively. These were probably the result of the difference in age of establishment of closed area (i.e., 15 and 12 years for closed area one and two, respectively), its management, and low carbon to nitrogen ratio recoded in the area. Furthermore, ooding of their burrows by excessive rainfall during the seasons of data collection. The distribution pattern of soil organisms was also more even (0.74) in the closed area one (Table 4), followed by closed area two and protected areas. The lowest diversity and species richness of soil organisms was documented in closed area two (0.89) and open area (1.14), which had more species richness and abundance compared to closed area two.
The analysis of the biomass of soil organisms was also performed across the different land uses of the study area. Accordingly, the highest record of biomass per meter square (11.4) of soil organisms was obtained in Open followed by the protected area (6.18).Even though the mean difference of biomass across the land uses was observable from Table 7 below, it was not statistically signi cant at alpha of 0.05 and 0.01. A possible reason for the higher biomass of soil organisms in protected area than others was the availability of high total nitrogen, low pH (7.75), and low carbon to nitrogen ratio (5.04) relative to the other land uses. Where: PA-protected area CA1 -Closed area one CA2 -Closed area two OA -Open area Where: PA-protected area CA1 -Closed area one CA2 -Closed area two OA -Open area

Conclusion And Recommendations
Soil, which is a precious natural resource that provides a multitude of bene ts to socio-economic development and other biological services, has been affected for many decades by anthropogenic activity, and its quality and productivity have deteriorated. On the basis of the ndings, although there are slight differences in the gures of the result for parameters that are associated with differences in age of establishment, management practice, and extent of disturbance, the enclosed area contributed to the improvement of soil physicochemical and biological components. Hence, expanding the enclosure area through consultation with the concerned bodies of the study area and proper follow-up mechanisms has to be considered in order to maintain environmental resource management. The mean soil organic carbon across different land uses under investigation in the study area