Impacts of Stone Bund on Soil Quality in Masha-Deniba Micro-water Shed Loma woreda Dawuro Zone of Southern Ethiopia

Background: - Land degradation is one of the major challenges in agricultural production Ethiopia. To combat the problem different Soil and Water Conservation (SWC) measures were introduced. Methods: - This research was conducted in the Masha Deniba micro-watershed, Dawuro Zone, Southern Ethiopia aimed to assess impact of stone bund conservation on soil properties. This study compared the effects of stone bund age along landscape positions. Surface soil sample from 17 farms were collected and analyzed for soil bulk density (BD), organic matter (OM), total nitrogen (TN), pH and cation exchange capacity (CEC) of soil. Result:- Results showed that farms treated with stone bunds showed improvement in soil chemical properties. For most parameters, the peak was obtained from stone bunds having 10 years age. The non- conserved plots had the lowest soil nutrients contents. Lower topographic position had shown higher nutrients contents than farms in upper topographic position. Overall, OC, TN, S and B contents were low in the watershed. Conclusion: - From the finding we can conclude that stone bunds improved soil nutrient when compared to non-treated farm with the respect of age and landscape position. But constructing physical structures alone does not restore the soil fertility to the level that the crop is demanding. Thus, integration of physical conservation with agronomic and biological measures is highly recommended.


Introduction
Soil degradation can be described as deterioration of the physical, chemical and biological or economic properties of soil (Maitima and Olson, 2001). It is a principal environmental problem in Ethiopia which is manifested mainly in the form of soil erosion, soil fertility loss, and crop yield reduction. The excessive dependence of the Ethiopian rural population on natural resources, particularly land, as a means of livelihood is an underlying cause for land and other natural resources degradation (EPA, 1998). Soil degradation is caused and aggravated by erratic and erosive rain fall, topographical setup and inappropriate land use practices ( Generally, water erosion is prominent in highlands of Ethiopia where erratic rainfall generate erosive runoff (Hurni, 1993). Various studies provided empirical evidence of the severity of the problem. For example, the Ethiopian highland reclamation study (EHRS) estimated 1.9 billion tons annual topsoil loss from the highlands due to water erosion, which is equivalent to 8 mm soil depth or 130 t ha − 1 annual losses (FAO, 1986). Hurni (1993) also reported as much as 300 t ha-1 annual soil loss from croplands with average rates of 42 t ha − 1 . The extent of soil loss due to erosion in the Ethiopian highland is high varying between 42 t ha − 1 y − 1 and 175.5 t ha − 1 y − 1 (Admasu et al., 2017).
The impact of soil erosion is complex leading to reduction in soil depth and moisture storage capacity together with soil-nutrient losses, and ultimately results in reduced agricultural production and productivity (Vancampenhout et al., 2006;Tesfaye and Fanuel, 2019). Soil erosion is a threat not only to agriculture but also to the economy, as the country´s economy depends on agriculture.
Soil conservation is the only known way to protect the productivity of the land (Panda, 2007).
Different SWC Measures are in place to mitigate land degradation problems. Their performance considerably varies based on type of structure, age of structure, land scape position (Tesfaye and Fanuel, 2019). Space occupied by soil and water conservation (SWC)structures, impediment to traditional farming activity, water logging problems, weed and rodent problems, huge maintenance requirement, are some of the reasons that cause farmers refrain from SWC works (Mitiku.et al., 2006 (Fig. 1).

Agro-ecology and Soils
Loma woreda has endowed with enormous and diversified land features that different elevation inturn outfits the variability in rainfall and temperature. The altitude the study woreda ranges from The agro ecology according to traditional classification system includes Kolla (i.e., low land), Woyina Dega (i.e., mid highland) and Dega (i.e., high land). About 41%of the zonal land is lies under WeynaDega ecological zones, Kolla covers about 38% and Dega agro-ecological zone constitutes 21% of the total agro-ecological zones. Those three agro-ecological zones are suitable for agricultural production and human settlement.

Farming System
The means of livelihood is based on mixed crop-livestock agriculture where it is dominantly rainfed and subsistence. The major crops under rain fed condition include: maize (Zea mays), tef

Socio-Economic Characteristics
The demographic and socio-economic description highlights based on 17 respondent households.
Gender result indicated that about 94.1%) (n = 16) were headed by male and 1(5.9%) households were headed by female out of which 47% (n = 8) of the households have no formal education and 53% (n = 9) of respondents attended elementary school. As far as the marital status of the heads of household is concerned, 16 (94.1%) married (still living together and 1(5.9%) of the household heads were widowed in relation to this the family size of the respondents showed that 23.5% had 5-7 family, Thus a total of 17 farm lands were identified for soil sample collection in collaboration with woreda experts and site extension worker. In addition, slope, socio-economic characteristics and other relevant information from each farmland was recorded using data collection sheet. Each farm land was also geo-referenced.

Data collected
Disturbed and undisturbed soil sample at a depth of 0-20 cm were taken using augur and core sampler, respectively. About 10 sub-samples from each farm were taken to form one kg composite sample. The sampling under stone bunds includes the area between the two successive structures whereas for non-conserved plots, the sampling refers to the area under cultivation which is found between successive farm boundaries. After soil processing (drying, grinding and sieving), soil physicochemical properties like texture, pH, soil organic carbon (OC), and macro and micronutrient contents and cation exchange capacity (CEC) were analyzed.

Data Analysis
The data was evaluated using descriptive statistics such as mean, standard deviation, minimum, maximum and median. To complement descriptive statistics, Pearson correlation, and regression analysis were performed. Variation in soil properties was also determined using the coefficient of variation (CV) and rated as low (< 20%), moderate (20-50%) and highly variable (> 50%) according to Aweto (1982) cited in Amuyou et al. (2013). For the management purposes, interpretation was given using proper ratings. The data were subjected to general linear model procedure using the SPSS and  Table 1 ). The mean was 1.34 gcm − 3 . Soil BD declined with age of stone bund (Fig. 2). This could be attributed to the effects of reduced soil loss through erosion; and addition of organic matter from plants. Similar results were reported by Tesfaye and Fanuel  Soil pH among age of stone bund varied between 7.05 (3 years) and 7.27 (10 years). The result revealed an increment in soil pH at 10 and 12 Years when compared to untreated farms (Fig. 2).
These might be associated to the decrease of the loss of soil organic matter and exchangeable bases through soil erosion and runoff; and thereby increase soil pH. This is also explained with positive and significant relationship with OC (r = 0.71), Ca (r = 0.67), Mg (r = 0.78) and K (r = 0.63) (Appendix 1).
Soil organic carbon (OC) of farm lands with age of stone bunds showed low variability. The mean of OC (1.99%) was between 1.49% and 2.39% from untreated and stone bund at 10 years (Table 1). It is noted that soil bunds in general, and with increasing age of bunds improved the soil OC of farms (Fig. 2). The mean total N (TN) (0.17) varied from 0.11 to 0.20% obtained from untreated and 10 years stone bund. The result almost followed the trends of soil OC (Fig. 4.9). This signifies that Available P was found highly variable (CV > 50%) among age of stone bunds that varies from 27.7 to 56.9 mg/kg (Table 1) from 3 years and10 years', respectively (Fig. 2). The high variability in available P content may reflect differences within age of stone bunds and soil management. Higher amount of available P from integrated soil bund for 5 years was reported by Tesfaye and Fanuel (2019). The authors explained that reducing soil erosion and runoff, and improved amount of soil OC might result an increased available P on integrated and 5 year age stone bund. Pearon correlation matrix also indicated the positive and significant relationship of available P with OC (r = 0.50), pH (r = 0.55) (Appendix 1). The sulfur content (mgkg − 1 ) ranges from 6.79 (3 years age) to 13.69 (10 years age) with moderate variability (CV = 20-50%). Available S has shown positive and significant relationship with OC (r = 0.53) and pH (r = 0.55) (Appendix 1). The restoration of soil OC and reduced rate of soil erosion and runoff could result an increased available S stone bunds.
Exchangeable cat-ions among age of stone bunds showed moderate variability (CV = 20-50%) ( Table 1). Exchangeable calcium was dominant in the exchangeable site followed by Mg 2+ , K + and Na + . Overall stone bunds showed higher amount of exchangeable cat-ions, and the amount was also increasing with age of stone bund (Fig. 2). This might be attributed with improvements in pH, soil OC and CEC of the soil. Pearson correlation matrix also showed the significant and positive relation exchangeable bases with OC, TN and CEC (Appendix 1). The mean soil micronutrient contents were in the order Mn > Fe > Zn > Mo > Cu > B, and their variability was low (Fe, and Mn), moderate (Cu, Zn, Mo) and high (B) ( Table 1)

Landscape Position and their Effects on Soil Properties
The effect of landscape position averaged over stone bund is summarized in Table 2 Fig. 3). The result regarding available P showed maximum value at middle > lower > upper position. However, Fe was found to have increasing content towards upper positions Table 2; Fig. 3). In

Conclusions And Recommendation
From this study, we can conclude that stone bunds improved soil nutrient when compared to non-

Supplementary Files
This is a list of supplementary files associated with this preprint. Click to download. Appendix.docx