Impact of Watershed Interventions on Soil Physicochemical Properties in Kechi Micro-Watersheds of Kechi District, Dawuro Zone, Ethiopia

A watershed refers to any topographically delineated area that can collect water and is drained by river system w ith an outlet. The objective of this study is to evaluate the impact of watershed interventions on soil properties micro-watershed of Kechi distirict, Dawuro zone, SNNPR Ethiopia. In this study the researcher adopted a combination of both quantitative and qualitative methodologies. The necessary information was collected from both from primary and secondary sources. Soil samples were collected using 15-cm depth auger and 294.375 cm3 core sampler at a depth of 0–30 cm. A total of 24 composite and core soil samples from Conserved and Non conserved watershed were collected. Soil samples were collected from upstream, midstream, and downstream part of the watershed to make representative for the whole watershed. Soil sample which was taken from representative area was analyzed by soil laboratory analysis. Watershed interventions have resulted in a statistically significantly higher mean value of total nitrogen, exchangeable Na+ and Mg2+ at p < 0.01, and of soil organic carbon and organic matter at p < 0.05 in the watershed. The clay content, soil reaction, cation exchange capacity, and exchangeable K+ showed non-significant, but higher mean values in conserved plots. Furthermore, the effects of conservation practices on soil properties were found more effective in cultivated land uses as compared to that of grazing land uses. This is because conservation treatments had significant effects on organic carbon, total nitrogen, exchangeable Na+ and Mg2+ in cultivated land uses but only on exchangeable Na+ in grazing land uses. The interaction effect of treatments and land uses did not reach a statistically significant result for any of the soil properties considered in this study. Watershed interventions have important implications for improving soil fertility in the kechi micro watershed. Therefore, proper guidance and follow-up, use of agro-forestry and grass strips, and maintenance are required for the watershed’s sustainability and good soil


INTRODUCTION
Government of Ethiopia have initiated watershed development since 1970's and 1980's respectively and increasingly been managed and developed for poverty alleviation and environmental conservation (Chimdesa, 2016).In Ethiopia 85 percent of the population are directly dependent on the agricultural economy. Watershed resource degradation is a serious problem in the Ethiopian which threatening agricultural development and rural livelihood. Since the economy of the country is agrarian in nature, the decline in agricultural productivity adversely affects the economic growth of the country. However, the productivity of that economy is being seriously eroded by unsustainable land management practices, both in areas of food crops and in grazing lands (FAO, 2016). The Government has been recognized that protection of watersheds cannot be achieved without the improving the livelihood of local people and taking lessons from the past shortcomings and it has been initiated community based watershed management (Habtamu, 2011). At socio-economic level a watershed includes people, their farming system and interactions with their land resources, coping strategies, social, economic and cultural aspects (Adane, 2010). Watershed management is the management of land and other resources on a watershed to achieve well-defined environmental, social, and economic goals. Watershed degradation, in turn, leads to accelerated ecological degeneration, reduced economic opportunities and increased social problems (Berry, 2016).
Most watershed interventions are implemented with the twin objectives of soil and water conservation and enhancing the livelihoods of the rural poor. Different types of treatment activities carried out in a watershed include soil and moisture conservation measures in agricultural lands (contour/ field bunding and summer ploughing), drainage line treatment measures (loose boulder check dam, minor check dam, major check dam, and retaining walls), water resource development/management (percolation pond, farm pond, and drip and sprinkler irrigation), crop demonstration, horticulture plantation and afforestation The aim has been to ensure the availability of drinking water, fuel wood and fodder and raise income and employment for farmers and landless labourers through improvement in agricultural production and productivity (Rao, 2017).
Composite soil samples were air-dried, grinded, and sieved to pass through a 2 mm sieve to make it ready for lab analysis. The soil laboratory analysis was done at Jimma Agricultural research center. Selected soil fertility indicators such as soil texture, soil pH, bulk density, total nitrogen, organic carbon, available phosphorus, exchangeable bases, and caution exchange capacity were analyzed using standard laboratory procedures. For the analysis of total nitrogen and organic carbon content, the soil sample was further sieved by 0.5 mm sieve. The soil bulk density was determined by core sampler method described in Black et al. (1965). The determination of soil particle size proportions were carried out by hydrometer method suggested by Sakar and Haldar (2005). Following this, the determination of soil texture and textural classification ware identified using equilateral triangle suggested by United States Department of Agriculture (USDA) and described by Osman (2013). Soil reaction (soil pH) was determined by a 1:2.5 soil: water ratio using a pH meter as described by Van Reeuwijk (2002). The soil organic carbon (SOC) concentration was determined by using Walkley and Black rapid titration method as described in Sakar and Haldar (2005). Soil organic matter (SOM) was determined by multiplying percent organic carbon by 1.724 (Jones 2001). Total nitrogen (TN) was determined by the modified Kjeldahl methods as modified by Sakar and Haldar (2005). The available phosphorus (av. P) content was determined using Olsen extraction method as described by Van Reeuwijk (2002). The exchangeable bases and CEC were determined by using ammonium acetate method (Sakar and Haldar 2005). Ca2 + and Mg2 + were determined by atomic absorption spectrophotometer; flame photometer method was used for determination of Na+ and K

Statistical analysis
Mean and mean differences were used as a descriptive statistical analysis method. One-way ANOVA was used to test whether there is a significant difference in soil physicochemical properties between conserved and nonconserved plots. Two-way ANOVA was applied to test whether soil properties are affected significantly due to the interaction effect of land uses and SWC treatment. In addition, bivariate correlation analysis was used to show the relationships between soil physicochemical properties.

RESULTS AND DISCUSSION Selected Soil Physical Properties under Different Land Use Types Soil particle size distributions
The textural classes were identified using soil equilateral triangle recommended by USDA and described by Osman (2013). Accordingly, the mean particle size proportion showed that the soil was fine textured in conserved and non-conserved plots. The soil in the study area has been dominated by clay content experiencing a mean value of 67.8% and 60.5% in conserved and non-conserved soil respectively (Table 1), which implies that the mean value of clay content was higher under conserved plots. The mean sand fraction is the lowest proportion of soil particle content in the area. It was also indicated that the mean sand fraction was relatively lower in conserved plots. This might be attributed to the relative effect of SWC on soil erosion, which reduces the removal of top fine soil particles. On the contrary, higher sand content of the soil in non-conserved plots may be resulted due to removal of fine particles via soil erosion. A land that receives a high amount of rainfall and continuously cultivated without any conservation measure could allow free and easy removal of fine particles via rainfall runoff. The silt content of the soil was higher in non-conserved plots against the conserved plots. However, the differences in the mean soil particle size distribution (sand, clay, and silt) among conserved and non-conserved plots were not statistically significant at p < 0.05 (Table 1).

Soil bulk density
The effect of watershed intervention on the mean soil bulk density was found to be minimal and slightly lower values were observed in conserved plots. A relatively higher bulk density in non-conserved plots could be related with washing out of fine organic matter rich soils by erosion and thereby exposed slightly heavier soil particulates. The ANOVA result indicated that the variation in bulk density was not statistically significant following treatment (p < 0.05; Table 2).

The Impact of watershed intervention on soil chemical properties Soil reaction (soil pH)
The acidity level of the watershed in general was rated as medium acidic based on Osman (2013) acidity and alkalinity categories of soil pH. The mean pH of the soil in the study watershed was 5.77 and 5.66 in conserved and non-conserved land respectively ( Table 2). The acidity of the soil could be related with its sub-humid nature of the area and high amount of rainfall. This is true that greater rainfall increases soil acidity and humid areas are more acidic than arid and semi-arid areas (Osman 2013).

Soil organic carbon (SOC) and soil organic matter (SOM)
The analysis of variance result for SOC and SOM showed a statistically significant mean difference following treatments (p < 0.05; Table 3). The mean organic carbon and organic matter content of the soil in conserved plots were higher (SOC = 2.49%, SOM = 4.3%) than non-conserved plots (SOC = 1.66%, SOM = 2.83%). Besides, the mean soil organic carbon (SOC) content was rated low in conserved and very low in non-conserved plots according to the rating standard developed for tropical soils (Landon 2013). It could be explained by soil erosion, continuous cultivation, harvesting crop residues, and animal dung. The use of animal dung for fuel instead of manure may reduce the effectiveness of SWC practices in SOC concentration (Mengistu et al. 2016).

Total nitrogen
The total nitrogen (TN) content of the soil was significantly affected by SWC practices (p p <0.01; Table 3). TN content of the soil in Kechi watershed was rated medium and low in conserved and non-conserved plots respectively (Landon 2013). The mean total nitrogen of the soil was greater in conserved (0.27%) than nonconserved plots (0.138%).  Available phosphorous Available phosphorous of the soil was not significantly affected by conservation measures (p > 0.05). Its mean value was lower in conserved plots (6.96 ppm) as compared to non-conserved plots (7.9 ppm) ( Table 3). The varations in the use of artificial fertilizer (diammonium phosphate) may be the reason for the previaled varations in the soil. As compared to the requirements of crops that have been dominantly practiced in the area, the phosphorous content of the soil was questionable (4.1-8 ppm) and deficient (< 11 ppm) for low demand crops (such as cereals and maize) and high demand crops (such as potatoes, onions) respectively (Landon 2013).

Cation exchange capacity
According to the rating standards of Landon (2013), the cation exchange capacity (CEC) of the soil in kechi micro watershed was rated as high (25-40 cmol(+) kg−1 ) in both conserved and non-conserved micro watershed. The study result revealed that watershed intervention had a positive effect on the CEC content of the soil. The mean difference was higher in Tura (33.6 cmol(+) kg−1 ) than Tuta (31.9 cmol(+) kg−1 ) ( Table 3), but not statistically significant (p > 0.05). This is believed to be caused by the relative effect of conservation measures in the watershed.

The effectiveness of Watershed intervention in different land uses
As shown in Table 4, the analysis of variance result for the mean differences of all soil particle size distributions was not significantly affected by conservation practices in both land uses (p > 0.05). However, mean differences were observed in cultivated and grazing land uses following treatments. The highest sand fraction was recorded from non-conserved cultivated land and lowest in conserved grazing land. The mean clay content of the soil was 65.67% and 62% in v cultivated plots. The mean difference for bulk density was slightly higher in cultivated land, with higher mean values in the non-conserved than in the conserved land (Table 4). It was not the case for grazing land uses, in which conserved plots experience higher mean values than non-conserved plots. The ANOVA result indicated that the variation in bulk density was not statistically significant between the conserved and non-conserved lands for either cultivated or grazing land uses due to watershed intervention (p > 0.05; Table  4). The influence of land use on the effect of conservation measures for the mean difference of soil pH was slight. Higher SOC concentration was observed in grazing land uses than in cultivated land uses. Our analysis result by land use revealed that the mean difference in SOC and SOM was higher and statistically significant (p < 0.05) between conserved and non-conserved cultivated land uses. Higher TN content of the soil was observed in Tura grazing land uses (0.32%) followed by Tura cultivated land uses (0.219%) and non-conserved cultivated lands constitute the lowest (0.105%) ( Table 5). The ANOVA result revealed a significant effect on effectiveness of conservation measures on cultivated plots at p < 0.01. Conversely, conservation measures did not show a statistically significant variation for SOM, SOC, and TN in grazing lands (p < 0.05). The SWC treatments for available phosphorous were not significantly affected by land uses (p > 0.05). Instead, greater concentrations were observed in Tuta (9.755 ppm) than in Tura cultivated land (7.78 ppm) (Table 5). Grazing land uses revealed very small mean difference for available phosphorous following watershed interventions. The use of inorganic 29 fertilizer (diammonium phosphate) to enhance crop production in cultivated land could probably increase av. P concentrations in cultivated plots. The CEC content of the soil in conserved and non-conserved land uses revealed 31.97 cmol(+) kg−1 , 35.3 cmol(+) kg−1 in cultivated land and 29.56 cmol(+) kg−1 , 34.3 cmol(+) kg−1 in grazing land respectively (Table 5). The influence of conservation structures on CEC was not determined by land uses and the mean difference was not statistically significant for both land uses. However, the impact of watershed intervention has been better in cultivated land uses as compared to grazing land uses. The effect of watershed intervention in cultivated and grazing land uses showed a statistically significant difference in exchangeable Na+ for both land uses (p < 0.05) and exchangeable Mg2+ only in cultivated land use (p < 0.01). A two-way between groups analysis of variance was conducted to explore the impact of SWC treatment and land use types on soil fertility variation. The result showed a statistically significant main effect for SWC treatment on SOC, SOM at p < 0.05, and TN, Na+ , and Mg2+ at p < 0.01. The main effect for land uses was statistically significant only for SOC, SOM, and bulk density at p < 0.05. However, the interaction effect of watershed intervention and land uses did not show a statistically significant mean difference for any of the selected soil fertility indicators (p < 0.05; Table 6).    (Table 7). It also showed significantly negative relationship with BD (−0.426*). The correlation matrix further revealed a positive very strong significant relationship (0.959**) between TN and SOM and strong positive significant correlation (0.7**, 0.783**, 0.734**) with CEC, exchangeable Na+ , and Mg2+ content. Similarly, bulk density showed strong negative significant relationship (−0.702**, −0.756**, −0.747**) with OM, CEC, and exchangeable Ca2+ content of the soil respectively. However, available phosphorous showed no regular trends and weakly varied with other soil physicochemical properties in kechi micro watersheds (Table 7). Av. P available phosphorous, BD bulk density, CEC cation exchange capacity, SOC soil organic carbon, SOM soil organic matter; **,* the correlation is significant at p < 0.01 and p < 0.05 respectively (two-tailed); TN total nitrogen

Discussion The impact of soil and water conservation practices on soil properties
Watershed intervention implemented in the Kechi micro-watershed has improved the soil condition as a result of reduction in runoff and sediment transport. This is indicated by the significant variations in soil physicochemical properties between conserved and non-conserved plots. SWC structures decreased the slope length and steepness and consequently led to better infiltration, slow movement, and less accumulation of runoff. As a result, the removal of soil particles, crop residues, and other organic components can be limited, which improves the soil condition as compared to the non-conserved soils. The particle size proportion of the soil was fine textured in both conserved and non-conserved soils. The soil of the watershed was dominated by clay content indicating relatively higher mean value in conserved plots. Similarly, Mengistu et al. (2016) reported higher mean clay content in the conserved Minchit than in non-conserved Zikire sub-watershed. Higher soil erosion, removal of fine materials, clay contents, and organic matter could be possible reasons for relativly lower clay content in non-conserved plots. Clay contents are fine particulates and more vulnerable to be washed out by erosion unless treated with SWC measures (Hishe et al. 2017;Selassie et al. 2015). A clay soil has an inherent advantage of good water and nutrient holding capacity and low level of leaching (Osman 2013). This nature of the soil helps the area to be more productive, even though it has been influenced by high soil erosion, continuous cultivation, and other natural and manmade influences. However, significant variation was not observed between conserved and non-conserved plots. This might be related with the prevailing parent materials and its inherent properties; such nature of the soil determines the texture of a soil, even if erosion, deposition, and other human activities may modify (Osman 2013). SWC practices affected the bulk density of the soil in kechi watershed. A relatively higher bulk density in non-conserved plots could be related with washing out of fine organic matter-rich soils by erosion and thereby exposing slightly heavier soil particles. On the other side, several potential causes may explain lower bulk density in conserved plots such as lesser effects of soil erosion (SWC structures as a barrier) and relatively higher SOM content resulted from accumulation of crop residues decay, plant leaves' decay, and less vulnerability for easy removal of this components. The study finding was consistent with the results reported by Hishe et al. (2017)  reported a statistically significantly lower bulk density in Tura plots than in Tuta plots. Soil pH showed slightly higher mean values in Tura plots. Relatively higher soil acidity in Tuta plots may be related with high rainfall, associated with leaching and removal of important soil nutrients. Amare et al. (2013) and Osman (2013) explained that high amount of rain water leaches soluble bases and consequently contributes to soil acidity. Similarly, longterm cropping, high rainfall, topographic steepness, and the application of inorganic fertilizer could probably increase soil acidity (Selassie et al. 2015). The analysis of variance result show that soil pH was not statistically significantly affected by conservation practices (Table 3) ). Soils exposed for severe erosion has been more vulnerable to decomposition of SOC than slightly eroded soils (Abegaz et al. 2016). This implies that non-conserved soils are more vulnerable to erosion and most likely to have low SOC concentration as compared to conserved soils. As a result, supporting SWC structures by agro-forestry practice has been suggested for better carbon sequestration in the soil (Abegaz et al. 2016;Degefu et al. 2011). Similarly, supporting terracing with susbania and elephant grasses could result in high SOC and SOM due to high biomass return, which contributes to symbiotic fixation and soil erosion reduction (Sinore et al. 2018). However, we identified during on-site observation that as an agro-forestry and gully rehabilitation system, eucalyptus tree plantations were predominantly used to limit soil erosion and other related benefits in the study watershed. However, it was reported that the use of eucalyptus tree limits undergrowth and its contribution for SWC has been poor (Fikreyesus et al. 2011) and it is highly nutrient and water consuming species (Wolancho 2015). Hence, there is a need to recommend other better alternative tree plantations in the area. The variation is primarily explained by conservation effects on soil erosion, because soil bund reduces loss of fine soil particles and residues ( who observed insignificant but higher available phosphorous concentration in conserved soils. The concentration of av. P in the soil in kechi watershed was deficient. This could be explained by different factors; the medium acidity nature of the soil and soil erosion through runoff may contribute to its limited availability in the soil. The limited availability of phosphorous in the soil may limit the growth and productivity of plants in the area. Phosphorous in the soil is highly required by plants and may cause slow growth when its concentration is very low (Hishe et al. 2017). The CEC and exchangeable basis content of the soil in the watershed was rated as high. This might be due to the inherent characteristics of the soil because fine textured soils have more exchangeable basis (Osman 2013). Soils having high clay and SOM content have strong probability to hold positively charged ions and consequently hold high CEC concentration (Selassie et al. 2015;Sinore et al. 2018). Conservation measures caused a relatively higher CEC and cation exchange capacity in conserved soils than in non-conserved plots. but the difference did not show statistical significance. Different researchers reported that the effect of SWC measures showed non-significant difference in the CEC content of the soil (such as Hailu et al. 2012;Journal of Resources Development and Management www.iiste.org ISSN 2422-8397 An International Peer-reviewed Journal Vol.74, 2021Hishe et al. 2017). On the other hand, the findings of Challa et al. (2016), Mengistu et al. (2016), and Selassie et al. (2015 reported significantly higher CEC contents in conserved soil. The variation among research reports may be attributed to the level of effectiveness of SWC measures due to variations in conservation types, proper construction, and maintenance. Sinore et al. (2018) reported a significantly higher CEC and exchangeable bases in a soil treated with susbania and elephant grasses than in controlled soil. Supporting terracing with such plants/ grasses strengthens the bund, generates high biomass, and increases OM and better control of erosion, consequently increases CEC in the soil.

The impact of watershed intervention in different land uses
The impact of watershed intervention found to be different in grazing and cultivated land uses. This is indicated by a significant variation in SOC, SOM, TN, exchangeable Na+ and Mg2+ in conserved and non-conserved cultivated land uses and only exchangeable Na+ in grazing land uses. The highest sand fraction was recorded from non-conserved cultivated land and lowest in conserved grazing land. Similarly, Hishe et al. (2017) reported greater sand content in non-terraced farm land. The effect of conservation measures caused greater mean variation of clay content in grazing land uses than in cultivated land uses. The highest (31.3%) and lowest (23.7%) silt content was observed in conserved and non-conserved grazing land uses, respectively (Table 4). This result did not agree with the findings of Hishe et al. (2017) who reported that lowest silt content was recorded in non-terraced cultivated land uses. A relatively lower bulk density, higher SOC, SOM, and total nitrogen were observed in conserved cultivated land than in grazing land uses as compared to their counterpart. Higher SOC concentration was observed in grazing land uses than in cultivated land uses. Abegaz et al. (2016) explained that higher concentration of SOC was observed in cultivated land which makes this land uses to loss SOM more quickly than grazing land uses. The effect of SWC measures has reduced the removal of soil particles, residues, and other organic matter. On the other hand, non-conserved soils are exposed to greater removal of these components that may lead to relatively better effectiveness of conservation measures in cultivated land uses. The analysis result showed that the effectiveness of SWC was better and significant (for some soil fertility indicators) in cultivated land than in grazing land. This might be related with high removal of fine nutrient-rich soil particles due to soil erosion in cultivated land (Belayneh et al. 2019) and conservation structures reduced soil loss in conserved plots. The key informant interview indicated that little or no attention was given for maintenance of conservation structures mainly in grazing land. This is due to communal ownership of most of the grazing land uses and waiting for any community mass-mobilization. On the other hand, the destruction of conservation structures was very high due to year-round open grazing. The result was supported by Wolancho (2015), who stated that controlling watershed intervention in communal grazing lands was poor and its effect was minimal.

The correlation between soil properties
The correlation matrix implies that most of the soil physical and chemical properties vary together. Soil pH had a positive significant relationship with SOM, TN CEC, exchangeable Na+ , K+ , and Ca2+. This indicated that many of the soil properties vary together with soil pH and it determines the availability of other physicochemical properties of the soil and vice versa. The presence of high organic matter, CEC, and basic cations improved the pH of the soil (Sinore et al. 2018). Moderately significant negative relationships were also observed between bulk density and TN, clay content, and basic cations except Ca2+. This could be due to the availability of high organic matter and fine soil particles in the soil (Hishe et al. 2017);Sinore et al. 2018). Principally, the availability of SOM, SOC, TN, CEC, and basic cations showed strong relationship. With respect to this, the implementation of watershed intervention improved most of these soil properties significantly (such as SOC, SOM, TN, and some cations) in this study and other studies (Challa et al. 2016;Hishe et al. 2017;Sinore et al. 2018;Mengistu et al. 2016;Selassie et al. 2015). Therefore, it gives an important lesson that the improvement in SOM, CEC, and clay content can also indirectly influence other properties and rehabilitates the soil to be healthier through its aggregate effect.

Conclusion
Watershed intervention has been an important means to reverse the degraded land and limit further damages to the land resources. They have been a tool for the communities to care for their local environment. This study evaluated the impact of watershed intervention in improving soil physicochemical properties in kechi micro watershed. In this regard, the study revealed that SWC resulted in improvement in soil nutrient content in kechi micro watershed. Soil organic matter, soil organic carbon, total nitrogen, and exchangeable Na+ and Mg2+ showed significantly higher mean values in conserved plot as compared to non-conserved plots. Furthermore, the mean values of soil pH, bulk density, clay content, caution exchange capacity, and exchangeable Ca2+ were better following conserved and non-conserved plots, even if the difference was not statistically significant. Our results also showed that the effectiveness of SWC measures was better in cultivated land than in grazing land. This could be mainly related with poor management and maintenance of conservation structures in grazing land, year-round open grazing with little attention for treatments. SWC practices are effective ways in minimizing soil erosion and improving soil fertility mainly in cultivated lands. However, in general, the issue of continuity (spatial and temporal), maintenance, and reconstruction of structures has been given little attention, which is among the main challenges for limited effect of SWC practices in the watershed.
As a result, regular community mobilization for conservation, assistance, maintenance, and reconstruction of demolished structures needs better attention from the concerned stakeholders, mainly the local government. Since conservation structures were constructed through community mass-mobilization in a campaign form, some individual farmers have been reluctant to retain and maintain structures for long. In addition, supporting SWC structures with grasses and trees is very important for strengthening their effectiveness in improving soil fertility and decrease soil erosion in the watershed.