Technical evaluation of selected soil conservation practices and farmers’ perception about soil erosion in Donbi Watershed, Wolaita Zone, Southern Ethiopia

A study was conducted at Donbi watershed, Wolaita zone, southern Ethiopia to identify, describe and evaluate different introduced soil and water conservation practices and to assess farmers’ perceptions about soil erosion and conservation measures. The necessary data were generated through fi eld measurements and structured questionnaire survey, group discussion and transect walk. The structures were evaluated by comparing the fi eld measurement result with the recommended dimensions. The results obtained showed that level soil bund and fanya juu were the dominant structures identifi ed in the watershed. The technical evaluation of the structures showed that generally the spacing of soil bund was wider than the recommended while in most fanya juus within the acceptable range. Similarly, the channel depth of the structure in different parts of the watershed was smaller than the recommended. Farmers in the watershed are aware of the problem of soil erosion and the importance of conserving soil. They have also developed their own judgments about the relationship between different dimensions of bunds and soil erosion as a result of long fi eld experience in their locality. Research Article Technical evaluation of selected soil conservation practices and farmers’ perception about soil erosion in Donbi Watershed, Wolaita Zone, Southern Ethiopia Bekele Tsegaye1* and Moges Awdenegest2 1Bekele Tsegaye, Areka Agricultural Research Center, Southern Agricultural Research Institute, Ethiopia 2Moges Awdenegest, Department of Bio-system and Environmental Engineering, Institute of Technology, Hawassa University, Ethiopia Received: 27 November, 2018 Accepted: 13 December, 2018 Published: 14 December, 2018 *Corresponding author: Bekele Tsegaye, Areka Agricultural Research Center, Southern Agricultural Research Institute, Ethiopia, Tel: +251911893571, P.O.Box: 79, Areka, Fax: +251465520502, E-mail:


Introduction
Soil erosion is recognized as one of the most serious causes of soil degradation in Ethiopia [1][2][3][4][5]. And hence in highland areas of the country the crop yield and soil fertility levels are extremely low [6]. Annually about 1.5 to 2 billion soil loss rate is reported for the country [7,8]. Most of the factors contributing for soil erosion in the country are human induced [9,10]. Most cultivated lands in the hills and moussntains of the country have suffered from loss of top soil, leaving bare stones. Gullies are observed everywhere in the deep soils [11]. It caused strong environmental impacts and major economic losses from decreased agricultural production and from off-site effects on infrastructure and water quality by sedimentation processes [12,13]. It has put a substantial threat in agriculture of the country. Out of a total surface area of 112 million hectares, the estimates made in the mid 1980s showed that about 27 million hectares are signifi cantly eroded, 14 million hectares are seriously eroded and 2 million hectares have reached the point of no return [5,14].
To mitigate the effects of land degradation, mainly due to soil erosion, the Ethiopian government intensifi ed the effort to improve agricultural production by coordinating farmers to implement soil and water conservation practices [15,16], Declining soil fertility, mainly soil erosion, is one of the most important issues that constrained the agricultural production of both the lowland and highlands of Wolaita zone caused by many combined factors of natural resource management [17]. Pound and Ejigu (2005)  the important wing that should be considered that magnifi es the effectiveness in soil conservation. This is because farmers invest on their land to conserve it based on their perception on both soil erosion and its conservation. Farmers who perceive soil conservation increases crop production felt the responsibility for its conservation [18]. In addition, farmers' decision to adopt soil conservation measures is not only infl uenced by their perception of erosion hazard but also on the types of structures and on their attributes [19]. Therefore the objectives of this study were i) to evaluate the technical aspects and functional status of selected soil conservation practices in reducing soil erosion and ii) to assess the farmers' perception towards the selected soil conservation practices

Description of study area
The study area is located between 6 0 56'1'' to 6 0 56'4'' latitude and 37 0 39'5'' to 37 0 39'3'' longitude in the south western part of the Ethiopian highlands and at altitude between 1908 and 2100 m.a.s.l. and is part of the Omo drainage basin. The landscape of the watershed is mainly characterized by undulating topography with typical slope steepness of 10% to 20%. The total size of the study area is about 165ha.
The climate is classifi ed as sub-humid (Weigel, 1986 cited in Von Gunten, 1993). The mean annual temperature is 20 0 C and the mean daily maximum and minimum are 23 0 C and 17 0 C, respectively. The mean annual total rainfall ranges between 1198 mm and 1762mm. The area has an extended period of long rains with two peaks in the month of April and August [20].
The dominant soil types of the study area is Eutric Nitisol characterized as dark red-brown soil with very deep, well drained and high water holding capacity [21,22]. The area is covered by annual crops thus with poor vegetation cover. However some indigenous and exotic scattered trees and shrubs are found scattered in the area. These trees are found along farm boundaries, stream banks, road sides and at the border of the farmlands.

Data collection methods
There is topographic and farming system variation within the watershed which eventually leads to variation in selection of soil conservation measures. To manage this, the watershed was classifi ed in to three sections as upper stream, middle stream and downstream with major variations in terms of slope steepness and farming system. The watershed has a convex shape surface and hence the upper stream is dominated by homestead and relatively fl at to gentle sloping topography.
The middle section is used mainly for cereal based crop production system. The cereals based crop production system, together with grazing lands, was also practiced in downstream part of the watershed. However, the slope steepness was up to 20% steeper than the other sections. Assessment of soil conservation measures were made in three sections separately to account for the variation due to slope as well as agricultural practices variation. Simple descriptive statistics was applied to analyze data. The data analysis on fi eld measurement was made by comparing fi eld results with the technical standards specifi ed for different topographic and agro-ecological conditions.

Technical evaluation of physical soil conservation measures
The most important and widely used physical conservation measures in the watershed were soil bund and fanya juu which has been implemented since 1980's. In order to evaluate their technical status, performance and preferences by the farmers those with 2 years since their construction for level soil bunds and newly constructed for fanya juu were considered. Implementation of these structures considers agro-ecology, topography, and socio-economic factors [23][24][25] Bund layout, gradient: The bunds considered for evaluation are claimed to be level, made on the contour. However it is common that due to poor layout bunds deviate from being level. The fi eld measurement indicated that in all the selected farm plots, the bunds constructed were not laid along the contour ( Table 2).
Fanya juu: Ditch depth, width and gradient. These are depth and width of basin excavation below the embankment. The depth and width of the ditch for level fanya juu for farmlands with slope steepness up to 10% is about 0.55m and it is 0.6m for farmlands of 10% to 20% slope steepness [23,24]. The fi eld measurement on both of the parameters on the selected farm plots is shown in table 3.

Spacing and vertical interval
The technical parameters selected for evaluation of level fanya juu were spacing, vertical interval, ditch depth and width, embankment bund bottom and upper width, berm size, bund height and bund gradient. Field measurement of spacing

Embankment height, upper width, bottom width and size of berm
These are dimensions related to the fanya juu embankment and their appropriate design is necessary for its better performance of the structure. In addition, these are dimensions that need special technical care because usually there is less participation of farmers in the fi eld in their modifi cation.
The fi eld measurement on all of the indicated parameters on the selected farm plots of the watershed is shown below in the following table. materials. This evaluation was not done for fanya juu due to their short duration after construction and done for only soil bunds.

Farmers' perception of soil erosion related to bund parameters
Farmers were asked to give their opinion on the relationship between the measured bund parameters and soil erosion hazard.
Their response in relation to the effect of bund parameters on soil erosion hazard is indicated in the following table 5. In the upper stream parts of the watershed, the average slope steepness of the selected farm plots is 12.8% (Table 1). Based on the average soil depth, the VI recommended for level soil bund is 1m to 1.2m [23] and 1m to 2m [24]. Therefore, compared to recommended values for such areas, the vertical interval maintained between the consecutive bunds is signifi cantly higher than the recommended one for such farmland types.

Technical evaluation of physical soil conservation measures
For farmland types with such slope steepness and soil depth characteristics, the recommended spacing for level soil bund is 8m to 11m [23]. Similarly, the level bunds in the watershed constructed at wider spacing than the recommended ones for such farmland types.
The average slope steepness of the farm plots in the middle parts of the watershed was varied between 10.78% and 20.45% and the average one is 15.4% (table 1). Based on the average soil depth of the watershed and average slope steepness in this part watershed, the recommended vertical interval of level soil bunds is 1m to 1.4m [10] or 1m to 2m [24]. Like in upper section of the watershed, as compared to the recommended ones, the vertical interval between the consecutive bunds maintained higher in the watershed. The recommended spacing between two consecutive bunds for farm plots with the indicated slope steepness and soil depth characteristics is 7m to 10m.
As compared to the average spacing between the consecutive bunds (Table 1), level soil bunds were constructed with wider spacing than the recommended ones.
For downstream parts of the watershed, the average slope steepness of the farmlands is about 17% which is higher than all the other parts of the watershed. Assuming the maximum vertical interval of 1.5m [23] and 2.5m [24], for such areas, the average value of the fi led measurement result has shown that the vertical intervals of the level soil bunds maintained higher than the recommended ones. For farmlands types with

Bund layout, gradient
The mean gradient of the bunds (21 fi elds in total) in the different sections was ranged from 0.6% to 1.8% ( for such farm plots is about 1m to 2m, and 12m, respectively [23,24]. As compared to these recommendations, both the Gradient of the structure was the other factor that was considered for the evaluation. In all the three parts of the watershed, the structure was not constructed along the contour and it is graded with average slope gradient of 0.12% to 0.91% and it reached the slope gradient up to 3%. Hence, there may be unexpected fl ow following the gradient during intense rainfall.

Farmers' perception of soil erosion related to bund parameters
The  farms. The spacing of the structures were rated as wider than necessary by 68% of the farmers while only 11% of them were saying it is less than what it should be (Table 7). This result is somehow in line with what the fi eld measurement result showed regarding bunds' spacing (especially level soil bund). The embankments height and width were considered just right by 72% and 88% of the farmers respectively. The households' response on the channel depth and width of the structures showed that about half of the respondents indicated both the channel width and depth were just right and in average about 46% of the respondents had no any opinion on both of the parameters. This fi nding interestingly suggested that farmers are more sensitive to the spacing of the structures which affect the width of the cultivable area than the embankments where they claim sizes are acceptable to them.

Conclusions and Recommendation
Both spacing and vertical interval between two consecutive bunds found larger than the recommended ones in all parts of the watershed. Though they have been contributing a lot in preventing soil erosion problem, this deviation resulted in some damages to the bund itself and erosion problems of various levels in the farmlands. However, the good stabilization of the bund with different vegetative materials is appropriate and serves well. But, for the future work in areas of soil bund construction in the watershed improvement should be made regarding spacing and vertical interval for better effectiveness of the structure.
Regarding the level fanya juu, in all parts of the watershed, the vertical interval was maintained around the recommended one. However, in some parts of the watershed, the spacing was wider than the recommended one. Similarly, in all the three parts of the watershed, the ditch depth of the structure was maintained shallower than that recommended one for such watershed types. Therefore, some improvement should be done for the future plan in this regard considering the recommended dimensions for effectiveness of the structure.
Other dimensions such as channel width, embankment height, embankment upper and top width, berm size and gradient of the structure along the contour were generally maintained within the recommended ranges.
Generally, improvement should be made regarding spacing and vertical interval for soil bund, and channel depth and spacing for fanya juu for effectiveness of the structure. In addition, experts should be trained practically regarding dimensions of both soil bund and fanya juu. Farmers in the watershed have good awareness on the effect of soil conservation measures in preventing erosion and they could developed their own judgments up on the relationship between different dimensions of bunds and soil erosion after their long time observation in fi elds. This is a good opportunity for the planners to progress forward in areas of soil and water conservation in the study area.