Soil Erosion Impacts on Crop Productivity and Its Implications on Food Security in Kechabira District, Southern Ethiopia

doi:10.21203/rs.3.rs-3588343/v1

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Soil Erosion Impacts on Crop Productivity and Its Implications on Food Security in Kechabira District, Southern Ethiopia

https://doi.org/10.21203/rs.3.rs-3588343/v1

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Soil erosion has influenced the environmental quality and agricultural productivity of the land. The household survey and combined geospatial techniques were applied to carry out the research. The SRTM digital elevation dataset was used for morphometric analysis of relief and drainage systems in the study area. Landsat 4-5-TM C₂L₂ images between 2005–2020 were applied for analysis of land use and land cover dynamics. Furthermore, FAO/USDA Soil map of the world was used for soil classification, and soil laboratory analysis was also taken place to find out the depletion of soil micronutrients by soil erosion. Results of morphometric analysis revealed that the topographic nature of the surface, slope gradient of the area, drainage feature of rivers and land use/land cover conditions of soil surface are found to be facilitating factors of soil erosion in the district. Most of the respondents also confirmed that over cultivation, cultivation of steep slopes, deforestation, over-grazing, unreliable soil management practices and poor agricultural techniques are the main causes for the prevalence of soil erosion in the study area. About 91% of the interviewed households have observed a decline in the productivity of land in their farm field. Similarly, the crop productivity per hectare for selected dominantly produced crops decreased over 5 cropping years between 2013–2017. According to soil laboratory analysis, the soil of the study area is characterized by moderately acidic, low category of OM and organic carbon content, low proportion of available phosphorus and very low to low range of total nitrogen. Most of the surveyed households are food insecure due to loss of agricultural productivity by soil erosion. It is recommended that combating the severity of the soil degradation problem by applying various soil management practices should be critically considered.

Physical Geography

Agricultural Economics & Policy

Soil Erosion

Crop Productivity

Food Security

Agriculture

Land Use Land Cover

Land degradation is currently remaining one of the serious global problems because of its adverse impact on agricultural productivity, food security and environmental sustainability. Due to land degradation in the form of soil erosion in most developing countries, in particularly agricultural productivity declined beyond the subsistence requirement of a household (Gebremariam et al., 2010). Soil erosion is a critical global land degradation phenomenon affecting human beings since human’s basic sources of livelihood are from the land (P.U. et al., 2017). Degraded soil is unproductive, which is also determined by the degree of severity to land damage. Soil erosion affects between 25–30 percent of the total land under cultivation in India (Chopra, 2016). In Africa over 70% of the nation’s land surface has been impacted by varying levels and types of soil erosion (Thiombiano & Tourino-Soto, 2007). On a global scale, the Food and Agriculture Organization (FAO) estimates that the loss of productive land through soil erosion globally is about 5–7 million ha/year (FAO, 2006).

Soil erosion can cause the gradual detachments of particles of top-soil which are transported by agents of denudation, such as water and wind, and subsequently deposited in low basin areas (P.U. et al., 2017). According to (Aberha, 2008), the implication of soil erosion extends beyond the removal of valuable soil nutrients from topsoil. In fact, crop emergence, growth and yield are directly affected through the loss of natural nutrients which results with food security (Pimentel & Burgess, 2013). Hence, currently soil erosion problems have taken much attention by different scholars and scientists in the area of environmental concern.

Future world population requires increased food production because of rapidly growing world population that needs the increased agricultural production to feed the population (Kumar & Mohanta, 2003). On the other hand, the resources of land have been under alarming rate of degradation due to human abusive actions causes the reduction of land resource productivity to grow substantial foods for additionally growing world population (Pimentel & Burgess, 2013). If the growth of population goes on beyond the carrying capacity of the environment, the needs of human population cannot be fulfilled from natural resources. Hence, the damages on soil resources through soil erosion and in any other forms soil degradation can result with the damages to agricultural production and ultimately causes food insecurity.

Statement of the problem

The most pressing environmental problem in the least developed countries are prevalent in rural areas, where large number of populations live and whose livelihood depend on agriculture and related activities (M. Getachew, 2014). Large areas of sub-Saharan African countries in particular are highly affected by various types of land degradation, which directly cause the decline in soil fertility (Mushir & Kedru, 2012). Inappropriate land resource conservation practices in areas with high population density and fragile ecosystem further increases loss of productivity of land resources. These in turn affect food security and livelihood. The productivity of land in Africa has declined by 50% due to soil erosion and desertification (Thiombiano & Tourino-Soto, 2007). Yield reduction in Africa due to past soil erosion may range from 2–40% with a mean loss of 8.2% for the continent (Getachew Tesfaye Ayehu, 2013).

Since Ethiopia is less developed country, the economy and livelihood for the majority of the population are generated from land resources such as land, water and forest resources. Declining land productivity, natural resource degradation, high population growth and food insecurity are a crucial challenge facing Ethiopia today (Bekele & Drake, 2003). There is direct link between the most basic need of human beings and natural resources in Ethiopia (Dubale, 2001). On the other hand, agriculture is the predominantly an important economic sector in Ethiopia which support about 85% of the rural population (Dubale, 2001). Agriculture provides about 52% of the country`s gross domestic product, 80% of its employment and 90% of its export earnings (World Bank, 2010). The type of agricultural economy in the country is characterized with subsistence in nature and crop and livestock farming are principal practices in the sector. such subsistence agricultural economy results with excessive soil erosion and land degradation (Mengstie, 2009).

Soil degradation is the most immediate environmental problem facing Ethiopia, especially high land areas of the country. Soil erosion in Ethiopia can also be seen as a direct result of past agricultural practices mostly in the high land areas of the country. More than 80% of human population and 90% of total agricultural production are located at high lands of Ethiopia (Nyssen et al., 2015). The high land areas have been experiencing severe land degradation problems emanating from the demands of the growing human and livestock populations (Ertiro, 2006). Decline in agricultural productivity in high land has largely been associated with high population density, deforestation and intensive cultivation of steep slopes without effective conservation measures (Bishaw, 2001). According to research findings in Ethiopia, land resources are under intense challenge due to rapidly growing population and inappropriate farming practices (Mushir & Kedru, 2012). Soil erosion is greatest in cultivated land where the average loss is 42 tons /ha, compared with five tons/ha from pastures. As a result, nearly half of the soil loss comes from land under cultivation (Hurni et al., 2010). So that the decline in agricultural productivity of the country is directly linked with loss of top soil and the deterioration its fertility.

Similarly, population pressure, over cultivation, overgrazing, deforestation and other related problem are identified as the main factor for soil erosion in Southern Ethiopia (Ertiro, 2006). Soil erosion is a serious problem in the central zones of the Southern Ethiopia such as Kambata Tambaro, Hadiya, Wolaita, and Alaba including study district with their sloppy nature of the area and an excessive cultivation of the land due to high pressure of the population of the area. There is an urgent need of identifying the serious problem of soil erosion which directly results with land degradation, loss of land productivity and food insecurity. So that understanding current status and causes of soil erosion and its effects are going to be important to bring environmentally sustainable development. The watersheds and river catchments of the district were highly degraded due to excessive tillage by their high number of population and mismanagement of land resources which result with soil erosion and soil fertility decline in the study area. Therefore, this study focuses on assessing the impacts of accelerated soil erosion on crop productivity which result with food insecurity in Kechabira district at Kambata Tambaro zone, Southern Ethiopia.

Location of Study Area

Kachabira district is located in Kambata Tambaro zone, SNNPR, Ethiopia. It is bordered by Doyogana district to the North, Boloso Sore district to the South, Kadida Gamela district to the East and Hadera Tunto Zuria district to the West. Geographically, the study area is located between 7º10ꞌ 00ꞌꞌN -7º 20' 00"N and longitudinally it is located 37º 39' 30"E − 37º 51' 30"E (Fig. 1)

Sources of data

The study has been used two data sources for collecting research data. These were primary and secondary data sources. The primary data were collected from farmers, agricultural experts, kebele leaders, soil and water conservation supervisors and DAs’. The secondary of data sources used for the study include published materials such as research articles, books and data files from internets or web pages, and unpublished documents such as official records, census records, project reports and other official data For geospatial and image analysis, topographic maps, SRTM digital elevation data, FAO/USDA Soil map of world and land use land cover data of FAO Map Catalog are used as secondary sources of data.

Data gathering instrument

Detailed information on house hold demographic characteristics, soil erosion impacts, land characteristics, agricultural productivity, food security status and other related information were collected by using questionnaire, focus group discussion and interviewing. Moreover, personal observations and informal interview were also done through transact walk. Finally, the researchers had used soil sample experiments to identify the productivity of soil from selected sample areas for laboratory analysis of essential macronutrients and micronutrients.

The sample size and sampling procedures

The study had considered the law of probability for sampling study site and sample population. Therefore, two-stage sampling designs were used to determine sample villages and household heads. In the first stage, the sample kebeles from the study area were selected. Kechabira district contains 16 Kebeles. From the total 16 kebeles of the district two Kebeles namely Mino and Zogoba were selected randomly for household survey and soil sample collection.

The second stage involves preparation of a list of household heads from each selected Kebeles. Hence, the size of household heads in sampled Kebeles (Mino and Zogoba) were 2121 household heads. Out of total household heads, 121 sample household heads were selected using systematic random sampling techniques.

Soil Sampling and Laboratory Analysis

The soil sample for analyzing soil nutrient in the district was collected from sample soil fields by considering simple random pattern across the field uniform fields. The Sites for soil sample were selected by using global positioning systems (GPS). A total of six soil samples were collected randomly from two selected kebeles from 0–20 cm depth. About 5 to 10 sub-samples from each field were taken to form one kg composite sample. The sample was collected by sampling tools like Corer of 50mm steel tubing and a stainless-steel soil sampling probe. The soil probe provides a continuous soil core with minimal disturbance to the soil that can be readily divided into various sampling depths. Other tools include the plastic sample buckets, shovel or spade, sample bags, and markers for identifying samples on sample bags.

After soil processing (drying, grinding and sieving), soil physicochemical properties such as texture, pH, soil organic carbon (OC), Bulk Density and Soil macronutrients such as nitrogen (N), phosphorus (P), potassium (K) and Sulphur (S) were tested and analyzed to identify nutrient status of soil. Determination of particle size distribution was made by Hydrometer (Bouyoucos) method as described by (Robert Okalebo et al., 2002). The bulk density of soil was determined by the core method. Soil pH was determined using pH meter with combined glass electrode at 1:2.5 (soil: water) ratio. The organic carbon was determined by the Walkley and Black method (1934) as cited at(Minase et al., 2016) and organic matter was multiplied by1.724 value with organic carbon percentage. The total N content of soil was determined by using the Kjeldahl procedure and available P was also determined by using Olsen method (de Silva et al., 2015).

Methods of analysis

The data were analyzed both qualitatively and quantitatively. The household survey data were coded and entered into Statistical Package for Social Scientists (SPSS). Then, computation of frequencies and percentage were demonstrated using.

Morphometric Analysis

Morphometric analysis of aspects of relief features such as topography and slope gradient were described and evaluated for identifying the effects of slope and related morphometry of the land features on occurrence of soil erosion in the district. Moreover, the morphometrics of drainage system of rivers of the district were analyzed by using SRTM DEM with the use of TNT Atlas 2013 software. The Bifurcation Ratio (Rb) of the stream order are computed using law of stream numbers and orders (Horton, 1945) to find out the ratio for stream orders and the risk of soil erosion.

Analysis of Land Use/ Land Cover dynamics

The land use/land cover change conditions of the district were analyzed by considering 25 years land use/land cover satellite images of 2005, 2015 and 2020. The Supervised classification techniques of images by using Arc GIS 10.8 version were applied for analyzing land use/ land cover change of study area. For the detection of land use/ land cover dynamics in the study area, Landsat 4-5-TM C₂L₂ image of between 2005–2020 were drawn from USGS Landsat data sets and analyzed accordingly.

Topography of the district

The topography of the study area is generally characterized by plain, plateau, ridges and rugged terrain which are the extension of the Hambaricho Mountain. The Hambaricho Mountain is the highest mountain in the region with the elevation of 3025m above mean sea level. The altitude of the study district lies between 1619–2701m above sea level (Fig. 2). The contour and hill shade maps in the figure below shows that the terrain features of the district are mostly occupied with hills, various ups and down, and river gorges which are formed by rivers and run-off in past long history of land form formations. This unstable terrain features of the area have an exacerbating effect on soil erosion rates in the farm field of study area. Therefore, the relief feature with its sloppy nature of the area considered to be one factors for occurrence of soil erosion in combination with human’s abusive actions taken place in the area.

Slope features and its effects

Slope is defined as the inclination of the land surface from the horizontal (USDA & NRCS, 1999). Slope in percentage is calculated by dividing vertical distance by horizontal distance and, then multiplied by 100. The Slope of study area is discussed by classifying into five slope classes based on percentage of slope gradient (Fig. 3). These are slope gradient between 0–3%, 3–8%, 8%-15%, 15–30% and > 30% according to the size of study area. Generally, the slope gradient of study area is found between 0% to greater that 40% of which majority of land area lies between 3–8% of slope gradient. Out of the slope classes, about 68% of land surface of the study area are at 3–15% slope gradient and 22% of land area is occupied under 0–3% slope classes.

Therefore; according to slope classes of USDA Natural Resources Conservation Service, the most part of study area is categorized as undulating and strongly sloping or rolling slope classes (USDA & NRCS, 1999). Slope has a significance role in farming process and for landowners, because it influences erosion potential. Steeper slopes aggravate the rate of erosion through runoff when precipitation reaches the soil.

The University of Wisconsin Extension finding on agricultural studies suggests that soil slopes that exceed 2% are typically eroded if cultivated (Deller & Williams, 2011). Contrary to this, all slope categories in Kechabira district including steep mountain tops and deep gorge areas are under process of cultivation (Fig. 4). So, that it is concluded that the slope nature of the land area and the cultivation of undulating to steep slope soil surface in the district can be assumed to be causes for occurrence of soil erosion in the study area.

On the other hand, household survey on the farm plots of cultivation lands in the study area also that out of total sample plots about 40% farm plots area moderately and 32% are steeply sloping farm plots (Table 1). This also indicates that still farmers of study area are engaged on cultivation of soil surface which are highly exposed to soil erosion.

Table 4.1

Slope of cultivation field
Slope Farm Plots	Frequency	Percent
Flat	26	21.5
Undulating	7	5.8
Moderately Sloping	49	40.5
Steeply sloping	39	32.2
Total	121	100.0

Source Household Survey, (2019)

Drainage Feature and its effects on Soil Erosion

In the district, there are various streams and a greater number of perennial rivers. The rivers of study area drain towards the Ajora Fall via Omo River. Ajora fall is the most tremendous twin water fall in Ethiopia. The twin is formed by two major rivers Ajacho and Soke. The main perennial revers of the district are Ofute, Sanbata, Ketala and Ajacho rivers starts from the high lands of the district. The rivers in their upper course are joined by the plenty number of small streams (Fig. 5). In the upper course, the rivers passe steep slope and undulating slopes by forming gorges and rapids which accelerate rapid loss of soil in hill sides of the district in which agricultural activities are parallelly dominate. Moreover, the river network densities are also greater in the district which ultimately facilitate rapid loss of soil resources.

The Strahler stream ordering map indicates that the main rivers of the study district are made of more than 3 order of streams and maximum streams order is 4 orders in one of big river which cross the central part of the district (Fig. 6). Based on Strahler stream numbering and ordering system, the mean bifurcation ratio of the stream order was calculated to identify the relationship between the number of streams of first order and those of the next higher orders. Accordingly, the mean bifurcation ratio of drainage is 3.3 which is at lower level of mean ratio. The mean ratio indicates that the risk of soil erosion is potentially greater due to higher frequencies of rivers at first order streams. Therefore; the drainage feature of the district is also the main exacerbating factor for soil erosion.

Mean Bifurcation ratio=\(\frac{B1+B2+B3}{3}=\frac{5+2+3}{3}=3.3\)

Land uses/ land cover Dynamics and its effects on soil erosion

According to land use/ land cover detestation and analyzed by using geo-spatial techniques, the dominant types of land use land cover observed in the study area are crop lands, settlement, grass lands, forest lands and bush lands (Fig. 7).

Although the total share of land area varies among land use types, the major kinds land use land cover during 2015–2020 in their sequential order are crop lands, settlement and forest lands (Fig. 8 and Fig. 9).

The major land use land cover types during 2005 in sequential order are crop land covers 165 km² of land, grass lands covers 58km² and settlement covers 3km² of land (Fig. 10).

Concerning to dynamics of land use/ land cover in the study area, crop and grass lands have shown decreasing trends while settlement, forest and bush lands have shown increasing trends during 2005–2020. As indicated in Table 2 below, the crop lands decrease by 20% and grass lands decrease by 25% in past 25 years in the district. But settlement lands increase by 40% and forest land increases by 4%. These shows that there are increasing of settlement due to expansion of urbanization and unplanned informal urban settlement around peri urban areas by replacing former crop lands in the district. During household survey and discussions with key informants, it was also found that the crop lands are replaced by bush land whenever the cultivation lands are degraded due to loss of soil productivity by soil erosion. Thus, bush lands are relatively increasing in the study area mostly around eroded rivers sides and hilly areas. Similarly, it was also observed that some farmers were forced to shift their cultivation lands in to agroforestry when farm lands are degraded which on the other hand result with the increase of forest land in the district. The grass lands in the study area are declining due to the expansion of crop and forest lands to grazing grounds and expansion of settlement as well.

The land use land dynamics of the district is the implication for the occurrence of soil erosion. As it was discussed earlier, some of land use/ land cover types are changed due to land degradation by soil erosion like changing of cultivation land in to bush and forest lands. On the other hand, it is also found that the prevalence of soil erosion is used as a reason for expansion of some kind of land use/ land cover like the settlement land which causes the disturbance of land surface result with soil erosion.

Table 2

Observed land Use/ land cover changes
No	land use/ land cover types	Area coverage in km²			Observed Change (%)
No	land use/ land cover types	2005	2015	2020	2005–2015	2015–2020	2005–2020
1	Crop Land	165	155	119	Decrease by 4%	Decrease by 16%	Decrease by 20%
2	Grass Land	58	4	1	Decrease by 24%	Decrease by 1%	Decrease by 25%
3	Settlement	3	62	93	Increase by 26%	Increase by 14%	Increase by 40%
4	Forest Land	0	4	8	Increase by 2%	Increase by 2%	Increase by 4%
5	Bush land	0	0	4	No change	Increase by 2%	Increase by 2%
6	Water Body	0	0	0	No change	No change	No Change

Source: FAO land cover classes (2005-2020)

Nature of Soil and its effect on soil Erosion

Soil of the study area is derived from highly weathered rocks, mainly sedimentary rocks and basalts. The dominant types of soils covering the study area are Eutric Nitosols, Ochric Andosols and Plinthic Ferralsols. Of these soil types Eutric Nitosols are the major soil types covering large area of the district (Fig. 11). By nature, Nitosols are deep, well drained and red colored tropical soil with defused horizon boundary. They are strongly weathered soil with high rate of erodibility in intensified agricultural soil. The soil textural class is categorized under clay type with 47% clay, 26% and 27% sand fractions.

Farmers also identified soil color of the study area as black 35.5%, reddish 46.3% and brown 18.2% (Table 4.13). Generally, soil color in the study area is dominated by reddish color.

Table 3

Soil color of cultivation
	Variables	Frequency	Percent
Soil color	Reddish	56	46.3
	Brown	22	18.2
	Black	43	35.5
	Total	121	100.0
Source: Household Survey, (2019)

Soil Physical Properties

Soil Texture

The laboratory results of soil textural classes indicates that particle size distribution of samples from six soil samples are dominated by clay fraction with mean value of 54% clay, 20% silt and 26% sand textures (Table 4).

Soil bulk density

Soil bulk density (BD) of study sample areas is ranged from 1.23 to 1.25 gm /cm³ with an average value of 1.235 gm /cm³ (Table 4). Bulk density is an indicator of soil compaction. According to Hazelton and Murphy (2007) cited at (Laekemariam, 2016), the critical BD value for clay texture soils is 1.4 gm /cm³, most rocks have a bulk density of 2.65 gm /cm³ and for medium textured soil with about 50 percent pore space have a bulk density of 1.33 g/cm3. But the value of bulk density in the district is lower compared with critical bulk density value for clay texture soil. This shows that the soil of study area is loose, porous and not compacted which is most susceptible for occurrence of soil erosion.

Table 4

Soil Texture and bulk density
No	Soil Sample Sites	Textural Fraction (%)			Texture Class	BD (gm /cm3)
No	Soil Sample Sites	Sand	Clay	Silt	Texture Class	BD (gm /cm3)
1	Zogoba kebele, 01	28	52	20	clay	1.24
2	Zogoba kebele, 02	26	54	20	clay	1.23
3	Zogoba kebele ,03	30	52	18	clay	1.25
4	Mino kebele, 01	24	54	22	clay	1.23
5	Mino kebele, 02	24	56	20	clay	1.23
6	Mino kebele, 03	24	56	20	clay	1.23
Mean Value		26	54	20	Clay	1.235
Source: Soil Laboratory experiment output, (2019)

Soil Chemical Properties

The chemical properties of soil are the levels and availability of nutritional mineral elements for the plants, and the chemical parameters of soil in connection with their restoration or availability. Soil chemical properties include soil pH, cation exchange, base saturation, salinity, sodium adsorption ratio, enzymes, and electrical conductivity. These properties affect processes such as nutrient cycling, biologic activity, soil formation, pollutant fate, and erosional processes (Alemu et al., 2016). Hence, to find soil chemical properties soil macronutrients such as phosphorus, nitrogen, carbon, calcium, magnesium, sodium, potassium and sulfur are tested and analyzed (Table 5).

Soil pH

Soil pH refers to a soil’s acidity or alkalinity and is the measure of hydrogen ions (H+) in the soil (Robert Okalebo et al., 2002). The soil pH highly affected by soil erosion. The soil experiment result in the sample area shows that soil pH is found between 5.06–7.05 with mean value of 5.85 (Table 5). The average value of pH indicates that the soil of study area is moderately acidic. On the other hand, about 33% of sample area were found under strongly acidity (pH < 5.5) and 50% sample sites were moderate acidity (5.6–6.5) and 17% of areas were alkaline (G. Getachew & Mamo, 2019). The observed pH value in the study area is associated with removal of bases through top soil erosion and leaching by strong rainfall.

Soil organic carbon (OC)

The OC content soil in the study sites vary between 0.93–1.56% with mean value of OC is 1.22%. (Table 4.15). According to soil organic carbon rating cited at the research finding by (G. Getachew & Mamo, 2019), the ranges of soil OC content in the study area is fall under low to very low which is < 2%.

Total N (TN)

The total nitrogen contents of soils in the study area vary between 0.066–0.132% with mean value of 0.084% which shows that the Total Nitrogen content of the soil lies under very low to low according to EthioSIS (2014) cited at (Balasubramanian, 2017). The very low to low range of TN in the study area is attributed to complete removal of biomass and organic content of soil due to intense cultivation and soil erosion (Table 5).

Available P

The available phosphorous contents of soils in the research are is ranging between 0.32-5.48ppm (Table 5). The mean value of available phosphorus is 3.01ppm which shows the very low to low range of content compared with the critical limit description established by Cottenie (1980) cited at (Getachew, 2014).

Soil Organic Matter

The organic matter of soil ranges between 1.603–2.689% with mean value of 2.095%. Hence, according to M. Getachew (2014), all soils of study area are classified as low in their OM contents. This is mostly due to loss of top fertile soil by intensified cultivation practices and soil erosion prevalence in the study area.

Electrical Conductivity

The electrical conductivity values of soils of study area according to Ethio SIS (2014) cited at (Balasubramanian, 2017), shows that soils of study area are salt free (Table 5).

Table 5

Soil Macro-nutrients and Chemical properties
No	Soil Sample sites	pH (1:2.5)	EC (µS/cm)	% TN	Available P (ppm)	% OC	% OM
1	Zogoba kebele, 01	5.91	47.8	0.118	3.06	1.43	2.465
2	Zogoba kebele, 02	7.05	42.2	0.097	2.19	1.25	2.155
3	Zogoba kebele ,03	5.06	42.9	0.132	5.48	1.56	2.689
4	Mino kebele, 01	5.37	58.8	0.089	0.32	1.15	1.983
5	Mino kebele, 03	6.04	50.6	0.072	5.64	0.97	1.672
6	Mino kebele, 02	5.72	54.5	0.066	1.39	0.93	1.603
Mean Value		5.85	49.46	0.084	3.01	1.22	2.095
Source: Soil laboratory Experiment result, (2019)

Causes of Soil Erosion

The household survey result shows that soil erosion mainly caused by over cultivation, cultivation of steep slopes, clearing of forests, over grazing, overcultivation and Poor agricultural practices (Table 6). It is also found that, soil erosion is caused by other facilitating factors such topographic nature of the surface, slope gradient of the area, drainage feature of rivers and land use/ land cover conditions of the area. Due to the above listed causes, soil erosion can affect the production potential of the land, livelihood of households and environmental quality.

Table 6

Causes of soil erosion
Causes of soil Erosion	Ranks in percentage
Causes of soil Erosion	1st	2nd	3rd	4th	5th	6th
Deforestation	12	10	70	11	10	20
Over grazing	31	33	13	57	22	13
Over cultivation	67	19	29	22	6	5
Poor agricultural practices	15	14	10	39	59	17
Cultivation of steep slopes	12	65	7	8	23	16
Other factors	10	11	17	10	27	76
Source: Household Survey, (2019)

Severity of Soil Erosion

All respondents in the study acknowledged that soil erosion as a problem at least in one of their plots (Table 7). According to key informants during focus group discussion, the indicators of soil erosion include decrease in the capacity of soils to grow a variety of crops, decrease in the depth of top-soil, decline in water holding capacity of soils, decline in yield from the farm, etc. In addition, households were also interviewed about the severity of soil erosion in their farm plots. Thus, about 79% and 21% of the respondents acknowledged that severity of soil erosion risk in their farm field is severely and moderately severe respectively (Table 7). The remaining (9%) of farmers rated the problem to be minor on their farm plot. From the result one can conclude that soil erosion is the serious problem in the study area.

Table 7

Respondents view on soil erosion
Variables	Options	Frequency	Percent
Soil Erosion	Yes	121	100
Soil Erosion	No	0	0
Erosion Severity	Severe risk of soil erosion	79	65.3
	Moderate risk of soil erosion	21	17.4
	Minor risk of soil erosion	11	9
	No risk of soil erosion	6	5
	Others	4	3.3
	Total	121	100.0
Source: Household Survey, (2019)

Consequences of soil erosion

Regarding the consequences of soil erosion, about 68% of respondents forwarded that land productivity (yield) decline, change in type of crops grown and reduces farm plot size by declining land productivity are the main consequences of soil erosion (Table 8).

Table 8

Consequences of soil erosion
	Options	Frequency	Percent
Variables	Land productivity (yield) decline	11	9
	Change in type of crops grown	10	8
	Reduces farm plot size by declining land productivity	18	15
	All	82	68
	Total	121	100.0
Source: Household Survey, (2019)

Impacts of Soil Erosion

Soil Erosion Impacts on soil quality

Out of total respondents interviewed concerning the fertility status of soil, 78.5% of respondents confirmed that fertility of soil in the study area is declining. But very limited number of respondents answered that fertility of soil is the same through time interval (Table 9). On the other hand, majority of respondents (89.3%) also forwarded that the decline of agricultural productivity is one of the most important indicators for loss of fertility in the study area (Table 9). Regarding soil fertility decline, majority of respondents (55%) replied that loss of top soil by erosion is the major causes for soil fertility decline. Other reasons for soil fertility decline in the study area include over cultivation and over grazing (Table 9).

Table 9

Fertility of Soil
	Options	Frequency	Percent
Fertility status	Improving	4	3.3
	The same	22	18.2
	Declining	95	78.5
	Total	121	100.0
Indicators of fertility decline	The decline of agricultural productivity	108	89.3
	Devoid of vegetation cover	3	2.5
	Size and color of seedlings	10	8.3
	Total	121	100.0
Reasons for fertility decline	Losses of top soil by erosion	67	55
	Over cultivation	34	28
	Over grazing	20	17
	Total	121	100
Source: Household Survey, (2019)

Soil Erosion Impacts on Changes in land productivity

As it is discussed in Table 10 below, about 91% of the interviewed households have observed the decline in the land productivity land over the last 5 years and 9% respondents having not observed any changes. In relation to decline in land productivity, majority respondents (88%) responded that the productivity of land is decreasing from time to time in their farm field (Table 10). The reasons responsible for the decline in land productivity are soil erosion and loss of soil fertility as responded by majority of respondents. This result indicates that farmers of study area are influenced by shortage of production.

Table 10

Change in crop productivity
	Options	Frequency	Percent
Change	Yes	110	91
	No	11	9
	Total	121	100
Types of change	Decreasing from time to time	106	87.6
	Increasing from years on ward	6	5.0
	Neither increasing nor decreasing	9	7.4
	Total	121	100.0
Reasons for change	Decline in soil fertility	16	13
	Soil Erosion	40	33
	Both	65	54
	Total	121	100.0
Source: Household Survey, (2019)

Soil Erosion Impacts on Yields of cultivatable crops

The croplands in the district are planted to annual food crops, including cereals (Maize, Wheat, Teff and Sorghum), pulses (Haricot beans, Beans and Peas), root crop and cash crops(Abiyo et al., 2018). As it is shown in Fig. 12 below, the crop productivity per hectare for selected dominantly produced crops in the study area is decreasing in past five years. The amount of productivity of Teff per ha in past 2005 E.C was 27kg/ha but it was declined to 23.5kg/ha in 2009 E.C. This refers to that the amount of productivity is declined by 13% in past five years. Similarly, the amount of wheat productivity declined by 12%, Maize by (5%) & Enset by (7%). According to focus group discussion with the selected stakeholders of the kebele members, major causes for declining of crop productivity in study area were continuous occurrence of massive erosion, climate variability and unwise land management.

Implications of Soil Erosion on Food Security

The chief impact of soil erosion, mainly depletion of productive capacity of land under cultivation has effect on food security (Thesis & Aberha, 2008). Cultivating marginal land exacerbates the problem through further altering of land forms and changing land use. Soil erosion means that households have to invest additional expenses to purchase chemical fertilizers (Ertiro, 2006). Table 11 below shows the respondents’ views on the effect of soil erosion on food security and the indicators of food security in the study area. The majority of the respondents (79.3%) reported that they were food in secured. As it was revealed by focus group discussion, the farmers of study area were seriously affected by reduced numbers of daily meals, reduced quantity of food per meal, withdrawal of children from school and marginal land cultivation had to be adopted.

Regarding to the reasons for food insecurity, about 46% of respondents answered that soil fertility decline due to soil erosion is one of the major factors for food insecurity in the study area. Moreover, 24% of respondents answered that food insecurity is caused by shortage of productive land. But very little number of respondents (10%) forwarded that rapid population growth is one of the factors for food insecurity (Table 4.21). Therefore; it is clear that the effect of soil erosion on livelihoods by affecting soil fertility of farmers in the area is one the reminding problem.

Table 11

Food security status
Variables	Options	Frequency	Percent
Food Security	Food secured	25	20.7
	Food in secured	96	79.3
	Total	121	100.0
Reasons for food insecurity	Soil Fertility decline due to erosion	55	45.5
	Shortage of productive land	29	24.0
	Rapid population growth	12	9.9
	Total	121	100.0

Source: Household survey, April 2017

Soil erosion is a threat to the economic development of southern Ethiopia as it affects the agricultural sector significantly. The main sources of incomes for household in the study area are sales of crop production and animals. The farming system was characterized by small-scale subsistence mixed farming-system, with livestock production as an integral part. Crop production was mainly rain-feed. Almost all croplands are planted to annual food crops, including cereals pulses and cash crops. About 97% of households cultivate less than 1ha of land. The dominant types of soils covering the study area are Eutric Nitosols, Ochric Andosols and Plinthic Ferralsols. The contour and hill shade maps analysis of terrain features shows that the study area is mostly occupied with hills, various ups and down, and river gorges which were formed by rivers and run-off in past long history of land form formations. The slope gradient of study area is found between less than 3% to greater that 40% of which majority of land area lies between 3–8% of slope gradient. According to Strahler stream ordering and numbering system, the study area is made up 4 orders of streams with mean bifurcation ratio of 3.3. The analysis of three period of land use land cover types during 2005, 2015 and 2020 by using geo-spatial techniques shows that crop lands, settlement, grass lands, forest lands and bush lands are dominant types of land use land cover observed in the study area. The land use land cover dynamics of in the study area indicates that crop and grass lands have shown decreasing trends while settlement, forest and bush lands have been showing increasing trends during 2005–2020. The soil laboratory experiment result indicates that the particle size distribution of soil in study area is categorized under clay textural classes and soil bulk density (BD) is found at the range from 1.23 to 1.25 gm /cm³ with an average value of 1.235 gm /cm³. Moreover, it is also analyzed that soil pH is found between 5.06–7.05 with mean value of 5.85, OC content of soil vary between 0.93–1.56% with mean value of OC is 1.22%, total nitrogen contents of soils vary between 0.066–0.132% with mean value of 0.084% and organic matter content of soils is found at the range between 1.603–2.689% with mean value of 2.095%. About 65% of respondents in the study area confirmed that degree of soil erosion in the farm field is severe. The perceived main causes of soil erosion in the study area are over cultivation, cultivation of steep slopes, poor agricultural practices and deforestation. It is also found that, topographic nature of the surface, slope gradient of the area, drainage feature of rivers and land use land cover conditions are found to be the potentially facilitating causes for occurrence of soil erosion in the study area. The main consequences of soil erosion in the study area are decline in land productivity, change in type of crops grown and reduces farm plot size by declining land productivity. It is also analyzed that soil erosion has impacts on land productivity, yields of crop and soil quality or nutrient loss in the soil. It is confirmed that productivity of crops per hectare per year for selected dominantly producing crops in the study area is decreasing in past five years. The amount of productivity of teff declined by 13%, wheat by 12%, Maize by (5%) & Enset by (7%). The majority of the respondents in the research area are reported to be food in secured. The main reason for food security is found to be loss of agricultural productivity due to soil fertility decline by soil erosion, shortage of productive land and rapid population growth.

Recommendation

In order to combat the soil erosion problem and enhancing crop productivity in the coming future in the study area, the following recommendation should be critically considered.

The severe soil erosion in the study area directly accelerated soil degradation and declines the productivity of land in the area. Thus, combating the soil erosion problem by applying a wide range of soil management practices and creating skillful awareness to farmers of the area should be recommended. In addition, there should be need of formulating appropriate plan and strategies for creating awareness among farmers of the area to avoid the problem of deforestation and implementation of reforestation program.
The soil laboratory test result reveals that the soil of study area is characterized by moderately acidic, low category of OM content, very low to low range of available phosphorous and very low to low range of total nitrogen. Therefore, concerned stakeholders should improve the acidity nature of soil by adding carbonate minerals and enhancing organic matter content of soil by developing and applying composts and organic decompositions.
The prevalence of drought due to shortage of rainfall and an increase of temperature in recent decades result with decline of production and loss of formerly available root crops like sweat potato, yam and Ensat. Therefore, the impact of climatic variability on crop production and loss of crop species should be assessed by researchers in the study area.

Conflict of Interests

The author has not declared any conflict of interests on this research work.

Acknowledgements

The author would like to express the sincere thanks to Wachemo University Office of Research and Community Service Vice president for financial support of the research work. I would also like to thank the Research and Community Service Directorate office of Durame Campus for material support and facilitation of the research activities. Furthermore, my thanks also extended to farmers and Agricultural offices of Kechabira district for their assistance in providing information and relevant research data.

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Soil Erosion Impacts on Crop Productivity and Its Implications on Food Security in Kechabira District, Southern Ethiopia

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Abstract

Figures

Background of the study

Statement of the problem

Research Methodology

Location of Study Area

Sources of data

Data gathering instrument

The sample size and sampling procedures

Soil Sampling and Laboratory Analysis

Methods of analysis

Morphometric Analysis

Analysis of Land Use/ Land Cover dynamics

Results and Discussion

Topography of the district

Slope features and its effects

Drainage Feature and its effects on Soil Erosion

Land uses/ land cover Dynamics and its effects on soil erosion

Nature of Soil and its effect on soil Erosion

Soil Physical Properties

Soil Texture

Soil bulk density

Soil Chemical Properties

Soil pH

Soil organic carbon (OC)

Total N (TN)

Available P

Soil Organic Matter

Electrical Conductivity

Causes of Soil Erosion

Severity of Soil Erosion

Consequences of soil erosion

Impacts of Soil Erosion

Soil Erosion Impacts on soil quality

Soil Erosion Impacts on Changes in land productivity

Soil Erosion Impacts on Yields of cultivatable crops

Implications of Soil Erosion on Food Security

Conclusion

Recommendation

Declarations

Conflict of Interests

Acknowledgements

References

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