1. Introduction
According to current studies, more than half of the world’s agricultural fields will be salt-affected by 2050 [1,2]. Soil salinization affects 19 million hectares of land in Sub-Saharan Africa [3]. Ethiopia is first in Africa in terms of the size of saline-affected soils caused by both human activity and natural sources, and seventh in the globe in terms of the proportion of total land area impacted by salinity [4].
There are over 12 million hectares of arable land in Ethiopia [5]. Even if the potential and actual irrigated area are not well understood [6,7], estimates of Ethiopia’s irrigable land range from 5.3 to 7.5 million hectares [8], with an average of 6.4 million ha. Around 11,000 acres of Ethiopia’s total land area are thought to be affected by salinity and sodicity. According to predictions, this will make up 13% of the nation’s irrigated land and 9% of the nation’s total landmass [9].
Every year, salinity and sodicity render a sizable portion of Ethiopia’s lowlands unusable. According to [10], salinity and alkalinity issues are more prevalent in Ethiopia’s 75 million hectares (66 percent of the country’s total area) of arid and semiarid dryland zones. Contrarily, the majority of the country’s export crops, including cotton, sugarcane, citrus fruits, bananas, and vegetables, are grown in the dryland regions.
Poor-quality water, combined with extensive coverage of soils for irrigated agriculture, insufficient on-farm water management techniques, and a lack of effective drainage systems, are all contributing to Ethiopia’s soil salinity problems [11]. According to [12], as large-scale irrigation projects have grown, soil salinity issues have become more severe and have spread quickly, causing crops to completely fail due to a lack of adequate drainage systems for salt control. Salinity issues have long been recognized, and they are becoming more and more severe at worrisome rates [13].
Bioremediation approaches, such as cultivating halophytic forages in high saline areas where traditional field crop development is hampered, may be used to reclaim these soils. Despite these facts, the country is unable to not only reclaim the damaged soil but also cultivate the previously productive land due to economic difficulties. As a result, studies into arid regions and soils affected by salinity are crucial for modern agricultural management, especially in developing countries such as Ethiopia, where agriculture is the primary source of food and income [6].
In Ethiopia, the regions between Ziway and Shala, the Abaya and Chamo lakes, the southern Rift Valley, and the basins of the Awash and Omo Rivers have the most salinity-affected soils. The majority of Ethiopia’s salinity-affected soils are found in the lowlands of Afar, Somalia, and parts of Oromia, Amhara, Tigray, and the southern regional states [13].
Despite the fact that salinity primarily affects dryland, a review of studies on arid lands and soils affected by salinity has emerged as a major concern for modern agricultural management, particularly in developing countries such as Ethiopia, where agriculture is the basis of the economy and arid and semi-arid climatic zones make up more than 60% of the total land area [14].
Nonetheless, regarding the prevalent problem of soil and irrigation water salinity in Ethiopia and its influence on agricultural production, systematically collected, reviewed, and documented scientific evidence is lacking. As a result, gathering and disseminating data on salinity concerns in salt-affected regions is vital for the planning and management of these areas. Furthermore, proper agricultural field management and boosting agricultural production and productivity require knowledge of soil salinity/sodicity and irrigation water quality status. Information regarding the state of soil and irrigation water salinity and its implications for agriculture is an essential topic, particularly in Ethiopia where the expansion of irrigation is considered a key strategic pillar to boost agricultural production and alleviate poverty. Thus, the aim of this paper was to collect and systematically review the literature on salinity problems facing Ethiopian agriculture in particular and soil and water in general, and communicate to the wider society the extent of the problem and its effects, as well as lessons to be learned from past practices.
2. Study Area
This research was carried out in Ethiopia, which is in the eastern part of Africa between 3°00′ and 15°00′ N and 32°00′ and 48°00′ E. (Figure 1). Ethiopia has a tropical climate with highly variable rainfall over both space and time. The highland regions receive about 1200 mm of rainfall annually with little to no temperature variation, compared to less than 500 mm in the lowland regions with significantly greater temperature variation [15]. Areas in Ethiopia that are more than 1500 m above sea level are known as the highlands. The highlands are divided into northwestern and southeastern portions by the Ethiopian Valley Rift system [16].
2.1. Methodological Approach Followed
The review mostly analyzed locally produced original research publications. Each reference used in the paper was looked up and located using several electronic databases, including Web of Science, Google Scholar, AGRIS, Research Gate, Science Direct, Springer, various African and Ethiopian Journals, and the libraries of the Ethiopian research institutes. Additionally, the pertinent data from the Food and Agriculture Organization (FAO) Corporate Statistical Database (FAOSTAT) and the Central Statistical Agency of Ethiopia were utilized.
The severity and effects of salinity on agriculture and agricultural communities are reviewed in studies that rely on both laboratory findings and farmers’ opinions. In order to address the ramifications of the salinity issues on agriculture from many angles, the study created more logical conclusions than actual data. As a result, the reader will see more facts than conclusions, outcomes in tables and figures than conclusions, and causes than consequences in this essay. This comprehensive literature review classifies the salinity and sodicity level of the soil and irrigation water in Ethiopia using fundamental standards and offers practical solutions to issues brought on by salinity.
2.2. Why Salinity Frequently Occurs in Dryland Areas of Ethiopia
According to various studies, salinity is more prevalent in dryland areas [17], which is also true in Ethiopia. As a result, this section delves into the realities of why this is happening. Salinity will accumulate as groundwater rises to the surface of the ground in dryland areas due to water imbalance, which means significant evaporation and a lack of rainfall to drain down; as a result, soil salinity will increase. Groundwater levels rise when the rate of outflow is less than the rate of recharging. In Ethiopia, saline soils occur naturally when water tables are close to or adjacent to the soil surface. In [18], it was found that soil salinity was induced by poor soil conditions and insufficient irrigation systems at the Fursa River diversion irrigation project (in Ada’a woreda of Afar Regional State, Northeast Ethiopia).
Rainwater can be stored as soil moisture, percolated, or combined with groundwater after it enters the soil. When groundwater levels are extremely low, it rises in the form of capillaries, which transport soluble salts to the surface of the soil and leave them there. As a result, salt builds up in the soil pores, clogging them and causing a salinity problem. Furthermore, the impacts of irrigation on soil salinity and crop productivity in the Gergera watershed (in Atsbi-Wonberta, Tigray, Northern Ethiopia) have generated an increasing threat of soil sodification due to the use of low-quality surface water for irrigation, according to [19].
The underlying profile of Ethiopia’s Central Rift Valley soils is naturally sodic, and irrigation with low-quality groundwater has aggravated salt development [13]. Groundwater rises at the top surface in low-lying areas or the break of slopes or runs directly into streams. In all of these situations, it may transmit dissolved salt from the underlying soil and bedrock. As a result, dryland salinity can develop as a result of a lack of vegetation, as well as crop and grassland growth that reaches the groundwater system at varying depths. Additionally, soil salinization and waterlogging are recorded by [19] when groundwater approaches close (5 m) to the topsoil due to capillary rise. Slope variations in the water level in streams, lakes, and dams can also cause additional saline groundwater to flow into these surface water resources due to groundwater.
Water exceeds the root zone’s storage capacity in regions where recharge is high, and the water percolates beyond the root zone and joins the groundwater, extending the discharge area. The majority of groundwater movement occurs adjacent to and downslope, and it flows through a shallow, porous layer. As the groundwater reaches the discharge point, the dissolved salts in the soil are transferred to it. When groundwater rises to the surface of the soil, it forms a seep. As a result, as water evaporates from the seepage zone, salts are left on the soil surface. In [20], a study was conducted in the thickly forested Gerjalle district of northern Ethiopia to corroborate this claim. However, the area has no swampy indication; instead, it has a water deficit.
The water table began to rise as a result of the farmers’ clearing and destruction of the dense forest, according to the community. This suggests that native woodland trees were previously responsible for maintaining a shallow water table and a healthy salinity balance [20]. As a result, deforestation in Ethiopia’s dry areas is another likely reason for rising water tables and salinity build-up.
Flood-based irrigation systems, also known as spate irrigation, were pioneered by Ethiopian farmers in dryland locations. Spate irrigation is beneficial in mountain catchment lowlands, where farmers can benefit from short-term floods. When the water arrives early in the cropping season or late in the cropping season, crop productivity suffers dramatically. Because floods as a source of irrigation are difficult to rely on [21]. Van et al., 2011 [22] recognized the following problems with the method after studying spate irrigation in the Tigray region: (1) flood flow is not evenly distributed between upstream and downstream users; (2) technical flaws in the development of local diversion canals cause river course changes; (3) improper secondary and tertiary canals cause infield scour and the formation of gullies in the fields, reducing available soil moisture.
3. Severity of Soil Salinity in Agriculturally Potential Areas of Ethiopia
The authors of [23] investigated the status of soil salinity in the country’s northeastern region (coded as sites one, two, and three). They discovered that EC ranged from non-saline to moderately saline (0.831 to 7.52 dS/m) in the upper soil depth (0 to 50) and (0.482 and 5.08 dS/m) on the subsequent subsurface layer (50 to 200 cm soil depth) at site one, and non-sites.
The cation exchange capacity (CEC) of site one was high at the soil surface (31.58 cmol (+)/kg soil) and low at the sub-surface layers (7.24 to 45.4 cmol (+)/kg soil). At location two, the surface concentrations were extremely high (71.1 to 73.1 cmol/kg soil). At site three, the CEC was medium to high (24.76, 40.38, 37.18 cmol (+)/kg soil) from the surface to subsurface. In sites one and two, the exchangeable sodium percentage (ESP) ranges from low to medium (0.8 to 2.3 percent, 1.5 to 2.1 percent, respectively). The percentage of salt that can be exchanged varies from low to medium (1.5 to 2.1 percent). In the middle layer (40.1%) of site three, ESP is extremely high [23].
The pH of the soil in the area ranged from 7.7 to 8.3, indicating that it was moderately to severely alkaline, according to a comparable study in the area [23]. In general, the soil in the area is extremely salinized, and it nourishes a population that is extremely sensitive to food poverty. As a result, all stakeholders and interested parties are encouraged to work on soil reclamation in the area as a result of this review study.
The pH of the surface soil ranged from 8.01 to 8.47 in research conducted in the northern portion of the country by [24], with pH values of soil profiles moderately increasing with increasing depth. As a result, the soil in the area was alkaline, posing a threat to nutrient availability. The relative quantity of alkaline-producing cations is the principal driver of this soil characteristic.
In irrigated soils in Ethiopia’s Middle Awash River basin, in the country’s northeastern region, [25] discovered elevated EC concentrations. The order of magnitude of soil exchangeable cations in the area is Ca > Mg > Na > K. The dominance of exchangeable Ca and Mg contents indicates that the soil parent material is primarily rich in basic cations and that the soil colloidal particles, due to their higher selectivity coefficient over monovalent cations, retain the divalent cations in higher concentrations for longer periods [26]. With a range of 44.06 to 61.76 cmol (+)/kg, the CEC was found to be 44.06 to 61.76 cmol (+)/kg. The percent base saturation (PBS) of the soil in the study area varied greatly. The sodium adsorption ratio (SAR) of the soil solution ranged from 0.39 to 6.72 for surface soils in the area. When considering agricultural uses, the EC values calculated from soil profiles in the area were generally below the threshold level to qualify for the saline-affected soil classes [24].
In Ethiopia’s northwestern region, [27] evaluated the salinity and sodicity dangers of soil and irrigation water. According to United Soil Salinity Laboratory Staff (USSLS) [28], the soils irrigated by the Shewa Robit River met the requirements for being classed as saline soils because the EC was greater than 4 dS/m and the exchangeable sodium percentage (ESP) was less than 15%. Nonetheless, soils watered by a mixture of Shewa Robit River and groundwater sources were classified as saline–sodic soils using the same criterion because the EC was greater than 4 dS/m and the ESP was greater than 15%.
According to [21], the soils of the Melka Sedi-Amibara Plain in the Middle Awash Valley, northeastern Ethiopia are extremely saline, with EC ranging from 16 to 18 dSm−1. Soluble Na+, Ca2+, Cl−, and SO42− are the key soluble salinity constituents seen throughout the profile. The authors of [29] found that soil irrigated with groundwater in the Bora district of central Ethiopia had a higher pH (greater than 8) than soil irrigated with the Awash and Modjo Rivers. This, in addition to the rivers, is a result of the area’s high saline groundwater supplies.
According to [30], the PH of the soil increased as it progressed down the soil profile. As a result, the soil PH in the Ziway region was somewhat alkaline at the surface (7.90) and gradually went down the profile to alkaline, reaching 9.57 in the subsurface layers. According to [31], the surface and sub-surface soils in the Meki Ogolcha area of central Ethiopia, which were irrigated using Lake Ziway and groundwater, were determined to be saline–sodic and sodic soils. Similarly, the ESP of the soil profile opened increased from 9.03 at the surface of 0–28 cm to 19.56 at a depth of 166–200 cm at the Ehio-Flora farm at Meki Ziway [32].
The EC of the soil at Meki Ogolcha land flooded from the Meki River ranges from 4.38 dS m−1 in the upper horizon to 11.58 dS m−1 in the lower horizon, showing that the soils are salinized, according to [31]. The effect of soil salinity and sodicity levels on the saturated soil hydraulic conductivity of the surface layer was classified as moderate permeability in the same study, whereas layers 2 and 3 of the same profile were classified as slow permeable. The authors of [33] conducted research in the Wonji irrigation zone and discovered that in some areas of the sugar estate, improper irrigation practices result in a shallow groundwater table, potentially generating salt concentrations.
The authors of [34] looked into the groundwater table and salinity conditions at Metehara Sugar Estate in central Ethiopia and discovered that the estate is suffering the effects of rising groundwater table (GWT) and salinity in some fields, resulting in decreased yields and the obstruction of a wide area of cultivable land. According to the same source, the severity of soil salinity rose as GWT increased. The bulk of the plantation area has a moderate to severe soil salinity problem, with the capillary rise (secondary salinization) from saline groundwater increasing soil salinization in the subsoil (40 to 100 cm) [34].
The soil pH in the Kesem area of central Ethiopia ranges from 7.7 to 10.3, which is alkaline, according to [35]. The soil pH in Melka Sedi and Melka Werer farm areas in central Ethiopia ranges from 6.9 to 8.9, according to [36]. According to the authors, the pH in sodic and saline–sodic soils, where sodium appears to be dominant, is high.
The pH in the Amibara area is generally higher than 7, indicating an alkalinity reaction. The pH ranges in salinity-affected soils fluctuate because the presence and concentration of cations influence the pH value or soil reactivity. Previously, [37] discovered a similar result in Amibara. According to [38], the pH value of the Allaideghe plains in the Amibara district was continuously high, ranging from 7.7 to 8.2.
Habtamu et al., 2016 [39] claims that the soils in the Kesem area have a high EC, implying a high occurrence of sodicity, with values ranging from 0.9 to 8.0 dS m−1 and 9.9 to 42.7 percent, respectively. Based on a field investigation, [40] discovered around 40, 16.98, and 0.02 percent saline, saline–sodic, and sodic soils, respectively, over 4000 hectares of irrigated lands near Melka Sedi.
The EC in the Amibara irrigation field ranges from 0.41 to 93.94 dS m−1, according to [37]. In the Amibara Irrigation region, salt soils make up about 27.51 percent of Fluvisols and 8.76 percent of Vertisols, according to the study. 6.36 percent of the Fluvisols in the area are saline–sodic soils. According to the same study, sodic soils make up 0.33 percent of Fluvisols in the Amibara Irrigation field, and a major number of farms beneath the light-textured Fluvisols have salinity and sodicity problems.
The pH of the surface soil of a Tendaho sugarcane-producing farm ranged from 7.8 to 8.6, indicating that it was moderately alkaline to strongly alkaline, according to [41]. The electrical conductivity (EC) of the soils was higher than 4 dS/m in most of the profiles opened in the Tendaho sugar plantation farm, indicating that there would be an actual salinity hazard in the area’s soils, and high EC values were recorded in the profile’s middle layer, due to salinity leaching from the surface to the subsurface layer. According to the same authors, the ESP of the profile opened at the farm’s lowest point ranged from 4.93% at the surface to 28.96% at a subsurface depth of 30 to 80 cm, and the soils represented by this profile were prone to sodicity dangers.
Salinity-affected soils dominate around 80% of the Dubti/Tendaho state farm, according to another source [4], which constitutes 27.14 percent saline, 29.22 percent saline–sodic, and 23.36 percent sodic soils. According to the same authors, salinity-affected soils comprise roughly 82 percent of the Dubti/Tendaho state farm, as predicted by Kriging (29.0 percent saline, 30.63 percent saline–sodic, and 22.54 percent sodic soils). Finally, according to the authors, shallow (less than 2 m) groundwater with poor water quality due to high salt occupied more than half of the Dubti/Tendaho state farm. He said, in general, that the rate of expansion of salinity-affected soils had accelerated through time and space. In general, the findings revealed that the salinity of the soils in the area is unavoidably saline, ranging from mild to severe. When these salty soils are correlated with agricultural productivity in the same region, it is easy to see how salinity is decreasing agricultural productivity by diminishing soil and water fertility.
4. Severity of Irrigation Water Salinity in Ethiopia
All irrigation waters include varying degrees of dissolved salts and other components (Table 1). When dissolved elements are present in small to moderate concentrations, they can help crops thrive, but when they are present in excessive quantities, they can degrade soils and impede plant growth [23]. Many researchers have looked into how irrigation water quality affects soil quality over time [42]. Water quality difficulties in irrigated agriculture include salinity, sodicity, specific ion toxicity, decreased infiltration rate, and hydraulic conductivity [43]. According to physical observations and publicly available information, soluble salts have accumulated in the soils of recently created small-scale irrigation systems and groundwater sources in Tigray [40].
The authors of [24] assessed irrigation water in the Tumuga and Gerjale districts of Ethiopia’s Tigray region. Thus, the ECw at Tumuga ranged from 0.13 to 0.34 dSm−1, while it ranged from 0.07 to 0.37 dSm−1 in Gerjale. Similarly, irrigation water quality in the same locations is classified as low to medium salinity [28,44].
According to [24], Mg2+ was the most prevalent cation at the Tumuga site, followed by Ca2+, Na+, and K+. Ca2+ was the most abundant cation in the Gerjale site, followed by Mg2+, Na+, and K+. HCO3− was the most prevalent anion at both sites, followed by Cl−, CO3−2, and SO4−2. However, according to USSLS, the boron concentration was below the standard set for the toxicity level of sensitive crops at both sites (1954). SAR ranged from 0.19 to 4.95 at Tumuga and 0.25 to 3.28 at Gerjale in the same study by [24] with Ca+2 and Mg+2 concentrations greater than Na+ concentrations at both sites. Furthermore, at Tumuga, total dissolved salt (TDS) levels in irrigation water range from 674.17 to 1215.41 mg L−1, whereas at Gerjale, TDS levels range from 408.21 to 1204.87 mg L−1. The concentrations of TDS were classed as mild to moderate in their potential concern based on the degree of restriction placed by [45] on the use of water for irrigation. As a result, if correct management is not implemented, irrigation water will pose a significant salinity problem in the area. Similar to these findings [46] classified the area’s irrigation water quality as mild to moderate with a significant potential irrigation concern.
Similarly, [23] studied irrigation water salinity in the country’s northeastern regions (mainly Awash Valley), selecting three sites based on the SAR, pH, and EC of water collected from the Fursa River and discovered a SAR of 20.40. Nonetheless, water with a SAR value of more than nine (>9) was strictly prohibited from being used for irrigation due to the risk of salinity poisoning [42]. In addition, the Fursa River’s pH is somewhat saline, according to the same study (7.36). According to several types of research, the levels of EC are classed as medium (1.31 EC (dSm−1) [43]. Furthermore, the total dissolved solids were found to be in the slight to medium range.
According to the findings, sodicity values and the combined effect of salinity and sodicity levels in the area are over the FAO criteria for water quality limitation limits. There are signs of sodicity development potential not just in the soil, but also in the irrigation water. As a result, the findings underline the importance of selecting salinity-tolerant crops and proper water management through appropriate irrigation technologies to maintain soil productivity in the proposed irrigation system.
The author of [27] examined salinity and sodicity hazards in Ethiopia’s northern regions and found that the pH of irrigation water from the Shewa Robit River and groundwater sources ranged from 8 (moderately alkaline) for Shewa Robit River water to 8.9 (strongly alkaline) for groundwater. The reflections of considerably larger quantities of bicarbonates in the water are reflected in this feature of the PH, which influences crop yields.
Ca2+ was the most abundant dissolved cation, followed by Mg2+, while Cl− was the most abundant anion, followed by HCO3−, in both the Shewa Robit River and groundwater sources. Similarly, according to the US Salinity Laboratory Staff [28] sodicity hazard guidelines, both the Shewa Robit River and groundwater sources have minimal sodicity dangers for irrigation [27].
Farmers in the Bora district use groundwater for irrigation, according to [29], and the water had a pH > 8.5, EC 4 dS/m, and ESP > 31. As a result, according to the FAO’s definition of salinity, irrigation water is classified as sodic. Bora district is located in Ethiopia’s rift valley, where soil sodicity is a major issue due to increased evapotranspiration [47].
According to [48], the pH of irrigation water and factory-utilized water at Wonji/Shoa Sugar Plantation ranged from 7.4 to 8.1 (above neutral), whereas drainage water pH ranged from 7.0 to 7.8 and all groundwater pH ranged from 7.1 to 8.3. According to the author, the total salinity content of groundwater in some sugarcane fields is relatively high (EC > 700 S/cm). This is the upper limit at which osmotic effects can occur. According to the same source, the SAR to EC ratio shows that the infiltration rate can potentially be reduced. The ECw of groundwater around the Wonji sugarcane plantation is moderately severe, and Beseka Lake is highly severely saline, according to [34]. The SAR for the Awash River, Irrigation Canals and Reservoirs, and drainage water in the same area range from low to very toxic for factory waste, groundwater, and Beseka Lake.
Water samples from some surface fields and main irrigation canals surrounding Kesem exhibited a high pH (>8) according to a study by [35], due to the dominance of bicarbonate ions in the area. The EC values in all water samples are extremely high when compared to the critical value, leading to the conclusion that groundwater salinity (EC) might severely influence crop water needs. Sodium is the most abundant cation in all water samples in the Kesem area, followed by calcium and magnesium, while bicarbonate and chloride ions are the most abundant anions.
The concentration of salinity in all groundwater samples was too high to affect plant growth from a toxicity standpoint. Chloride ion toxicity was also relatively high in all groundwater samples. In general, all water samples were of poor quality in terms of salinity and sodicity effects. Water flowing internally from the upland area (perhaps from Mount-Fentale), dissolving saline rocks, and seeping to low-lying portions of Kesem is one suspected source of groundwater that is currently inundating several cropped areas in Kesem.
Most water samples taken from middle Awash had total dissolved solids (TDS) ranging from 100.0 to 40,737 mg/L, according to [49]. According to the author, the analyzer water sample’s high quantities of soluble carbonates, bicarbonates, chlorides, sulfates, phosphates, nitrates, iron, manganese, and other minerals were to blame for the elevated TDS value. The author also mentioned that deep wells with high electrical conductivity values between 2.36 and 2.44 dS/m were common. Wells were discovered to have high pHw values, which may be related to the presence of bicarbonate and carbonate sources from subsurface weathering of calcite minerals. The pH in various Awash River water test sites varied similarly from 8.4 to 8.58, which was thought to be close to the typical pHw range of 6.5 to 8.4 for particular crops, according to the same author. However, there are considerable amounts of soluble salt in deep wells and drainage waters.
Furthermore, soluble Na levels in deep wells and drainage waters ranged from 71.8 to 500 mg/L and 75.33 to 1150 mg/L, respectively. Water with high Na levels can be hazardous, when soluble sodium levels in irrigation water exceed 120 mg/L [49]. According to [23], the pH of the water in the Fursa River is slightly alkaline (7.36) or nearly neutral. Additionally, they found that the electrical conductivity (ECw) of the irrigation water is in the medium range. Additionally, the total dissolved solids range from low to considerable. Due to sodium’s effects on the soil, irrigation water with high salinities is particularly problematic and constitutes a sodium danger, which is typically quantified in terms of sodium adsorption ratio (SAR). According to [23], the SAR of the water used as an irrigation source for the Fursa irrigation system is 10.0, whereas the corrected SAR is 20.40. However, water with a SAR value of more than nine (>9) is not recommended to be used for irrigation due to the risk of sodium poisoning [43]. This entails early notification of a potential sodic soil hazard in the area [23].
The author of [4] reports that the irrigation water quality of the Awash River in the Dubti/Tendaho region was found to be severely problematic in the summer and autumn but mild and safe in the winter and spring. The same source claims that the pH of irrigation water varied from 7.78 to 8.72 on average, with spring and fall having the lowest and highest values, respectively. The pH of the water sample taken at the Dubti/Tendaho state farm during the autumn was higher than average (>8.4), according to the author. The cause for this could be the addition of waste effluents with high alkaline contents from the upper Awash basin stream through erosion in the summer, and the lingering effects of those waste materials in the autumn when the dilution effect is less noticeable.
Furthermore, the EC of River Awash water at Dubti/Tendaho state farm sites is questionable in the autumn and summer (750–2250 Scm−1), but good in the winter and spring (250–750 Scm−1). The seasonal change, according to the author, could be attributed to excessive evaporation in the summer and autumn. According to [4], the irrigation water quality near Dubti/Tendaho state farm was exceptional (less than 10 SAR) in all seasons except summer, which was in the good range (10–18 SAR).
Based on a tighter evaluation of irrigation water quality in terms of SAR value provided by [40], the author asserts that the Awash River water used in the area of Dubti/Tendaho falls within the range of (>5 SAR) in the autumn and summer and significantly (2–4 SAR) in the winter and spring seasons. The findings in [41] were similar. The same author claims that the salinity of irrigation water is particularly important because of salt’s effects on the land and because it poses a sodium threat that is frequently expressed in terms of SAR.
In general, the reviewed findings confirmed the severe condition of irrigation water salinity in the country. Ethiopia is among the low-income countries in which the economy is extremely vulnerable. Irrigation development is capital investment intensive. Therefore, unless this observed ongoing salinity problem is tackled on time and appropriate irrigation practices are adopted, the country could face irreparable economic failure. Not only an economic failure but also environmental degradation causing severe food insecurity around arid and semi-arid dryland areas of the country.
5. Salinity Effects on Crops at Different Growth Stages
Even though most crop plants are prone to salinity generated by high salinity concentrations in the soil, salinity is one of the most severe ecological variables limiting agricultural performance [50]. It has a significant impact on crop quality and yield. These saline effects on many crops are cumulative consequences posed at several growth phases. Crops in Ethiopia’s semi-arid and arid lowlands and valleys are being harmed by salinity and alkalinity [51]. According to [52], the most tolerant crops can withstand a salinity concentration of saturation extract up to 10 gL−1, the fairly tolerant crops up to 5 gL−1, and the responsive crops up to 2.5 gL−1. Despite this, most crops are unable to thrive beyond these limits. Enhancing salinity tolerance in cultivated plant species is an important strategy to take advantage of the large area of saline soils and saline water sources. This is conceivable if the influence of various amounts of salinity on crops at various stages of development is well known.
5.1. Effects of Salinity on Vigor, and Relative Water Content of Selected Crops
The most useful measures for assessing crop plants’ salt tolerance are germination and seedling growth indices [53]. Salinity, on the other hand, has an impact on early survival, seedling emergence, and seed germination [54]. Salinity affects physiological growth and has acoustic effects on crops due to osmotic embarrassment and ionic toxicity [55].
Furthermore, in [56], two haricot bean cultivars (Lehade and Chercher) were examined at five different salinity levels (0, 2, 4, 8, and 16 mM). It was found that the seedling and root vigor indices, shoot phytotoxicity, and relative water content of the shoot and root varied significantly between cultivars under the various salinity pressures.
The Lehade cultivar has greater seedling, shoot, and root vigor indices than the Chercher cultivar. In comparison to the Chercher cultivar, the Lehade cultivar exhibits higher seedling, shoot, and root vigor indices. This was due to the fact that Chercher recorded 91.5 percent germination while Lehade claimed 100% germination.
Lehade showed a similar germination % to controls in all circumstances, although having shorter root and shoot lengths [56]. A crop variety may sprout well under salinity stress. Salinity, on the other hand, may stifle the growth of its seedlings [57]. Similarly, numerous cultivars showed the highest initial germination % even at high salinity (16 dS/m), but their vigor declined as seedling growth parameters advanced [58,59].
Cultivar Chercher had a good seedling tolerance index and minimal phytotoxicity in the shoots and roots. Shoot phytotoxicity differed greatly between cultivars, with Lehade having the highest and Chercher having the lowest. In terms of root phytotoxicity, however, there was no significant variation across cultivars. Chercher, on the other hand, had relatively low root phytotoxicity, indicating that it tolerated higher NaCl concentrations better than Lehade. This reveals that there is genetic heterogeneity in NaCl tolerance and phytotoxicity effects amongst cultivars. [60] discovered genetic diversity in salinity tolerance in haricot bean and chickpea cultivars.
Further, the study discovered statistically significant variations between Lehade and Chercher’s relative water contents for the shoot and root. When compared to Lehade, Chercher has the highest relative shoot and root water content. According to [61], cultivars with the largest relative water content in the seedling are more resilient to the negative effects of dilution-induced salinity. Increased salinity, according to [56], significantly reduced the vigor indices of seedlings, shoots, and roots. According to this study, salinity reduces haricot bean vigor indices because bean seedlings cannot adjust osmotically to the toxic effects of Cl− and/or Na+. The lowest vigor indices were found at 16mM NaCl concentration, where they were 39.9%, 29%, and 11% for seedling, shoot, and root, respectively.
5.2. Phytotoxicity of Salinity on Shoot, Root, and Seedling Relative Water Content
The phytotoxicity of the shoot and root increased as the salt concentration rose [56]. This study discovered the highest levels of phytotoxicity in the shoot (57.04%) and root (58.74%) at 16 mM doses. The authors of [62] assert that wheat’s root and shoot phytotoxicity increased at greater concentrations and decreased at lower quantities. Increasing the amount of NaCl has a salinity inhibitory or toxic effect, which is typically noticed as soon as the radicle starts to elongate [63].
The seedling tolerance index significantly decreased when the NaCl level rose [56]. The haricot bean has a low tolerance for NaCl concentrations, especially at 8 mM and 16 mM, according to a study by [56]. Low tolerance to NaCl may be caused by physiological changes that occur during haricot bean seed germination and seedling growth. Some haricot bean and sorghum cultivar seedlings have a low tolerance to salt levels of 16 dS/m, according to research by other authors [60,64].
According to [56], the relative water content of seedling shoots and roots decreased as salinity concentration increased. Relative root water content was shown to have a strong negative connection with the rise in salinity (y = −0.764x + 53.51; R2 = 0.904). The relative water content of the root and shoot of haricot bean seedlings decreased with rising NaCl concentrations. As salinity rose, the relative water content of the shoot and roots decreased, going from 52.63 to 40.01% and 49.67 to 37.26%, respectively. The shoot and root’s lowest relative water content was found at a salinity concentration of 16 mM [56]. The author of [60] discovered that the relative water content of seedling shoots and roots significantly decreased when salinity levels increased.
5.3. Effects of Salinity on Seed Germination and Early Growth Stages
Significant reductions in germination percentage, rate, root and shoot length, and fresh root and shoot weights were seen with increased salinity [65]. It is rational to expect that enhancing crop salt tolerance will be a significant component of plant breeding in the future if global food production is to be sustained [66] given the projected growth in global food production over the next few decades. Germination and seedling traits are the most practical factors for choosing salinity-tolerant crops [67].
Salinity tolerance at the two early growth stages and the levels of salinity tolerance varied greatly among genotypes, according to research on the effects of salinity on seed germination and early vegetative growth of nine barley genotypes (five landraces and four breeding lines) at four salinity concentrations (0, 100, 150, and 200 mM) and four seawater concentrations (0, 20, 30, and 40%) [68]. The percentages of reduction for all variables in all genotypes rise with rising saline concentrations.
Despite the fact that reduction percentages differ from genotype to genotype, an experiment in seawater (saline water) demonstrates that all of the variables under consideration, such as the reduction percentage of germination, emergence, radicle length, and dry weight of roots and shoots, decline with increasing salinity concentrations [68]. The germination stage is the developmental stage that is most impacted by salt stress, according to [54,69].
The authors of [70] examined the responses of 20 lowland sorghum (Sorghum bicolor L. Moench) accessions to salinity stress during seedling growth at salinity values of 0, 2, 4, 8, and 16 dS/m. The factors assessed were final germination percentage, germination rate, seedling shoot length, and seedling root length under various salinity stresses. There are significant salinity stressors for the majority of accessions at 16 dS/m for ultimate germination %, 8 and 16 dS/m for germination rate, 8 and 16 dS/m for seedling shoot length, and 16 dS/m for seedling root length. A high saline environment slows germination (increased days of emergence). The study concluded that the salinity stresses influenced the evaluated variables; however, the effects are variable, and the stress increases as salinity levels rise, indicating that all accessions responded similarly to salinity stress in terms of the above parameters [70]. Rice [71] and cowpea [71] have both had similar investigations.
The author of [60] studied the effects of salinity on 14 haricot bean (Phaseolus vulgaris) cultivars during germination and seedling growth at salinity values of 0, 2, 4, 8, and 16 dS/m. The end germination percentage, seedling shoot-to-root ratio, seedling root length, and seedling length were the criteria that were assessed. Salinity had a greater impact on seedling root length than on shoot length and variety. Awash Melka was shown to be salt-tolerant both during germination and seedling development.
Seedling Root Length was more affected by salinity than Seedling Shoot Length in the fourteen haricot bean varieties that were examined. The rate of seedling mortality rose together with the salt levels. The effect of salinity on different haricot bean varieties grew more obvious as the salinity level rose as the growth stage advanced. The Roba-1, Red kidney, Tabor, and Zebra cultivars were salt sensitive throughout seedling development. Mexican 142 was susceptible to salinity while it was a seedling, but as it matured, it became tolerant to it. On the other hand, the variety Dimtu was susceptible to saline during seed germination and seedling development [60]. Crop types are significantly impacted by salinity, albeit the impacts differ based on the location’s salinity levels [72].
Additionally, [73] used tap water as a control group, NaCl and Na2So4 to simulate salt, and 10 seeds of different chickpea landraces from Hagereselam and Samre in Tigray to study the impact of salinity on chickpea (Cicer arietinum L.) germination. They concluded that salinity concentrations have a detrimental effect on the germination and growth of chickpeas. As a result, they found that as salinity concentrations increased, germination, water uptake, and root and shoot length decreased, showing that NaCl has a greater effect than Na2SO4 on chickpea germination and growth. In addition, they discovered that seeds from Hagereselam and Saharti Samre treated with salt absorbed less water than seeds treated with distilled water (0 dS/m salinity level). The ability of seeds to absorb water is influenced by the concentration of salts in both landraces, and the index of reduction increases as the saline level rises from 5 to 15 dS/m [73].
The inhibition index for NaCl for the landrace gathered from Hagereselam varies from about 23% at salinity levels of 5 dS/m to 36.3% at salinity values of 15 dS/m. Na2SO4 treatment on Hagereselam seed, however, causes a 6 to 32% reduction in water uptake compared to the control. The Saharti Samre landrace’s water intake was decreased by 15 to 29% when it was treated with NaCl, and by 5.5 to 26% when it was treated with Na2SO4 [71]. Additionally, 0% germination was seen for high salinity levels (at 15 dS/m) in all landraces and salinity types, indicating a 60 and 80% overall reduction in germination, respectively [73].
Similar to this, according to [74], germination delay is related to the medium’s salinity content and germination is proportional to the amount of water absorbed. Additionally, the type of salinity utilized and the osmotic potential of the medium in which the plant is grown affect the plant’s tolerance to salt. Salinity stress thus inhibited seed germination and postponed seed emergence. A higher saline content lowers the water potential in the medium, preventing growing seeds from absorbing water and limiting germination in addition to the negative effects of certain ions. It is hypothesized that as the water circulation into the seeds decreases during imbibition, the germination rate and final seed germination decrease. As a result of osmotic effects, salinity stress can influence seed germination [74].
Furthermore, [73] discovered that root length decreased as salt levels increased. At 10 dS/m, the landrace from Hagereselam demonstrated the largest loss in root length (82% reduction), whilst the landraces from Hagereselam and Saharti Samre demonstrated the greatest reduction in shoot length (87 and 75% of control, respectively). Chickpea roots and shoots grow very slowly, and the majority of the roots lyse and dry out after a few days as a result of high salinity inhibiting root and shoot elongation by reducing the plant’s water intake. Similar to this, salinity can restrict root development, reducing water uptake and essential mineral sustenance from the soil, according to [75].
Salinity affects safflower roots more adversely than shoots, even though both are negatively harmed, according to [76]. The authors of [73] assert that salinity has a more detrimental effect on chickpea shoot growth than on root growth. This might be explained by the fact that experimental seeds germinate differently: Safflowers germinate epigeally, damaging the root first, whereas chickpeas germinate hypogeal [73].
In comparison to salinity induced by Na2SO4, [73] discovered that chickpea is highly sensitive to salinity induced by NaCl. [77] On the other hand, discovered that bean (Phaseoucus vulgaris L.) is more susceptible to Na2SO4 than to NaCl. This is because different ions have varied effects on different crops [73]. Furthermore, [73] found that NaCl had a stronger influence on shoot length compared to Na2SO4, where no shoot growth was seen at 10 dS/m for the landraces treated with NaCl. Na2SO4 had a stronger effect at high salinity (15 dS/m) for the Saharti Samre landrace.
According to [73], there are two ways that salinity affects germination: either there is enough salinity in the medium to significantly lower the osmotic potential, delaying or preventing the uptake of water necessary for the mobilization of nutrients needed for germination, or the salinity constituents or ions are toxic to the embryo, causing early death or decline.
Salinity slows or prevents the mobilization of reserve nutrients, suspends cell division, and enlarges and injures hypocotyls, all of which hinder bean seedling growth [77]. The authors of [78] likely found that when salinity levels rose, shoot length decreased. The authors of [58] examined the impact of salinity on 20 Sorghum (Sorghum biolor L. Moench) accessions’ seedling biomass production and relative water content at salinity values of 2, 4, 8, and 16 dS/m. Seedling shoot fresh weight, seedling shoot dry weight, seedling root fresh weight, and seedling root dry weight were the variables that were measured. According to [60], seedling root fresh weight decreased at salinity levels of 4 and 8 dS/m in all accessions, but the effect was more pronounced at 8 dS/m, and 6 accessions were the most salinity affected. Seedling shoot fresh weight of 8 sorghum accessions was more salinity affected at these salinity concentrations. At 8 dS/m, the seedling shoot’s dry weight was significantly influenced. The accessions most impacted by salinity were eight (8). All accessions saw a decrease in seedling root dry weight between 4 and 8 dS/m, however, this reduction was more pronounced at the later salinity concentration, and six accessions were more salinity-affected. As the saline level rose, the relative water content of seedling roots and shoots decreased.
6. Management of Soil Salinity and Its Impacts on Agricultural Production
Saline–sodic soil typically does not exhibit severe sodicity indications. However, when sodicity and salinity coexist in the same soil, management of both conditions becomes more challenging. Consequently, complex issues may not necessarily require an easy fix [61]. Two main strategies are frequently used to maintain production in a saline–sodic environment: (1) adapting the environment to the plant; and (2) adapting the plant to the environment. Both strategies can be used separately or together. For better plant response, the first strategy has been used more frequently [62].
Drainage, leaching, chemical additives, and the plant’s bio-remediation suit alter the saline–sodic environment. While the drainage and leaching methods are challenging and costly. Additionally, unless it is not practical, leaching without subsurface drainage is only suitable in locations with low soil moisture content and deep groundwater tables [63,64,65]. An additional method to address saline–sodic issues beneath shallow water table locations is the application of chemicals followed by bio-remediation [65].
The use of chemical additives for soil reclamation is not new [66]. Gypsum (CaSO4. 2H2O) is the most popular and reasonably priced amendment for removing too much Na+ from soil exchangeable sites by adding a source of Ca2+ that is readily available [67,68,69]. Ca2+ replaces Na+ on the exchange site in the form of leachable Na2SO4 because it has a greater charge than Na+. This Na2SO4 form is easily eliminated either through upward absorption by halophytic grasses or downward leaching [66,69,70,71]. Replaced Na2SO4 should be absorbed from the root zone using salt-loving halophytic species to prevent resodification in saline–sodic environments.
Many studies have been conducted in Ethiopia’s Amibara, Melka Sedi, and Melka Werner dryland irrigation areas to determine how to recover saline–sodic soil utilizing either gypsum with leaching or just halophytic species [72,73,74]. In recent decades, halophytic species have been used in combination with chemical techniques to successfully reclaim saline–sodic soil in numerous countries, including Egypt and Pakistan, but not in Ethiopia. Gypsum and halophytic species are used together, which not only improves the efficacy of salinity and sodicity reclamation but also shortens the period of reclamation compared to single-used amendments [75].
Additionally, ripping is a technique that can be utilized to help with salt leaching and, ultimately, reclamation if soil compaction is a problem, which is typically a concern in sodic soils [76,77]. Shaygan et al. [78] revealed that saline–sodic land reclamation can be accomplished successfully through soil ripping up to a depth of 15 cm. However, ripping should be supplemented with chemical ameliorates (i.e., Ca2+ supplements), particularly for sodic soils [79], to solidify the newly generated pore structure in order to produce long-term improvement in soil physical conditions, particularly in macro porosity. Additionally, the soil needs to be guarded against re-compaction during irrigation [79].
7. Producers’ Perception and Consequences of Salinity to Rural Socio-Economic Conditions
Salinity is a major challenge to rural livelihoods because it has devastating effects on agricultural productivity. As a result, understanding farmers’ views on salinity and adaptive mechanisms to deal with salinity problems is a good starting point for recommending interventions that can help solve the problem [79]. The salinity problem initially impacts soil fertility, resulting in lower agricultural production, food insecurity, and poverty. Although irrigation has become increasingly important in Ethiopia in responding to the stresses of food security, employment, rural revolution, and poverty reduction, and has emerged as a cure for dependable agricultural development, and, thus, for the country’s inclusive economic development, the salinity problem is reversing the importance of damage [80].
Lee and Senadhira 1998 [80] investigated the effects of salinity on producer livelihoods and socio-economic conditions in the Afar Region of Northeastern Ethiopia, finding that 91.18% of respondents believe salinity is increasing, while 5.88% and 2.94% believe salinity is decreasing in their respective localities. As the authors concluded, the rising trend in salinity indicates that farmers are not attempting to manage salinity to the best of their ability in a variety of ways. They also concluded that the problem could be due to a lack of practical knowledge and technical solutions in the areas, leaving producers with little choice but to live with the salinity problem.
In the same study, [80] asked the producers how they identify salinity on their farmland, and 21.57% of the respondents said white crust, 19.61% said dark brown color, and 43.14% said both white crust and dark brown color were visible on the surface of the farmland. The authors of [81] found that 36% of respondents use white crust on the soil surface as a sign of salinity in their fields, 22% consider the dark brown color of the soil as a sign of salinity, and 42% use both the white crust and dark brown color of the soil as a sign of salinity in their fields.
According to [80], the direct and indirect effects of salinity on producers’ livelihoods include abandoning farmland (29.41%), decreasing farm productivity (52.94%), decreasing household income (8.82%), and increasing food insecurity (29.41%). According to [81], around 93% of households in Raya-Alamata and 98.5% of households in Ziway-Dugda are food insecure at various periods of the year. In the Kewet District, 42% of households are food insecure throughout the year. Food insecurity affects 44.8% of Amibara households and 48.6% of Dubti households at some point throughout the year.
Households lost their producing ability as a result of salinity’s consequences, making them exposed to poverty and food insecurity. As a result, food insecurity affects 61.22% of households in Amibara and 38.78% of households in Dubti, respectively. According to [80], households in saline areas use various coping strategies to cope with food shortages. For example, 79.59% of total food-deficit households use food for work activities as a coping strategy, while 24.49% use donors’ food aid as an additional strategy, 20.41% use food purchase, and 14.29% use mutual support as a coping mechanism. According to [81], 42% of food-insecure households in the selected woreda use “food for job activities,” whereas 13% rely on food-aid programs. The 45% of food-insecure households were left to fend for themselves by engaging in off-farm income-generating activities and even purchasing livestock and other assets.
In terms of productivity loss due to salinity, 44.12% of respondents lost 50% of their productive capacity, while 14% experienced a full loss of production. According to [80], 32.35% and 8% of workers lost 25% and 10% of their output, respectively. Similarly, according to [79], 54.3% of respondents lost 50% of their crop production, followed by 38.8%, 32.5%, and 28.9%. (20.8%). The districts of Amibara (35.8%) and Dubti (25.7%) reported the highest crop productivity losses of 25%. In Amibara, about 15% of respondents said they had lost all of their crop yields. Crop productivity declines in salinity-affected areas, resulting in decreased revenue and livelihood.
On the other side, [81] claimed that producers in the arid districts of Amibara and Dubti are abandoning their fields and fleeing to adjacent cities and towns in search of work, resulting in yet another terrible socio-economic disaster. Another socioeconomic concern are health issues, particularly among women and children; as a result of the extra effort, they do to meet their daily necessities [81]. Furthermore, farmers move their livestock to other locations in search of pasture, where they have frequently stolen their livestock [81]. Farmers in salinity-affected areas believe that salinity is one of the many problems preventing them from selling their crops since it reduces agricultural productivity and quality [81].
8. Conclusions from the Reviewed Findings and Recommendations
According to the review findings, the salinity problem in Ethiopia, both in soil and irrigation water, and its impact on agricultural production is worsening. It can be argued that soil salinity and irrigation water salinity have a substantial relationship. As a result, salt in irrigation water sources results in saline soil, and vice versa. This is a strong indication that irrigation and soil management in the country are not properly managed. It is also discovered that cash crops of export quality and used as a source of foreign currency are grown in salinity-affected areas of the country, implying that salinity is one of the numerous factors contributing to the country’s foreign currency shortfall. It may also be concluded that if the current irrigation system is maintained, it is likely that the majority of currently farmed lands will become unproductive, necessitating systematic farm area management to protect informed knowledge of their level and improve management operations.
One of the simplest methods for recovering and controlling salinity-affected soil is biological, particularly for Ethiopian smallholder farmers who lack the resources necessary to carry out expensive corrective treatments. Smallholder farmers should be educated about biosaline remediation techniques and halophytes plants, especially woody species, to achieve this. Compost application is also one of the more easily accessible salinity restorative techniques that smallholder farmers can use. It is important to carefully assess the capacity of numerous multifunctional tree species to reduce salinity in arid areas, including salinity bush (Atriplex spp.). Additionally, the government and all other parties involved should focus their efforts on indigenous agroforestry systems and practices that are profitable and viable in a variety of salt-affected places. The following activities should be prioritized: technical monitoring of irrigation water sources, selection of suitable varieties and crops based on soil type, salinity and sodicity level, and quality of irrigation water; leaching of excess salts; careful irrigation system and fertilizer application combined with the addition of organic manures; and plowing of lands with organic manures. Equally important is to improve irrigation efficiency through the implementation of effective management practices and appropriate drainage to control groundwater levels in irrigated fields. Furthermore, interdisciplinary parties must be involved to properly reclaim and manage saline soils in Ethiopia’s dry plains.
All authors significantly contributed to the development of this manuscript. N.T. oversaw the conceptualization and review of the original draft. The manuscript was reviewed, edited, and improved by D.Y., A.K. and G.T.A. All authors have read and agreed to the published version of the manuscript.
The study is retrospective; hence, formal consent is not required.
Data can be made available from the corresponding upon request.
Haramaya University and Samara University are sincerely acknowledged for the staff time granted for this review work. Most of the materials and information used were collected from the Ministry of Agriculture. The Ministry is thanked for allowing the material to be accessed. Gebiaw T. Ayele received funding and acknowledges Griffith Graduate Research School, the Australian Rivers Institute and School of Engineering, Griffith University, Queensland, Australia.
The authors declare that they have no conflict of interest.
Footnotes
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Enlarge this image.Figure 1. A map of the study area (Ethiopia and regions) depicting changes in elevation derived from a 30 m digital elevation model (source: DEM; source http://www.worldclim.org/).
Chemical composition of the water used for irrigation at the three sampled sites.
| Water Parameter | Units | Degree of Restriction [ |
Values for Fursa River | Severity Status | ||
|---|---|---|---|---|---|---|
| None | Slight to Moderate | Severe | ||||
| Electrical conductivity (EC) | dS/m | <0.7 | 0.7–3 | >3.00 | 1.31 | Slight to moderate |
| Total dissolved solids |
mg/L | <450 | 450–2000 | >2000 | 838.40 | Slight to moderate |
| Sodium (Na+) | meq/L | 70.00 | Severe | |||
| SAR | meql-1/2 | <3 | 3–9 | >9.00 | 10.00 | Severe |
| Adjusted SAR | 20.40 | |||||
| Calcium (Ca2+) | meq/L | 0 to 800: normal range | 88.80 | Normal | ||
| Magnesium (Mg2+) | meq/L | 0–120: normal range | 8.51 | Normal | ||
| Potassium (K+) | - | - | 30.00 | Normal | ||
Source: [
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; Yadeta, Dame 2 ; Kebede, Asfaw 3 ; Ayele, Gebiaw T 4
1 Department of Water Resources and Irrigation Engineering, Haramaya Institute of Technology, Haramaya University, Dire Dawa P.O. Box 138, Ethiopia
2 Natural Resources Management Department, College of Dry Land Agriculture, Samara University, Samara P.O. Box 132, Ethiopia
3 Haramaya Institute of Technology, Hydraulic and Water Resources Engineering Department, Haramaya University, Dire Dawa P.O. Box 138, Ethiopia
4 Australian Rivers Institute and School of Engineering and Built Environment, Griffith University, Nathan 4111, Australia