Copyright © Journal of the Drylands 2010ISSN 1817-3322

214

JOURNAL OF THE DRYLANDS 3(2): 214-219, 2010

Land Suitability Assessment for Different Irrigation Methods in Korir Watershed,Northern Ethiopia

Kassa Teka1, 2*, Van Rompaey, A.2 and Poesen, J.2

Kassa Teka, Van Rompaey, A. and Poesen, J. 2010. Land Suitability Assessment for Different Irrigation Methods inKorir Watershed, Northern Ethiopia. Journal of the Drylands 3(2): 214-219

In much of Korir watershed the surface irrigation system is a common practice applied for maize, vegetables and fruittrees to meet water needs. There are very few instances of drip irrigation on small farms in the area. The aim of thisresearch was to evaluate and compare land suitability for surface and drip irrigation methods based on the parametricevaluation systems. Suitability maps were generated for surface and drip irrigation methods by means of RemoteSensing Technique and Geographic Information System (GIS). Study results showed that for surface irrigation, thereis no area classified as S1. Only 28.77% and 91.54% of the study area is with in the suitable range for surface and dripirrigation respectively. The mean capability index for surface irrigation was 45.82 (marginally suitable) while for dripirrigation 60.6 (moderately suitable). The results indicate that by applying drip irrigation instead of surface irrigationmethods, 62.77% can be improved from N1 to S3 and 6.19% and 22.58% from S3 and S2 respectively to S1. Thecomparison of the different types of irrigation revealed that the drip irrigation was more effective and efficient thanthe surface irrigation methods.

Key words: Surface, drip, suitability, watershed, irrigation, Korir

1Department of Land Resources Management and Environmental Protection, Mekelle University, P.O.Box 231,Mekelle University2Physical and Regional Geography Research Group, K.U.Leuven, Celestijnenlaan 200E, BE-3001, Leuven, Belgium*Corresponding author: kassateka@yahoo.com, Tel: +251- 0914726677

Received August 10, 2010, Accepted November 25, 2010.

INTRODUCTIONThe environmental situation in Africa, withdeforestation and soil degradation etc., is a veryworrying (Foty, 1993) and irrigated area per capitais declining and irrigated lands now produce 40%of the food supply (Hargreaves and Mekley, 1998).Consequently, the available water resources maynot be able to meet various demands in near futurethat will inevitably result in the irrigation ofadditional lands in order to achieve a sustainableglobal food security. To develop sustainable use;one has to know the limitations and potentials ofthe land. The best uses for land depend on soilcharacteristics and their response to the use such astexture, rooting depth, stoniness, rockiness, organicmatter content, nutrient status, structures, drainageconditions, slope, etc.

Sys et al. (1991) suggested a parametricevaluation system for irrigation methods which wasprimarily based upon physical and chemical soilproperties. These factors influence the landsuitability in an irrigation practice including soilproperties and topography. Hired et al. (1996);Bond (2002) and Briza et al. (2001) applied aparametric system (Sys et al., 1991) to evaluateland suitability for both surface1 and drip2 irrigation

1 With drip or trickle irrigation the water is applied into the soil through asmall sized opening directly on the soil surface or buried in the soil. Byapplying water at a very slow rate, drip irrigation is capable of deliveringwater to the roots of individual plants as often as desired and at arelatively low cost (Sijali, 2001).

in Morocco, while no highly suitable areas werefound in the studied area. The largest part of theagricultural areas was classified as marginallysuitable. However, a large difference betweenapplying the two different evaluations was obtained(Bazzani and Incerti, 2002). The area not suitablefor surface irrigation was 29.22% of total surfaceand 9% with the drip irrigation while the suitablearea was 19% versus 70%.

Land suitability evaluation for surface and dripirrigation conducted (Bienvenue et al. 2003) inSenegal, using the parametric evaluation systemshowed no area classified as highly suitable (S1)for surface irrigation. Only 20.24% of the studyarea proved suitable (S2 7.73%) or slightly suitable(S3 12.51%). Most of the study area (57.66%) wasclassified as unsuitable (N2). For drip (localized)irrigation, a good portion (45.25%) of the area wassuitable (S2) while 25.03% was classified as highlysuitable (S1) and only a small portion was currentlynot suitable (N1, 5.83%) or unsuitable (N2,5.83%). Mbodj et al. (2004) performed a landsuitability evaluation for two types of irrigation,(surface irrigation and drip irrigation) in Tunisiausing the suggested parametric evaluation.According to the results, the drip irrigationsuitability gave more irrigable areas compared to

2 The surface method of irrigation involves applying water over the soilsurface. The water is conveyed over the soil surface and infiltrates intothe soil at a rate determined by the infiltration capacity of the soil (Sijali,2001).

Copyright © Journal of the Drylands 2010ISSN 1817-3322

215

the surface irrigation practice. Dengize (2006) alsocompared different irrigation methods includingsurface and drip irrigation in southern Ankara. Heconcluded that the drip irrigation method increasedthe land suitability by 38% compared to the surfaceirrigation method. A research done in Iran (Albajiet al., 2007) comparing different irrigation methodsbased on the parametric evaluation approachshowed that 21.52% of the studied area was highlysuitable for surface irrigation whereas 77.47% ofthe study area was highly suitable for dripirrigation method. A study of land suitability forirrigation schemes in Eritrea (Tesfai, 2002) showedthat in surface irrigation practice, 16% of the studyarea was highly to moderately suitable (S1and S2),24% was classified as moderately suitable (S2),17% was marginally suitable (S3) and 40% of thearea was decided as unsuitable (N1) for surfaceirrigation. Similar studies in Lali Plain, Irain(Naseri et al., 2009) showed that by applyingsprinkler and drip irrigation methods instead ofsurface irrigation methods, land suitability classesof 10.8% for the area can be improved.

The main objective of this research was toevaluate and compare land suitability for surfaceand drip irrigation methods based on the parametricevaluation systems for Korir watershed, TigrayProvince, Ethiopia.

METHODOLGYThe Study AreaThe study area, Korir watershed, is located inKilte-Awulae’lo woreda3, eastern zone4 of Tigray.The total size of the area is 14.64km2 (1465hectares) and is located where the grid coordinateis at 564141E & 1517446N and 568959E &1519706N. The mean annual rainfall is about 466mm and the maximum and minimum temperaturerange from 23-28°C and from 9 – 14°C,respectively (Wukro National MeteorologicalService Agency Wukro Branch). The area isclassified as Dry Weyna-Degaagro-ecologicalzone. The topographic features of the watershedinclude mountain, cliff escarpments, hills and plain(1500 – 2300 meters above sea level) (SFPT,2003). The dominant tree species of the area isAcacia etbica which, account to more than 90%(SFPT, 2003).

The agricultural area of the watershed is724.5375ha. Annual crops such as Chickpea,Barley, Maize, Sorghum, and fruit trees such asCitrus, Avocado, Guava, Papaya, Olives andMango are the most important crops for theeconomy and subsistence of the families in the areasince most families earn their livelihoods from thecultivation of these crops. Livestock farmingconstitutes a significant financial reserve for the

3District level administrative hierarchy containing many Tabias.

4 A structure consisting of many Woredas largely regarded as a functionaldivision

majority of the farmers. The animals also takeadvantage of the leftovers of crop fields after theharvest. Part of the watershed is shown below(Figure 1).

Figure 1. The watershed in part (own photo)

Data Collection and AnalysisEach land unit was delineated through Aerial PhotoInterpretation (API 1994) at 1:50,000 scales,digitized on screen using ILWIS and Arc view GISsoftware and improved with ground truth. The landunit map was used as a guide in the field survey,soil sampling and, in turn, developing a moredetailed soil map following a re-interpretation offield observation and soil analysis. The main focusof the study was on existing cultivated lands. Theland evaluation was determined based upontopography and soil characteristics. Thetopography characteristics included slope while soilproperties included soil texture, depth, salinity,drainage and carbonate content. Also, soilproperties such as Cation Exchange Capacity(CEC), organic matter (%OM) and pH wereconsidered in terms of soil fertility (Sys et al.,1991). The internal properties of the soil weredescribed by using profile pits. A soil profile pitwas opened in each land unit, four profile pits intotal, and described using soil description guideline(FAO, 1990). Soil classification was made basedon FAO (1998). Extent of erosion was observedfrom extent of gully cut, exposed rock outcrop,sedimentation into the river course and existingvegetation cover. Nine composite soil samplesfrom demarcated horizons of the four profile pitswere taken for soil physico-chemical analysis ofthe following parameters: Soil texture, soil pH,CaCO3, organic carbon (%), salinity or EC (dSm-1),cation exchange capacity (CEC), total nitrogen and,and available phosphorous. These soilcharacteristics were matched with the Interpretationratings for soil chemical characteristics (Table 1)(Hunting 1976).

Copyright © Journal of the Drylands 2010ISSN 1817-3322

216

Table 1. Interpretation ratings for chemical soil characteristics (Hunting, 1976)Very low Low Medium High Very high

EC (dS/m) 0 - 2 2 - 4 4 - 8 8 - 16 > 16CEC (cmol(+)/kg 0 - 3 3 - 7 7 - 15 15 - 30 >30Ntot (g/100g) 0 – 0.1 0.1 – 0.2 0.2 – 0.3 0.3 – 0.4 > 0.4Ctot (g/100g) 0 – 0.6 0.6 – 1.2 1.2 – 3.0 3 – 8.7 > 8.7pH (H2O) 5 - 6 6 - 7 7 - 8 8 - 9 9 - 10

Moderately acid Slightly acid Slightly alkaline Moderately alkaline Strongly alkalineCaCO3 (g/100g) 0 – 0.5 0.5 – 2.0 2.0 – 5.0 5.0 - 15 > 15Pav (g/100g) 0 – 0.4 0.4 – 1.3 1.3 – 2.6 2.6 – 5.3 > 5.3

Suitability Assessment methodTo evaluate the land suitability for surface and dripirrigation, the parametric evaluation system of Syset al., (1991) was applied, using the soilcharacteristics. For determination the average ofsoil texture, salinity and CaCO3 for the upper 150cm of soil surface, the profile was subdivided into6 equal sections and weighting factors 2, 1.5, 1,0.75, 0.5 and 0.25 were used for each section,respectively (Sys et al., 1991). Six parameters wereconsidered which are, slope, drainage properties,electrical conductivity of soil solution, calciumcarbonates status, soil texture and Soil depth. Ratesare assigned to the aforementioned six parametersas per the related tables, thus, a capability index forirrigation (Ci) was developed as shown in theequation below:Ci = A x B100 x C100 x D100 x E100 x F100Where Ci = capability index for irrigation; A = soil texturerating; B = soil depth rating; C = CaCO3 status; D = electro-conductivity rating; E = drainage rating; F = slope rating.Suitability classes are defined considering the value of thecapability index (Table 2).

Table 2– Suitability index for the irrigation capabilityindices (CI) classes (after Sys et al., 1991)Capability Index Class Definition Symbol

>80 I Highly suitable S1

60-80 II Moderately suitable S2

45-60 III Marginally suitable S3

30-45 IV Currently not suitable N1

<30 V Permanently notsuitable

N2

RESULTSSoil type and Land Mapping UnitsIn much of the Korir area, the surface irrigationsystem has been applied for maize, vegetables andfruit trees to meet water needs. There are very fewinstances of drip irrigation on small farms in Korirarea.

The major soil types found in the studywatershed are Leptosol (107.13ha) and EpilepticCambisol (humic) at the plateau ( 227.515ha) with2 -5% slope; endoleptic Cambisol (171.2ha),calcaric Leptosol (humic), (27.05ha) and calcaricLeptosol (128.64ha) at the side slope with 30 –50% slope; epi-Leptic Cambisol (calcaric),(24.92ha) and calcaric Cambisol (474.82ha) at thefoot slope with 8 – 15% slope; Regosol (44.85ha)

and calcaric Vertisol (humic), (163.6ha) at thevalley bottom with 3 – 8% slope. However, majorsoils found in the investigated arable land are:Leptosol at the plateau (LU-4); calcaric Cambisol(LU-2) at the foot slope; Regosol (LU-3), calcaricVertisol (humic) (LU-1) at the valley bottom(Figure 2).

Fig 2. Soil distribution for Korir watershed

Fig 3. Land use map of korir area

The soil in LU-1 has a very low EC and Ntotal; lowavailable phosphorous (Pav); medium total organiccarbon content; high CaCO3; very high CEC withmoderately alkaline pH. Soils in LU-2 has a verylow EC; low Ntotal; medium total organic carboncontent; high Pav and CEC; medium alkaline pH.Soils in LU-3 has a very low EC and Ntotal; lowCEC and total organic carbon content; high CaCO3

and Pav; slightly acidic pH. However, major soilsin LU-4 has a very low EC, CEC, and Ntotal; loworganic carbon content; high CaCO3 and Pav;medium pH.

The major land uses of the watershed arecultivated (49.46%), grassland land (4.83%), bushland (31.26%), Deg.bushland (10.63%) and Built-up area (3.82%) (Figure 3).

The area is highly degraded. Sheet and rill arevery common in the cultivated land, grazing and

Copyright © Journal of the Drylands 2010ISSN 1817-3322

217

bush land while gullies are widely spread on thesloppy hill side parts of the catchment. Due toheavy deforestation, expansion of agricultural land,population pressure, over grazing and lack ofproper land use measures, the vegetation cover isvery low.

Land Suitability Evaluation for SurfaceIrrigationThe processing of the parametric evaluation systemfor gravity/surface irrigation gave the results thatare represented in Table 3.

Table 3: Land Suitability for surface irrigationLand units Ci Suitability class1 61.75 S22 44.5 N13 58.21 S34 18.8 N2

As shown in Table 3 and Figure 4, for the surfaceirrigation, there is no area classified as highlysuitable (S1). Only 22.58% (163.604ha) of thestudy area is moderately suitable (S2), 6.19%(44.85ha) marginally suitable (S3), 62.77%(454.82ha) currently not suitable (N1) whereas8.46% (61.27ha) of the study area is classified aspermanently not suitable (N2). The limiting factorto this kind of use is mainly the limited soil depthand texture that is mostly sandy, while surfaceirrigation requires heavier soils.

Fig 4. Land suitability map for surface irrigation

Land Suitability Evaluation for Drip IrrigationThe processing of the parametric evaluation systemfor drip irrigation gave the results that arerepresented in Table 4.

Table 4: Land Suitability for drip irrigationLand units Ci Suitability class1 80.75 S12 57.6 S33 80.75 S14 23.3 N2

For drip irrigation (shown in Table 2 and Figure 5),62.77% (454.82ha) of the area is marginallysuitable (S3) and 28.77 % (208.45ha) is classifiedas highly suitable (S1). 8.46% (61.27ha) of the area

is classified as permanently not suitable (N2).Further, there is no area classified as moderatelysuitable (S2) for drip irrigation. In this case, thehandicap is given by the soil calcium carbonate andbad texture due to a large amount of coarse gravel.The marginally suitable area can be observed in thelargest part of cultivated area due to light soiltexture, shallow soil depth and moderate slope.Moreover, the relative clogging potential of waterused in drip irrigation systems for land units 1 and2 is sever (pH>8.0) and for land units 3 and 4 ismoderate (pH 7.0 – 8.0) as noted in Sijali (2001).

Figure 5. Land suitability map for drip irrigation

DISCUSSIONThe mean capability index (Ci) for surfaceirrigation was 45.815 (marginally suitable) whilefor drip irrigation 60.6 (moderately suitable). Thecomparison of the capability indexes for surfaceand drip irrigation (Tables 3 & 4) indicated that inland unit coded 4, applying surface and dripirrigation systems was the same. In the other landunits coded 1, 2 and 3 applying drip irrigationsystem was most suitable compared with surfaceirrigation systems. Figure 4 and 5 show thesuitability map for surface and drip irrigationsystems in the Korir area by notation to capabilityindex (Ci) for different irrigation systems. As seenfrom this map, the largest part of this area wassuitable for drip irrigation systems.

The results (Table 3 & 4) indicate that byapplying drip irrigation instead of surface irrigationmethods, suitability classes of land unit coded 2(62.77%) can be improved from currently not-suitable (N1) to marginally suitable (S3) andsuitability classes of land unit coded 3(6.1901887%) and 1 (22.58%) improved frommarginally suitable (S3) and moderately suitable(S2) respectively to highly suitable (S1). Thecomparison of the different types of irrigationrevealed that the drip irrigation is more effectiveand efficient than the surface irrigation methods.Provided it is managed properly, drip irrigation issuitable for a large range of crops. Study results(Sijali, 2001) showed that compared tofurrow/surface irrigation; drip irrigation can

Copyright © Journal of the Drylands 2010ISSN 1817-3322

218

achieve 90 – 95% efficiency. Table 5 givescomparative irrigation requirements for meetingcrop demand with the different irrigation methods(adapted from Sijali, 2001). Moreover, this authorsuggested that losses to runoff, deep percolationand evaporation are minimal (most of the irrigationwater is taken up by the plant) when drip irrigationmethod is used.

Table 5. Comparison of typical irrigation requirementsunder well- designed and managed drip and furrowirrigation systems (mm/day)

Net crop waterdemand

Irrigationrequirement (dripmethod)

Irrigationrequirement(furrow method)

3.0 3.3 5.03.5 3.9 5.84.0 4.4 6.74.5 5.0 7.55.0 5.6 8.35.5 6.1 9.26.0 6.7 10.0

Because of the insufficiency of surface water, andthe aridity of the climate, only the drip irrigation isrecommended for a sustainable use of this naturalresource. According to Sijali (2001), drip irrigationis often the favored method of irrigation, forexample on steep and undulating slopes, for poroussoils, for shallow soils, field having various soils,where water is scarce, where water is expensive,and where water is of poor quality. However, themain limiting factors in using surface irrigationmethods in this area are soil texture, soil depth andslope. This corresponds with the results of Sijali(2001) in which, surface irrigation may not beappropriate for porous soils (final infiltration rates>7 cm/h) such as sandy soils, or soils with finalinfiltration rates that are too low (<0.3 cm/h). Themain limiting factors in using drip irrigationmethods in this area are soil calcium carbonatecontent and soil texture. Soil texture provides ameasure for permeability, and to some extent, forwater retention capacity (Wayne et al., 2007). Soilswith potentially high percolation losses and soilswith low water retention capacity and all soils withcoarse textures have been considered not suited forsurface irrigation. Irrigation of dry land cropsrequire well drained soils to assure aeration and toavoid the danger of secondary salinization. Underirrigated conditions, soil depth affects drainage,aeration, and water retention properties. Calciumcarbonate in the soil profile affects soil structureand interferes with infiltration andevapotranspiration processes. It influences both thesoil moisture regime and availability of nutrients(Albaji et al., 2007).

CONCLUSIONSDetails are given for the analysis of the field data tocompare the suitability of different irrigationsystems. The analyzed parameters included soil and

land characteristics. The results showed that dripirrigation is more suitable than surface irrigationmethods for most of the study area. The majorlimiting factor for the drip irrigation methods weresoil calcium carbonate and soil texture. However,for surface irrigation methods soil texture, soildepth and slope were the restricting factors. Dripirrigations can obviously be a way to improve thepractice on light soil textures. On the other hand,because of insufficiency of water in arid and semiarid climate, maximizing water use efficiency isnecessary to produce more crops per drop and tohelp solve the water shortage crisis in theagricultural sector. The shift from surface irrigationto high-tech irrigation technologies, therefore,offers significant water-saving potentials. Finally,since drip irrigation systems typically apply smallamount of water on a frequent basis to maintainsoil water near field capacity, it would be morebeneficial to use drip irrigation methods in thisarea.

ACKNOWLEDGEMENTOur particular gratitude goes to the MekelleUniversity NORAD II Project for their financialand logistics support. We feel great pleasure toexpress my special gratitude to Mr. Mulu Haftu,Mr. Kalayu Berhe, Mr. Aregawi Teka, Mr. KahsayTadelle, Mr. Yirgalem Gebre, and Mr. EskindirGidey for their technical support during the fieldwork. We would also like to thank the farmers,development workers and experts from the Officeof Agriculture and Rural Development (OoARD)and Tabia5 administration of the study site forproviding me with valuable information and fortheir guidance.

REFERENCESAlbaji, M., Boroomand Nasab, S., Kashkoli, H. and

Naseri, A.A. 2007. Comparison of differentirrigation methods based on the parametric

evaluation approach in West Shoush Plain,Iran. Journal of the InternationalCommission on Irrigation and Drainage.

Bazzani, F. and Incerti, F. 2002. Land evaluation inthe province of Larache, Morocco. 22ndCourse Professional Master Geomaticsand Natural Resources Evaluation. 12 Nov2001-21 June 2002. IAO, Florence, Italy.

Berry, Quirine Ketterings, Steve Antes, Steve Page,Jonathan Russell-Anelli, Renuka Rao andSteve DeGloria, 2007. Nutrient ManagementSpear Program. Department of Crop and SoilSciences, College of Agriculture and LifeSciences. Cornell University CooperativeExtension.

Bienvenue, J.S., Ngardeta, M. and Mamadou, K.2003. Land Evaluation in the Province of

5 Tabia is a sub-district of roughly five thousand residents. Regarded asthe lowest administrative unit.

Copyright © Journal of the Drylands 2010ISSN 1817-3322

219

Thies, Senegal. 23rd Course ProfessionalMaster. Geomatics and Natural ResourcesEvaluation. 8th Nov 2002-20 June 2003. IAO,Florence, Italy.

Bond, W. J. 2002. Assessing Site Suitability for anEffluent Plantation in Mckenzie. Soil PhysicalMeasurement and Interpretation for LandEvaluation. CSIRO Publishing, pp. 351–359.

Briza, Y., Dileonardo, F. and Spisni, A. 2001. LandEvaluation in the Province of Ben Slimane,Morocco. 21st Course ProfessionalMaster.Remote Sensing and Natural ResourceEvaluation. 10 Nov2000 - 22 June 2001.IAO, Florence, Italy.

Dengiz, O. 2006. A Comparison of DifferentIrrigation Methods Based on the ParametricEvaluation Approach. Turk J. Agric. For.30:21–29.

FAO, 1990. Guidelines for soil description. FAORome, pp. 69.

FAO, 1998. World reference base for soilresources. FAO Rome, pp. 88.

Foty k, 1993. Acacia, Quarterly-44 FF/N, Number7. GJED-TOVE. BP110 KPALIMETOGO.

Hargreaves, H.G. and Mekley, G.P. 1998.Irrigation fundamentals. Water ResourcePublication, LLC, 200 p.

Hired, C., Thomson, A. and Beer, I. 1996.Selection and Monitoring of Sites Intended forIrrigation with Reclaimed Water inProceedings. Water TECH, Sydney. May

1996. Australian Water andWastewater Association, Sydney, Australia.

Hunting. 1976. Tigray Rural Development Report.Hemel Hempstead, Hertfordshire, UK:Hunting Technical Service.

Mbodj, C., Mahjoub, I. and Sghaiev, N. 2004. LandEvaluation in the Oud Rmel Catchment,Tunisia. 24th Course ProfessionalMaster. Geomatics and Natural ResourcesEvaluation. 10th Nov 2003–23 rd Jun.

Naseri A., Rezania A.R., and Albaji M. 2009.Investigation of Soil quality for differentirrigation systems in Lali Plain, Iran. Journalof Food & Environment Vol.7 (3&4): 955 –960. WFL Publisher. Science and Technology

SFPT, 2003. Draft Genfel Tabia Land Use Plan.GFA-terra systems.

Sijali IV, 2001. Drip Irrigation: Options forSmallholder Farmers in Eastern and SouthernAfrica. RELMA Technical Handbook Series24. Nairobi, Kenya: Regional LandManagement Unit (RELMA), SwedishInternational Development CooperationAgency (Sida). Pp 60.

Sys I., Van Ranst E., and Debaveye J. (1991) -Land evaluation, part II. Methods in landevaluation. Agriculture publications n.7,General Administration for DevelopmentCooperation. Brussels, Belgium pp. 70-76.

Tesfai, M. 2002. Land suitability system for spateirrigation schemes in Eritrea. Soil UseManagement 18:77-78.