the performance of selected soil and water conservation...

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The performance of selected soil and waterconservation measures—case studies from Ethiopia

and Eritrea

Karl Herweg ), Eva LudiCentre for DeÕelopment and EnÕironment, UniÕersity of Bern, Hallerstrasse 12, CH-3012 Bern, Switzerland

Received 14 October 1997; received in revised form 15 December 1998; accepted 15 December 1998

Abstract

This paper investigates the performance of selected soil and water conservation measures in thehighlands of Ethiopia and Eritrea, namely Fanya Juu, soilrstone bund, grass strips and doubleditches. The impact of these techniques on runoff, soil loss, crop yield and biomass production ismeasured at on-farm experimental sites in seven research sites under different agro-ecologicalconditions. On one hand, most measures brought about a considerable reduction in soil loss andrunoff. The latter, however, increases the waterlogging hazard, particularly in sub-humid environ-ments. On the other hand, crop yield and biomass production did not increase, as it would havebeen necessary to compensate for the high costs of soil conservation. Thus, the measures testedonly partially fulfil their requirements. To enhance their adaptability to local conditions, they mustbe supplemented with biological and agronomic measures that help improve production. q 1999Elsevier Science B.V. All rights reserved.

Keywords: Soil and water conservation; Soil erosion; Soil loss; Runoff; Food production; On-farm research;Ethiopia; Eritrea

1. Introduction

Ž .In the 1970s and 1980s, soil and water conservation SWC campaigns under theŽ .umbrella of the World Food Programme ‘Food for Work’ were started to combat

severe soil degradation in the highlands of Ethiopia and Eritrea. Thus, most SWC effortsfocused on highly degraded areas with limited production potential. Marginal steep lands

) Corresponding author. Fax: q41-31-631-85-44; E-mail: [email protected]

0341-8162r99r$20.00 q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0341-8162 99 00004-1

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were terraced with a few mechanical SWC measures. Subsistence farmers in need offood aid were the labour force. Decisions on which type of SWC measures to use andwhere to construct them were not made by the farmers concerned, and only rarely wasan attempt made to include their indigenous experience and knowledge.

Ž .The main SWC measures introduced on cultivated land were the soil or stone bundand the Fanya Juu type terrace. Both techniques consist of a small dam and a ditch. Toconstruct a bund, the excavated material of the ditch is moved ‘downhill’ to build a dam,

Ž .while Fanya Juu is the Swahili expression for ‘throw uphill’ cf. Fig. 2 . With on-goingsoil erosion, both measures eventually build up to bench terraces. The Fanya Juu typeterrace has been developed in Kenya as a modified form of the contour terraceŽ .Bergsma, 1996, p. 99 . Both measures have been widely implemented on small,

Ž .labour-intensive farms Bergsma, 1996, p. 187 , but not without adaptation problemsŽ .Kamar, 1998, p. 1060 f. . The particular attractiveness of the Fanya Juu is that level

Ž .terraces can develop in as little as 7 years Hudson, 1988, p. 121 .Meanwhile, there is a wealth of experience with mechanical SWC in Africa, for

example in semi-arid regions, where moisture conservation is the most important aspectŽ .of the measures IFAD, 1992; Serpantie and Lamachere, 1992; Reij et al., 1996 .´ `

Climatic conditions such as low or variable rainfall and high evaporation usually limitthe variety of biological SWC options. In contrast, sub-humid areas have a higher

Ž .potential for biological–agronomic SWC e.g., Gasser, 1990; Quansah, 1990 , which isless costly, improves infiltration and enhances soil organic matter, and thus turns out tobe more productive. However, biological measures often fail to produce sufficientground cover during the onset of the rains after the dry season or drought period. Inorder to bridge these periods of high erosion hazard, mechanical SWC is often the onlymeans to protect the soil.

While implementing mechanical SWC in Ethiopia and Eritrea, three assumptionsŽ .were commonly made: 1 without SWC, erosion will decrease production in the

Ž . Ž .long-run; 2 with SWC, production will stabilise or increase; 3 the expected stabilisa-tion or increase in production will be an incentive in itself for farmers to maintain SWCstructures. However, another development took place starting with political changes in

Ž . Ž .1991 Herweg, 1992 . As long as there was an incentive food which could even beŽused as a source of income, the livelihood of the local communities was secured Tato,

.1992 and farmers tolerated the SWC structures on their land. In many semi-arid areasthere is a tendency to maintain SWC structures because moisture conservation is of

Žcrucial importance for crop production. In some parts of the sub-humid highlands e.g.,.Welayta , a partial modification of SWC and integration into the complex indigenous

Žland management system was observed, while in other parts Kembata and Northern.Shewa a considerable number of SWC structures were removed. Based on the results of

on-farm experiments and additional observations, this paper explains some of the mainreasons for the above-mentioned developments.

2. Methodology

In order to support and monitor SWC efforts in the highlands, the Governments ofŽ .Ethiopia and Switzerland created the Soil Conservation Research Programme SCRP in

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1981. The SCRP started with a wide range of observations and experiments in sevenŽ . Ž .research areas Herweg and Hurni, 1993 . At each SCRP research site Fig. 1 , an

on-farm experiment was established to monitor the impact of different SWC measuresŽ .on soil loss, runoff, crop yield, and biomass production Fig. 2 . Fanya Juu and

soilrstone bunds were widely implemented terrace types. At some research sites, bothŽ . Žtypes were tested in two variations: level on the contour and graded with a gradient of

.about 5% for drainage of excess water . In addition, grass strips were newly introducedŽ .as a more cost-effective practice. In the semi-arid area of Afdeyu Eritrea , the level

double ditches which were designed to enhance moisture conservation, replaced thegrass strip.

At each research site, one block of four or six plots is established on-farm in order totest three or five SWC measures against the respective local cultivation practice of the

Ž .farmer control plot . Each plot or treatment accommodates two or three SWC structureson an area 6 m wide and 30 m long. The blocks measured 24 m=30 m, and 36 m=30m,, respectively. The replication of such a block is not possible for several reasons. Onone hand, due to the rugged highland topography, soil properties and slope angleschange on a small scale. On the other hand, farm size is on average below 1 ha, so that areplication would involve different farmers, crop rotations, and farm operations. Thus,the inherent variations of each plot cannot be investigated. The plots are constructed

Fig. 1. SCRP research sites in the highlands of Ethiopia and Eritrea.


Fig. 2. SWC measures tested at SCRP research sites—cross-sections in the construction stage.

with removable borders to allow uniform soil management and crop rotation on theentire block. Crop rotation and timing of farm operations are determined by the farmer.

Soil loss and runoff from each plot flow into a set of two collection tanks downslope.The rates are computed from the measurement of water depth, soil, and suspendedsediment in the tanks. A range of systematic and random data errors, parameterestimation errors, and model errors determines the accuracy of soil loss and runoff

Ž .values Herweg and Ostrowski, 1997 . For single erosion periods, data accuracy rangesbetween "2–5% for runoff and "6–16% for soil loss, respectively. The accuracy ofannual data, in contrast, improves to "0.1% for runoff and y3% for soil loss,respectively.

Production data are computed from the harvest of the entire plot area. After themeasurement, grain and biomass are returned to the farmer. In comparison with thecontrol plot, the treated plots have a reduced production area because the SWCstructures occupy about 10% of the area. The production data thus reflect the net gainfor the farmer, both with and without SWC.

The observation period was basically designed to last 5 years, with irregularities dueŽ .to the civil war and insecurity cf. Table 1 . The results of the on-farm experiments were

combined with information obtained through informal interviews with farmers, which

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Table 1SWC-oriented classification of the SCRP sites

Research site Altitudinal SWC-class Annual precipitation Mean Dry Dryrange in m.a.s.l. annual season months

Mean Standard Coefficient erosivity in winter betweenŽ .mm deviation of variation aŽ . Ž .Jrm h months rainy

Ž . Ž .mm % bseasons

X XŽ .Afdeyu Af 2 438–2 540 1 semi-arid 382 107 29 230 9 –X XŽ .Hunde Lafto Hu 1 963–2 315 2 sub-humid with 935 205 22 346 5 1X X XŽ .Maybar Ma 2 530–2 858 insecure rainfall 1 211 247 20 420 4 1X X XŽ .Andit Tid At 3 040–3 548 3 sub-humid with 1 358 243 18 506 4 1X X XŽ .Anjeni Aj 2 407–2 507 secure high rainfall 1 690 155 9 633 5 –X X XŽ .Gununo Gu 1 982–2 103 1 314 255 19 582 3 –X X XŽ .Dizi Di 1 565–1 789 1 512 124 8 646 4 –

a Mean monthly precipitation less than 50 mm.b Mean monthly precipitation less than 75 mm.Period of observation: Af, 1985–1990; Hu, 1983–1990; 1993; Ma, 1982–1989; 1992–1993; At, 1983–1992; Aj, 1985–1990; 1992–1993; Gu, 1982–1992; Di,1989–1993.Interruptions are due to war and instability.


shed some light on their perception of the SWC measures. A soil profile analysis andother field observations complete the findings.

3. Results

ŽWith regard to SWC, the SCRP research sites were grouped in three classes Table. Ž .1 : 1 Semi-arid areas, with a mean annual precipitation below 500 mm and a mean

annual erosivity below 300 Jrm h, where priority was given to water conservationŽ . Ž .Afdeyu ; 2 Sub-humid areas, with insecure rainfall, a mean annual precipitationbetween 500 and 1300 mm and a mean annual erosivity between 300 and 500 Jrm h,

Ž .where both soil conservation and water-retention are important Maybar, Hunde Lafto ;Ž .3 Sub-humid areas, with secure high rainfall, a mean annual precipitation above 1300mm and a mean annual erosivity above 500 Jrm h, where priority was given to soil

Ž .conservation and drainage of excess water Andit Tid, Anjeni, Gununo, Dizi .

3.1. The desired impacts of SWC

Before interpreting the performance of the SWC technologies tested, the criteria andthe desired impacts have to be defined. Except for runoff, the desired impact is obvious:production should increase and soil loss should decrease. Runoff, in contrast, is a morecomplicated issue and needs to be evaluated with care! Runoff reduction results in lowersoil loss rates, but at the same time, it may cause waterlogging on terraced land in highrainfall areas, which affects production of certain crop types as well as the adaptation ofthe technology. Thus, in semi-arid areas, runoff reduction is desirable, while in the

Ž .sub-humid areas, it should not be reduced at all or only slightly reduced up to 10% .

3.2. General interpretation

Ž .The mean annual soil loss and runoff values Tables 2 and 3 reveal a comparativelyŽlow erosion hazard in sub-humid areas with insecure rainfall Hunde Lafto, Maybar,

.SWC-class 2 . A relatively high erosion hazard is expected for semi-arid conditionsŽ .Afdeyu, SWC-class 1 and those sub-humid areas with secure high rainfall located at

Ž .higher altitudes Andit Tid, Anjeni, SWC-class 3 . Despite high annual rainfall andŽ .erosivity, low soil loss rates were measured in Gununo and Dizi SWC-class 3 , where

Ž .the lower altitude cf. Table 1 implies more moderate temperature, higher biodiversity,and more rapid development of protective ground cover.

To assess the impact of the SWC treatments, soil loss, runoff, crop yield and biomassvalues of the respective control practice were set at 100%. On this basis, the reduction or

Ž . Ž .increase in percent was calculated for each treatment Table 4 . It should be noted thatthis analysis was restricted to the average performance over the entire period ofobservation. A trend analysis from the first year of observation to the last was notincluded because the impact of the treatments on soil loss, runoff and production wasdistorted by the year-to-year variations of rainfall, erosivity, and crop type.

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Table 2Annual soil loss and runoff under local cultivation practices

Ž .Research site Soil unit slope % Soil erosion under local cultivation practice Years of soil No. of croplossrrunoff yieldr biomassŽ . Ž .Annual runoff mm Annual soil loss trha

ameasurement measurementsŽ . Ž .Mean range Mean range Standard Coefficient

deviation of variationŽ .%

Ž . Ž . Ž .Afdeyu chromic Cambisols 31 162 34–359 42 3–114 51 122 3 –Ž . Ž . Ž .Hunde Lafto pellic Vertisol 21 12 1–18 7 0–16 7 95 3 7

Ž . Ž . Ž .Maybar haplic Phaeozem 28 24 17–30 2 1–4 1 61 4 7Ž . Ž . Ž .Andit Tid eutric Regosol 24 354 183–688 48 2–140 50 104 5 5

b Ž . Ž . Ž .Anjeni I vertic Luvisol 28 487 359–620 110 59–167 29 26 grass grassstrip 3, strip 3,others 5 others 7

b Ž . Ž . Ž .Anjeni II eutric Nitosol 12 482 365–645 90 17–176 69 76 grass grassstrip 3, strip 4,others 5 others 10

Ž . Ž . Ž .Gununo humic Nitosol 14 131 50–262 11 1–22 8 71 5 6Ž . Ž . Ž .Dizi haplic Lixisol 18 45 9–139 5 0–25 10 195 5 6

a There may be more than one harvest per year.bAnjeni contains two experimental set-ups on 28% and 12% slopes, respectively.

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Table 3Mean annual soil loss and runoff for different SWC measures and local cultivation practices

Ž . Ž .Research site Mean annual soil loss trha Mean annual runoff mm

Local Graded Graded Grass Level Level Local Graded Graded Grass Level Levela acultivation Fanya Juu bund strip Fanya Juu bund cultivation Fanya Juu bund strip Fanya Juu bund

practice practice

Afdeyu 42 – – 8.0 7.2 13.8 162 – – 87 64 85Hunde Lafto 7.2 3.3 2.4 2.9 0.0 0.0 12.1 20 15.9 6.6 0.6 0.7Maybar 1.9 1.8 3.3 0.9 0.5 1.2 25 27 36 16.7 12.8 18.5Andit Tid 48 17.8 29 13.0 6.0 6.9 354 348 335 236 194 133Anjeni I 28% 110 36 38 – – – 487 325 331 – – –Anjeni II 12% 90 17.1 34 – – – 482 239 290 – – –Gununo 11.4 0.8 1.3 1.9 0.2 0.3 131 38 62 58 9.3 19.8Dizi 5.1 0.5 0.7 1.5 0.8 0.2 45 18.3 27 19.6 32 15.3

a In Afdeyu, the level double ditch replaced the grass strip.

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Table 4The average impact of SWC measures on soil loss, runoff, crop yield and biomass compared with local cultivation practicesa

Research site Graded Graded Grass Level Level Graded Graded Grass Level Levelb bFanya Juu bund strip Fanya Juu bund Fanya Juu bund strip Fanya Juu bund

Ž . Ž .Relative impact on soil loss % Relative impact on runoff %U U Ub aŽ .Afdeyu Af – – I81 I83 I67 – – I46 I60 I47

U U U UŽ .Hunde Lafto Hu I54 I67 I60 I100 I100 q65 q31 y45 y95 y94U U U UŽ .Maybar Ma I4 q73 I55 I72 I37 H8 q46 y33 y48 y25

U U UŽ .Andit Tid At I63 I41 I73 – – I2 I5 y33 – –U U UŽ .Anjeni I 28% Aj I68 I66 I72 – – y33 y32 y41 – –U U UŽ .Anjeni II 12% Aj I81 I63 I57 – – y50 y40 y19 – –U U UŽ .Gununo Gu I93 I88 I84 – – y71 y53 y55 – –U U UŽ .Dizi Di I91 I87 I71 – – y59 y40 y57 – –

d dŽ . Ž .Relative impact on crop yield production % Relative impact on biomass production %cŽ .Afdeyu Af – – – – – – – – – –Ž .Hunde Lafto Hu H7 H15 y4 H4 H12 H6 y2 H7 H7 H12

Ž .Maybar Ma y22 y27 y24 y28 y30 y22 y25 y23 y21 y26Ž .Andit Tid At y50 y12 y39 – – y45 y11 y37 – –

Ž .Anjeni I 28% Aj H4 y13 0 – – y5 y13 H8 – –Ž .Anjeni II 12% Aj H14 y6 H14 – – H5 y12 H11 – –

Ž .Gununo Gu H13 H5 H16 – – H22 H12 H16 – –Ž .Dizi Di y17 y39 y20 – – H2 y22 y18 – –

a Period of observation: Af, 1988–1990; Hu, 1989–1990, 1993; Ma, 1986–1989; At, 1987–1991; Aj, 1986–1990, 1992; Gu, 1987–1991; Di, 1989–1993.b In Afdeyu, the level double ditch replaced the grass strip.c In Afdeyu, in accordance with the farmer’s decision, all plots were left fallow.d Ž 2 .The area for yield and biomass measurement is always the entire plot 180 m .U

Significant difference at p-0.05 for soil loss using Wilcoxon Signed Rank Test.Ž .Bold indicates whether the desired impact increaserdecrease, " was achieved.


Fig. 3. Cumulative soil loss and runoff on a 28% slope in Anjeni, 1990. The impact of the graded Fanya Juu,the graded bund and the grass strip on soil loss and runoff is shown, using a double mass curve. There is

Ž .considerable soil loss reduction compared to the control plot cf. Tables 4 and 5 . The reduction in runoff, onthe other hand, may increase the waterlogging hazard and thus affect crops such as barley and beans.

3.3. Soil loss

Significance was tested only for soil loss as the most important indicator in the study.Ž .The Wilcoxon Signed Rank Test p-0.05 showed significantly smaller soil losses for

the majority of SWC treatments when compared with the respective local cultivationŽ .practices control site . But there are no significant soil loss differences between most

Ž .SWC treatments, and so there is no ‘best’ measure as such Fig. 3, Table 5 . Despite thisconsiderable soil loss reduction, absolute erosion rates can still be very high, even underSWC. More than 30 trha in Anjeni, 10 trha in Andit Tid, and 7 trha in Afdeyu wererecorded in single years. A considerable proportion of such high annual values was

Ž . Žcaused during a few rainfall periods. As much as 10 trha Andit Tid , 6 trha Hunde. Ž .Lafto, Anjeni and 1 trha Gununo, Dizi, Maybar, Afdeyu of soil loss were observed

Table 5Absolute and relative annual soil loss and runoff on a 28% slope in Anjeni, 1990

Experimental plot I, 28% slope

Local cultivation Grass Graded GradedŽ .practice control strip Fanya Juu bund

Ž .Soil loss absolute trha 104 16 23 15aŽ .Soil loss relative % 100 15.4 22.1 14.4

Ž .Runoff absolute mm 502 263 292 244aŽ .Runoff relative % 100 52.4 58.2 48.6

a In relation to the control plot values which are set at 100%.


during such periods, encompassing between one and three rainstorms. Therefore,absolute soil erosion rates might still be above a given tolerance level and call forfurther development of SWC technology.

3.4. Runoff

Ž .Runoff was considerably reduced at the semi-arid site of Afdeyu SWC-class 1 andŽthus the goal of moisture conservation was met. For SWC-class 2 Maybar, Hunde

.Lafto , the impact of SWC on runoff reflects a possible dilemma. On one hand, gradedstructures increase runoff. This may cause erosion of the drainage ditches during seasonswith high rainfall, while precious moisture may be lost during cropping seasons withsub-average rainfall. On the other hand, level structures decrease runoff, which isdesirable in times of drought stress but may increase the probability of waterlogging andbreakage of SWC structures during high rainfall periods. For SWC-class 3, runoffreduction is generally considered too high in view of the increased waterlogging hazard.

3.5. Production

The on-farm experiment involved the Fanya Juu, bund, grass strip or double ditchmeasure, respectively, but did not include any additional agronomic or biologicaltechniques. So, it may not be surprising that, in contrast to the assumptions explained inthe introduction, production—the most important factor for farmers—rarely increasedduring the first three to 5 years of SWC. However, except for Andit Tid and DiziŽ .SWC-class 3 , production remained relatively stable under the SWC structures tested,

Ž .which was reflected by only slight changes decreaserincrease in crop yield andbiomass compared to the control site. The reasons for this will be discussed in Section 4.

4. Additional observations

SWC structures can have an entirely different impact and consequently, a differentdegree of adaptation if they are transferred to other biophysical andror socio-economic

Ž .conditions Herweg, 1995 . Therefore, qualitative observations and statements of farm-ers from within and in the surroundings of the SCRP research sites supplemented theresults from the on-farm experiment. In particular, farmers in areas of secure high

Ž .rainfall SWC-class 3 had serious complaints about mechanical conservation structuresŽ . Ž .Tegene, 1992; Ludi, 1997 . The main arguments are that: i SWC structures occupy

Ž .precious cropping area; ii the area occupied by SWC structures is not ploughed, weedsŽ .and rodent habitats are no longer destroyed, and cultivated fields are infested; iii

despite a drainage gradient of 2% or higher, waterlogging is frequently observed along aŽ .narrow strip above the SWC structures; iv maintenance requires unacceptable labour

Ž .inputs; v farmers have problems carrying out their traditional farm operations. Narrowterrace spacing makes it difficult or impossible to plough the slope in diagonal lines andturn the ox-drawn plough.


Ž .Field observations and a detailed soil survey Kruger, 1994 support these complaints.¨Given an average spacing of 10 m between two Fanya Juu structures, for example, the

Ž .crop production on about 15% of the total area is affected during the first years Fig. 4 .An additional 10 to 15% of the production area may be affected by waterlogging.Furthermore, weeds and rodents can affect production on the entire terraced area. Thearea where production might be affected in one way or another increases on steeperslopes with narrow terrace spacing, while it may slightly decrease in the long-run as theterraces develop. The SWC structure itself can be used for fodder and woody biomassproduction. But this can hardly replace food production for a subsistence farmer.

Under both the soil bund and the Fanya Juu type terrace, the lowest crop yield ismeasured below the structure. A change in the soil profile and increasing spatialvariability of soil fertility are considered the major reasons for this. In the course of theerosion process that forms the terrace, the topsoil below the structure is gradually moved

Ž .downslope and accumulates above the next SWC structure Kruger, 1994 . This process¨Žis accelerated through tillage erosion, particularly under hoe cultivation Turkelboom et

. Ž .al., 1997, p. 41 , and less when using the Ethiopian ox-plough Maresha that merelyscratches the surface. If the topsoil is completely eroded, the subsoil will also move

Fig. 4. Soil profile changes and reduction of production area on a Fanya Juu terrace.


Fig. 5. Differences in terrace development with soil bunds and Fanya Juu.

downslope on top of the fertile accumulation. In other words, topsoil reduction belowŽ .the SWC structure further affects or reduces the area of crop production Fig. 4 .

Different SWC structures have different implications with respect to labour input andŽ .the utilisation of fertile soil accumulation Fig. 5 . Firstly, the soil bund requires less

labour input because the excavated material from the ditch is thrown downhill. How-ever, accumulations of fertile topsoil may block the drainage; eventually, they maycause waterlogging or be washed away. Moreover, instead of being used for foodproduction, accumulations are used to raise the bund during maintenance in thefollowing years. Secondly, drainage of the Fanya Juu is much less affected byaccumulated material, and the dam is mainly built from subsoil material. But establish-ing and maintaining a Fanya Juu is much more labour-intensive since soil must bemoved uphill. Thirdly, the grass strip does not require high labour input since it does notinvolve moving soil to raise the structure. It drains well because water can penetrate theentire strip. However, terrace development takes longer compared to the other SWCstructures.

5. Conclusions and recommendations

Reduction of soil loss was considerable at all stations and with most SWC measures,although absolute erosion rates were still high in some cases. Runoff control, bycontrast, requires greater emphasis during the design of SWC structures.


. Ž .SWC-class 1: In semi-arid areas e.g., Afdeyu , level SWC structures did a goodŽ .job conserving moisture. However, in Lesotho Wenner, 1989, p. 67 found that many

large rills and gullies on terraces developed because of level terracing. He thereforerefrains from advocating level earth terraces in general. Instead, these terraces could beimproved as described for SWC-class 2.

. Ž .SWC-class 2: Sub-humid areas with insecure rainfall e.g., Maybar, Hunde Laftoare principally subject to two extremes. Excesses and shortages of water can follow eachother closely. In this case, SWC aims to achieve a compromise. Since there is always aprobability of excess rainfall, SWC structures need a gradient. To ensure water retentionduring dry spells, supplementary structures such as tied ridges are useful. These

Ž . Ž .structures should be breakable during high rainfall events. Wenner 1989 p. 86suggests adding small ditches in the middle of the production area to increase infiltrationand to decrease overtopping of the structures.

. ŽSWC-class 3: For sub-humid areas with secure high rainfall e.g., Dizi, Gununo,.Anjeni, Andit Tid , structures must have a gradient to safely drain excess water. In this

case, the waterways in particular need to be protected from incision and gully erosion.These recommendations give the extension service clues about which directions to

take when seeking suitable SWC technologies. For the farmers, however, what counts isproduction, and for the subsistence farmers it is mainly the production of the currentseason that guarantees the mere survival of their families. As pointed out by HurniŽ . Ž .1988 p. 103 , SWC is a reproductive process, which unfortunately involves short-termcosts, while benefits can only be expected in the long-run. SWC has rarely been in theshort-term interest of land users because it often shows a negative net present valueŽ .NPV, Kappel, 1996 . This is due to the unfavourable distribution of costs and benefits.

Ž .Tegene 1992 reports for Gununo area that farmers would not even consider a yieldincrease acceptable compensation for losing productive land occupied by SWC struc-tures.

The need to keep conservation costs low and to increase production calls forintensified production, supported for example, by agronomic and biological SWC.Generally, soil cover is considered a highly efficient means of controlling erosion, at

Ž .least as effective as the runoff barrier approach, but less costly Young, 1989, p. 38 .However, one should not draw the conclusion that biological SWC can entirely replacemechanical structures, because it is not possible to maintain permanent vegetation coverin agricultural production systems. Further SCRP test plot experiments recorded soillosses as high as 10 trha during high erosivity rainfall periods with 65% plant cover,while 5 trha were observed at different stations, even with 75 to 85% plant cover. Itcannot be denied that plant cover serves to reduce soil erosion. However, particularlyduring extreme rainfall periods that may be responsible for the greater part of the annualsoil loss, plant cover may not be a sufficient protection. Similarly, runon from upslopeareas often causes rill and gully erosion and may not be prevented by biologicalmeasures alone. Thus, mechanical structures are an indispensable component of SWCfor control of drainage and erosion, both during times of low and high vegetation cover.

The considerable effect of the measures tested during on-farm experimentation inreducing soil loss should be taken as a point of departure, because one cannot afford toloose more soil resource as an important asset for agricultural production. But it is


essential to develop suitable combinations of mechanical, agronomic, and biologicalSWC practices which can raise production. At present, the greatest difficulty seems tobe developing such solutions for sub-humid areas with secure high rainfall and climatic

Žlimitations on biological SWC e.g., high altitudes with low temperature, or steep slopes.with shallow soils .

Successful SWC is frequently connected with the following attributes: technicalfeasibility and adaptability, ecological soundness, economic viability, and social accep-tance. To achieve a reasonable compromise among these attributes, experiments like theone discussed in this paper can be considerably improved, so that the preparation of theexperiment probably becomes more important than the monitoring itself. Farmers, as theimplementers of SWC, must have a say in which measures should be tested. Ideally,farmers and researchers select the most promising indigenous—i.e., already accepted—techniques together, and improvements are negotiated on this basis. SWC measures needto be designed and monitored together with farmers so that they can be incrementallyimproved.

Many of the above conclusions, e.g., to achieve SWC by increasing production orŽ .popular participation, are not new at all. For example, Hagmann 1996 provides an

example from Zimbabwe indicating similar acceptance problems of SWC due totechnical difficulties. Already in the 1980s, recommendations were made in Ethiopia toaddress land tenure issues, to develop a multi-sectoral strategy, or provide infrastructure.

Ž .Hurni 1993 developed several possible scenarios and options for the management ofthe land resource, stating that sustainable land management is more than mere techno-logical development. There is a great demand for improvement of the socio-economicand political framework so that it enables farmers to use their land in a sustainablemanner. Although these proposals are not new, improved socio-economic conditions arefar from being achieved. Consequently, the failure of purely technical approaches canalso be expected in the future, and this will cause increasing socio-economic problems.

Acknowledgements

The authors wish to thank all the colleagues of the SCRP, particularly Prof. Dr. HansŽ .Humi CDE Bern who designed and initiated the experiment under discussion. The

Ž .Swiss Agency for Development and Co-operation SDC and the Government ofEthiopia have generously funded the SCRP for many years. Special thanks go to Prof.

Ž .Dr. M.W. Ostrowski University of Darmstadt for many valuable inputs and discus-sions.

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the performance of selected soil and water conservation...

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