Combined effect of soil bund with biological soil and water conservation measures in the northwestern Ethiopian highlands

Ecohydrology & Hydrobiology 14 (2014) 192–199

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Original Research Article

Combined effect of soil bund with biological soil and water conservation measures in the northwestern Ethiopian highlands Tadele Amare a,b, Assefa Derebe Zegeye a,c, Birru Yitaferu a,*, Tammo S. Steenhuis c, Hans Hurni b, Gete Zeleke d a

Amhara Regional Agricultural Research Institute (ARARI), P.O. Box: 527, Bahr Dar, Ethiopia Centres for Development and Environment (CDE), Institute of Geography, University of Bern, Switzerland Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA d Water and Land Resources, Addis Abeba, Ethiopia b c

A R T I C L E I N F O

A B S T R A C T

Article history: Received 24 September 2013 Accepted 14 July 2014 Available online 29 July 2014

Excessive runoff and soil erosion in the upper Blue Nile Basin poses a threat that has attracted the attention of the Ethiopian government because of the serious on-site effects in addition to downstream effects, such as the siltation of water harvesting structures and reservoirs. The objective of the study was to evaluate and recommend effective biophysical soil and water conservation measure(s) in the Debre Mewi watershed, about 30 km south of the Lake Tana. Six conservation measures were evaluated for their effects on runoff, soil loss, and forage yield using runoff plots. There was a significant difference between treatments for both runoff and soil loss. The four-year average annual soil loss in the different plots ranged from 26 to 71 t ha1, and total runoff ranged from 180 to 302 mm, while annual rainfall varied between 854 mm in 2008 and 1247 mm in 2011. Soil bund combined with elephant grass had the lowest runoff and soil loss as compared to the other treatments, whereas the untreated control plot had the highest for both parameters. As an additional benefit, 2.8 and 0.7 t ha1 year1 of dried forage was obtained from elephant and local grasses, respectively. Furthermore, it was found that soil bund combined with Tephrosia increased soil organic matter by 13% compared to the control plot. Soil bund efficiency was significantly enhanced by combining them with biological measures and improved farmers’ perception of soil and water conservation measures. ß 2014 European Regional Centre for Ecohydrology of Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

Keywords: Soil and water conservation Erosion plot Forage yield Runoff Soil loss

1. Introduction The extent of land degradation in Ethiopia has been described as a pressing challenge for the country’s

* Corresponding author. Tel.: +251 058 220 5200; fax: +251 058 226 6077; mobile: +251 0912 027600. E-mail address: [email protected] (B. Yitaferu).

economy (Hurni, 1993). Two million hectares of land had been severely degraded (Jagger and Pender, 2003) and the amount of soil loss from all land use types in Ethiopia and Eritrea has been estimated as 1.5 billion ton annually, corresponding to an average of 42 t ha1 year1 (Hurni, 1987). In the study area, Zegeye et al. (2010) found about 36 t ha1of soil loss annually from cultivated lands. Hurni (1993) estimated an annual crop yield reduction of 1–2% in Ethiopia due to soil erosion compared to 0.3% of global

http://dx.doi.org/10.1016/j.ecohyd.2014.07.002 1642-3593/ß 2014 European Regional Centre for Ecohydrology of Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

T. Amare et al. / Ecohydrology & Hydrobiology 14 (2014) 192–199

average (den Biggelaar et al., 2003). Moreover, soil erosion leads to off-site effects such as the siltation of lakes, reservoirs, and rivers. Accordingly, the cost of land degradation in Ethiopia is high (Bojo¨, 1996). Despite the long term prevalence of land degradation, the Ethiopian government has become aware of the problems only after the extended droughts of 1973/1974 and 1984/1985 (Kru¨ger et al., 1997). Since then, great efforts have been undertaken to conserve soil and water resources (Gebremichael et al., 2005; Herweg and Ludi, 1999; Sutcliffe, 1995). Such conservation efforts have been reversing the situation of land degradation in the country. For example, Herweg and Ludi (1999) summarized soil and water conservation (SWC) results achieved in 7 study sites of the former Soil Conservation Research Program (SCRP) in Ethiopia. They showed a significant reduction of soil and water loss as a result of applied conservation measures. Gebremichael et al. (2005) found that stone bunds in the Tigray region, northern Ethiopia, led to a 68% reduction of annual soil loss. Likewise, in Tigray, Vancampenhout et al. (2006) observed a yield increase of 7% on land treated with stone bunds compared to untreated areas. Research and development services in Ethiopia have focused only on physical SWC structures without integrating biological measures. Moreover, the adoption of these physical structures by farmers has been continued as a challenge due to the land occupied by physical SWC structures such as soil bunds which they perceived as land loss (Million and Kassa, 2004; Damtew, 2006; Kassie et al., 2008; Adimassu et al., 2012). Hence, rigorous research to enhance the efficiency and productivity of soil bund combined with biological measures is critically important. Selection of plant species that could be integrated with soil bund for their wider adaptability, better economic value and efficiency to reduce soil erosion is highly demanded (Adimassu et al., 2012). The efficiency of vetiver grass, elephant grass, and Tephrosia have been rarely studied for enhancing physical SWC measures such as soil bund in Ethiopia. Vetiver grass was introduced in 1971 from Tanzania and then widely distributed throughout Ethiopia (Kebede and Yaekob, 2009). Babalola et al. (2007), Dalton et al. (1996), and Grimshaw (1993) reported about the importance of vetiver grass in reducing soil erosion. In addition to the suitability study of elephant grass for gully rehabilitation by Alemu et al. (1997) and Yitaferu (1998), about 17.7 t ha1 year1 dry biomass can be produced (Zewudu and Hassen, 1998). According to Guto et al. (2011, 2012) the nature of root and shoot structure of elephant grass helped to conserve soil and water better than Leucaena. Tephrosia is a nitrogenfixing shrub that has been introduced from Kenya for green manure purpose. It has shown wider adaptability with high biomass yield that could be used as a green manure (Feyisa et al., 2007). Therefore, to enhance the productivity of physical structures such as soil bunds and to increase the adoption rate of SWC technologies by the farmers, evaluating the combined effect of soil bund with biological SWC measures is the objective of this paper.

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2. Materials and methods 2.1. Description of the study area The experiment was conducted in the Debre Mewi experimental watershed, located at 118200 1300 N and 378250 5500 E (Fig. 1) which is 30 km south of Bahr Dar city along the road to Mota. Geographically, the watershed belongs to two districts: Yilmana Densa and Bahr Dar Zuria, in West Gojam administrative zone of Amhara Region. It drains to Blue Nile River. It has a unimodal type of rainfall with an average annual of 1240 mm, while the minimum and maximum monthly temperatures are 9.3 8C and 25.7 8C, respectively. June, July and August receive the largest shares of the annual rainfall. The local geology is characterized by volcanic basalt flows and Cenozoic pyroclastic fall deposits (Abiy, 2009). The dominant soil types are nitisol, vertisol, and regosol. Nitisols dominate the upper parts of the watershed and are highly suitable for crop production. Vertisols are widespread in the lower parts of the watershed and are used for growing teff (Eragrostis tef), chick pea (Cicer arietinum) and grass pea (Lathyrus sativus). Regosols occur on the steep and highly eroded parts of the watershed. The watershed suffers from rapidly expanding active gullies (Tebebu et al., 2010), as well as sheet and rill erosion on all cultivated slopes (Zegeye et al., 2010). Cultivated land covers more than 70% of the watershed, and the remaining portion of the watershed is covered with communal grazing areas, bush lands, eucalyptus woodlots. The area is characterized by a small-scale crop and livestock mixed farming system. While it is one of the most productive areas in the country, it also faces a critical shortage of animal feed. 2.2. Design of experimental plots Six different treatments: control (without any treatment), soil bund alone, and soil bund combined with Tephrosia (Tephrosia vogelii), vetiver grass (Vetiveria zizanioides), elephant grass (Pennistum purpureum), and a local grass called sembelet (Hyparrhenia rufa), respectively were evaluated for their effects on soil loss and runoff reduction at 10% slope field. The experimental plots (Fig. 2) were designed according to Herweg and Ostrowski (1997). Each of the treatments was tested on an area of 180 m2, similar to the dimensions of the experimental plots used in the SCRP studies (Adimassu et al., 2012; CDE, 2000). To prevent flood into the plots, a cut-off drain was constructed at the head of the experimental plots. Between plots, sheets of corrugated iron were inserted 10 cm into the ground and protruded 20 cm above the ground to prevent runoff and sediment flow into and from the plot. At the lower end of each plot, two rectangular tanks having a capacity of 0.6 m3 and 0.8 m3 were installed for sediment and runoff collection. The larger tank (Tank 2) was used to collect an overflow from Tank 1 (Fig. 2). The tanks were made of sheets of iron. For each plot, runoff and sediments from the plot were channeled into the first tank through two inlet tubes. Runoff and suspended sediment from over flow of Tank 1 passed through the slot divisor. Ten per cent of the overflow from Tank 1 was collected in Tank 2 while

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T. Amare et al. / Ecohydrology & Hydrobiology 14 (2014) 192–199

Fig. 1. Location of Debre Mewi Watershed in Ethiopia and drainage lines for the watershed.

the remaining 90% of the overflow was spilled out. The total sediment and runoff spilled out from Tank 1 was calculated based on overflow passing through the single slot. After data collection, the water was drained from the two tanks through the emptying tubes. Corrugated iron roofs were used to prevent direct rain water entering into the tanks. The soil bund was constructed with 2% slope to drain excess water into the nearby natural water ways. For all plots, except the control plot, soil bunds were

constructed at 10 m intervals. Potted seedlings of Tephrosia, cuttings of elephant grass, freshly uprooted vetiver grass, and local grasses were planted on the soil bunds in July 2008. Farmers were actively involved in the research process starting from site selection up to the end of the research time through group discussion and frequent field visits (Fig. 3). Farmers’ field days were organized during the third and fourth year of the experiment. Selected farmers from the Debre Mewi and three neighboring watersheds were attended.

Fig. 2. Runoff plot setup-adopted from Herweg and Ostrowski (1997) with minor modifications.

Fig. 3. Farmers and researchers evaluating the performance of biological soil and water conservation measures and soil bund.

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2.3. Data collection and analysis

3. Results and discussion

Runoff and soil loss data were collected whenever there was a runoff generating rainfall in all four rainy seasons. Annual runoff was calculated as the sum of runoff values measured per rainfall event for all rainfall events in the given year. Soil loss was determined for each rainfall event and each plot by measuring the total sediment from Tank 1 and then taking a 0.5 kg sample of fresh slurry and drying it in the oven as a basis for calculating the total dry soil matter per rainfall event from Tank 1. Sediment concentration was determined by taking a 1iter sample from Tank 2 after each rainfall event. After filtering the sample using filter paper, it was dried in the oven and weighed. The total amount of soil loss in the form of suspended sediment per rainfall event was calculated by multiplying the volume of total runoff by the measured sediment concentration. Total soil loss per rainfall event was calculated as the sum of total dry soil in Tank 1 and total suspended sediments. Annual soil loss was determined by adding up all soil loss amounts per rainfall event for all rainfall events in the given year. The amounts of biomass produced for elephant grass and the local grass were recorded. Here, the whole fresh biomass of elephant and local grasses was harvested and weighed at harvesting time. From this biomass, a sample of 1 kg from each grass species was oven dried and weighed to determine the total dry biomass per plot. Tephrosia was pruned when it reached a height of 1 m and incorporated into the soil. Soil samples were collected at a depth of 0–30 cm from each treatment at the end of the experiment to analyze the soil organic matter (SOM). Farmers’ opinion and criteria of selection were used as inputs in technology selection. Data analyses were carried out using excel and SAS 9.2 (SAS Institute, 2008) statistical software. Finally, the experiment has been used as a model to demonstrate SWC to the communities of the study area.

3.1. Soil loss and runoff

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The four-year averages of annual soil loss and runoff ranged from 26 to 71 t ha1 and from 180 to 302 mm, respectively, while the four years annual rainfall ranged from 854 to 1247 mm. This result was obtained from a total of 135 rainfall events (26 in 2008, 23 in 2009, 45 in 2010 and 41 in 2011) that generated runoff. The highest soil loss and runoff values were recorded for the control treatment (with no conservation measures applied), whereas the lowest values were recorded for soil bunds combined with elephant grass, followed by soil bunds combined with Tephrosia (Fig. 4). Looking at the four-year averages, soil bunds combined with elephant grass reduced soil loss and runoff by 63% and 40%, respectively, compared to the untreated control plot. This combined measure also reduced soil loss and runoff by 43% and 28%, respectively, than soil bunds alone. The higher efficiency of elephant grass came from the fact that its growth rate was relatively faster and its denser rooting structure trapped sediment and runoff. Previous studies reported that soil bund alone could reduce soil loss and runoff in the highlands of Ethiopia (Herweg and Ludi, 1999; Ludi, 2004; Hurni et al., 2005; Adimassu et al., 2012). However, this study assured that the efficiency of soil bund was improved when combined with biological measures (Table 1 and Fig. 4). The second most important treatment that showed lower soil and water loss was Tephrosia combined with soil bund. Moreover, the high biomass obtained in short period of time from Tephrosia had additional importance in improving soil fertility in agreement with the findings of Fagerstro¨m et al. (2001), Sileshi et al. (2010), and Bucagua et al. (2013). The performance of vetiver grass against soil erosion is reported by Dalton et al. (1996), Babalola et al. (2007),

Runoff '08

Runoff '09

Runoff '10

Runoff '11

Soil loss '08

Soil loss '09

Soil loss '10

Soil loss '11

140

500 450

120

350

80

300 250

60

200

40

150

Runoff (mm)

Soil loss (t ha-1)

400 100

100 20

50 0

0 Control

SB only

SB + Vetiver SB+Local grass grass

SB+ Tephrosia

SB + Elephant grass

Fig. 4. The annual runoff and soil loss for each of the years from 2008 to 2011 for six treatments consisting of a control and soil bunds (SB) without and with vegetation. Annual rainfall: 854 mm in 2008, 883 mm in 2009, 1102 mm in 2010, and 1247 mm in 2011 study years from 2008 to 2011.

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Table 1 Mean soil loss and runoff for the different treatments (2008–2011). Treatment

Average soil loss (t ha1 year1) *

**

Control Soil bund Soil bund + Tephrosia Soil bund + local grass Soil bund + elephant grass Soil bund + vetiver grass CV (%)

71.3A 46B 30B 31B 26.1B 42.5B 34

– 46A 30BC 31BC 26.1C 42.4AB 25.4

Relative soil loss

100 64.5 42 43.5 36.5 59.6

Runoff (mm)

Relative runoff

*

**

301.7A 249.8B 212.8BC 222B 180.3C 236.1B 10

– 249.8A 212.8AB 222A 180.3B 236.1A 11.6

100 82.8 70.5 73.5 59.7 78

CV stands for coefficient of variation, the relative values (soil loss and runoff) for the control plot are taken as 100%, and values followed by the same letter in a column are statistically insignificant. * refers when all treatments are considered for the analysis and ** refers when only treated plots are considered.

and Oshunsanya (2013). However, this study showed that vetiver grass required at least three years of establishment to conserve soil and water efficiently. Moreover, its biomass production per unit area was smaller as compared to elephant grass so that it was less accepted by farmers. A double mass curve was chosen for graphic representation, with cumulative soil loss on the y-axis and cumulative runoff on the x-axis (Fig. 5). Each dot represents the soil loss and runoff measured after one specific rainfall event. Each graph contains data for all six experimental plots for one year. Shorter lines and lower slopes indicate that soil loss and runoff increase less with rainfall than the lines extending. The shorter the length on both axes, the better the performance in terms of reducing soil loss and runoff. In the first year, the five treatments showed similar slopes and lengths, which can be explained by the fact that the biological material was not yet established well to achieve the intended results. The efficiency difference between untreated and treated plots was observed obviously in Fig. 5. As can be seen the effects of the treatments in the last three years (2009–2011) were highly significant (p < 0.001) for both soil loss and runoff. In all years, the combination of soil bunds with elephant grass showed a better conservation performance than the other treatments. The least significant difference (LSD) for soil loss was higher when all treatments were considered together, as soil loss was much higher from the control plot than from the treated plots; this resulted in a non-significant difference between the treated plots. Excluding the control plot from the calculations led to reduced LSD values, as shown in Table 1, and resulted in a significant difference between the treated plots. For runoff, the result remained the same regardless of whether the control plot was included in the calculations. Despite this considerable reduction in soil loss and runoff, the absolute erosion rates are still very high even on the treated plots, with values between 26 and 46 t ha1 year1 compared to 71 t ha1 year1 for the control plot (Table 1). The average annual soil loss was more than 26 t ha1 for all treatments, which is markedly higher than the tolerable soil loss rate of 10 t ha1 as reported by Mwendera et al. (1997), Morgan (1996) and Tadesse (2001).

attributed to differences in rainfall amount. In 2008, data collection started late, which can partly justify the lower soil loss and runoff rates. Nonetheless, the efficiency trend for soil conservation measures remains similar across the seasons, except for 2008, where the effect was mainly due to the soil bunds only, as the biological measures were not established well yet. Soil bunds combined with elephant grass achieved a significant reduction of soil loss and runoff in all seasons as shown in Fig. 4. 3.3. Intraseasonal sediment concentration trends As shown in Fig. 6, the data for all treatments were plotted for the four years as a function of days after the first runoff. In 2010, there was a big storm in May followed by three weeks of little rain and for that year days after the second runoff events was used as independent variables. Fig. 6 shows the following interesting trends: 1. While storm runoff is generally increasing with progression of the rainfall season (not shown), the concentrations were decreasing for all treatments. Fifty days after the first runoff event concentrations remained generally below 30 g L1 while early in the rainy season average storm concentration of up to 270 g L1 was measured. Ninety days after the first runoff events, the concentration decreased even further to <15 g L1 independent of treatment. 2. For small storms, the sediment concentrations for the control were generally greater than the concentration for the plots with the conservation measures. The reverse was true for the high concentration events (occurring during high runoff events) when several conservation plots had concentrations in excess of the control. Thus conservation practices perform better under low flow condition than high flow conditions. 3. The results of the experimental plots confirm the findings on farmers’ fields of Zegeye et al. (2010) in the same watershed, in which soil loss decreased with the progression of the rainy phase of the monsoon. 3.4. Additional benefits of biological SWC measures

3.2. Temporal variability of soil loss and runoff From the rainy season of 2008 to that of 2011, there was a significant increase in soil loss and runoff, which can be

Additional benefits of biophysical SWC measures were also assessed. An average yield of 2.8 t ha1 year1 of dried forage was obtained from elephant grass on soil bunds.

T. Amare et al. / Ecohydrology & Hydrobiology 14 (2014) 192–199

20

35

2008

197

2009

Soil loss (t/ha)

30 15

25 20

10

15 10

5

5 0 50

0

100

Soil loss (t/ha)

140

150

200

250

0 50

0

100

140

2010

120

120

100

100

80

80

60

60

40

40

20

20

150

200

2011

0

0 400 200 Runoff (mm)

0 Tephrosia

Control

600 Local grass

0

100

200 300 Runoff (mm)

Elephant grass

Soil bund

400

500

Vetiver grass

Fig. 5. Cumulative soil loss and runoff relationships for the different treatments over the four study years from 2008 to 2011.

Sediment concentration, g/L

300

A

Tephrosia Control

250

Local grass Elephant grass

200

Soil bund only Vetiver grass

150

100

50

0 0

20

40

60

80

100

120

140

Days after first runoff

Runoff (mm)

Tephrosia Control

B

50 45 40 35 30 25 20 15 10 5 0

Local grass Elephant grass Soil bund only Vetiver grass

0

20

40

60

80

100

120

140

Days after first runoff Fig. 6. Sediment concentration (A) and runoff trends (B) as a function of days after first runoff event.

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This biomass compensates the land loss by physical SWC structures such as soil bunds as they can occupy up to 8.6% of the crop land (Adimassu et al., 2012). The biomass produced on such physical structures could alleviate the critical shortage of animal feed in the study area. About 90% of the farmers participated in the field evaluation preferred elephant grass to other biological measures due to its high biomass yield that could be used as feed source in addition to its high performance of controlling soil and water loss. This finding may help to encourage the end users (farmers) as an incentive to promote SWC technologies. A group of farmers actively participated in the research directly applied the technology and used it as a model for the rest of the watershed community for the expansion of the research results from plot level to the entire watershed within a short period of time. The local government and developmental agents’ involvement in the research process has played a great role in mobilizing the community to implement the results obtained from this research. Currently, the larger proportion of the watershed has been treated using soil bunds combined with elephant grass. Moreover, the watershed community decided to stop free grazing. Their decision was primarily to protect planted grasses and SWC structures from destruction by livestock. Secondly, farmers perceived that they can benefit more from cut and carry system than free grazing system. The advantage, applicability and sustainability of controlled grazing or cut and carry system were the main issues in the discussion held by farmers, development agents and local administrators with researchers. The lesson gained from this research has been scaled up to other learning watersheds. Soil analysis result for SOM after four years of the experiment showed only a slight difference among and between treatments indicating that the impact of SWC intervention in restoring SOM requires a long-term study. Nevertheless, the SOM content from soil bund combined with Tephrosia was increased by 13% as compared to control plot and still better than other treatments. The importance of Tephrosia to enhance the fertility of the soil was also reported by Fagerstro¨m et al. (2001), Sileshi et al. (2010), and Bucagua et al. (2013). 4. Conclusion The experiment was conducted in northwestern highlands of Ethiopia, where active land degradation is widespread. Physical soil and water conservation (SWC) measures only rarely combined with biological measures have been used on cultivated lands. Generally, combining soil buds with biological measures enhanced the efficiency of soil bund. Among the SWC measures evaluated under this study, soil bunds combined with elephant grass surpassed other treatments for controlling soil and water losses. Its fast growth, establishment habit and high biomass producing capacity satisfied farmers during their evaluation. This finding could be an entry point to make bunds more productive and sustainable. Soil bund combined with Tephrosia was efficient next to elephant grass in reducing soil and water losses. Though soil organic

matter (SOM) restoration requires long years, Tephrosia relatively improved SOM as compared to other treatments. It was very important to involve farmers in the research process because they are the main end users of the research output. Moreover, the farmers have a unique knowledge of the history of erosion and factors that could have triggered its initiation. The involvement of farmers in the research process created interest to implement the best performing SWC measures. Therefore, generating SWC technologies that are technically and economically feasible to apply at farmers’ level is a paramount importance for sustainable agriculture and food security. A group of farmers actively participated in the research process directly implemented the result and used as a demonstration site for the watershed community and finally scaled up to watershed level. Knowing the peak runoff, soil loss, and sediment concentration per unit of runoff occurred during specific rainfall events that are addressed for this study, are critically important to design better SWC strategies. Although there is a significant reduction in soil loss found in this study, it remained above the tolerance limit, calling for further research and development of SWC measures. Conflict of interest None declared. Financial disclosure The research was supported financially by Swiss National Centre of Competence in Research (NCCR) North-South: Research Partnerships for Mitigating Syndromes of Global Change and by the project Sustainable Water Harvesting and Institutional Strengthening of Amhara Region (SWHISA). Acknowledgements This paper is based on the work conducted within the framework of Swiss National Centre of Competence in Research (NCCR) North-South: Research Partnerships for Mitigating Syndromes of Global Change. We also thank Sustainable Water Harvesting and Institutional Strengthening of Amhara Region (SWHISA) for its partial budget support of the study. We thank the Amhara Regional Agricultural Research Institute (ARARI) for all supports and facilitations provided for us. We are grateful to Mohamed Abdela and Anteneh Abewa for their technical assistance. References Abiy, A.Z., 2009. Geological Controls in the Formations and Expansion of Gullies over Hillslope Hydrological Processes in the Highlands of Ethiopia, Northern Blue Nile Region. (Master’s thesis)Cornell University, NY, USA. Adimassu, Z., Mekkonnen, K., Yirga, C., Kessler, A., 2012. Effect of soil bunds on runoff, soil and nutrient losses and crop yield in the central highlands of Ethiopia. Land Degrad. Dev., http://dx.doi.org/10.1002/ ldr.2182. Alemu, G., Bayu, W., Mulatu, Y., 1997. Agroforestry systems in Wello: its importance for feed and fuel wood production and protection of the environment. In: Proceedings of the 4th Technology Generation,

T. Amare et al. / Ecohydrology & Hydrobiology 14 (2014) 192–199 Transfer and Gap Analysis Workshop on Agricultural Research and Technology Transfer, Attempts and Achievements in Northern Ethiopia, Bahr Dar, Ethiopia, March 18–21, 1997, pp. 11–16. Babalola, O., Oshunsanya, S.O., Are, K., 2007. Effects of vetiver grass (Vetiveria nigritana) strips, vetiver grass mulch and an organ mineral fertilizer on soil, water and nutrient losses and maize (Zea mays L.) yields. Soil Till. Res. 96, 6–18, http://dx.doi.org/10.1016/j.still.2007. 02.008. Bojo¨, J., 1996. Analysis of the costs of land degradation in sub-Saharan Africa. Ecol. Econ. 16, 161–173, http://dx.doi.org/10.1016/09218009(95)00087-9. Bucagua, C., Bernard Vanlauweb, B., Giller, K.E., 2013. Managing Tephrosia mulch and fertilizer to enhance coffee productivity on smallholder farms in the Eastern African Highlands. Eur. J. Agron. 48, 19–29, http://dx.doi.org/10.1016/j.eja.2013.02.005. CDE (Center for Development Environment), 2000. Concept and Methodology: Long-Term Monitoring of the Agricultural Environment in Six Research Stations in Ethiopia. Soil Conservation Research Programme. University of Berne, Switzerland. Dalton, P.A., Smith, R.J., Truong, P.N.V., 1996. Vetiver grass hedges for erosion control on a cropped flood plain: hedge hydraulics. Agric. Water Manage. 31 (1–2), 91–104, http://dx.doi.org/10.1016/03783774(95)01230-3. Damtew, E., 2006. Comparative Financial Evaluation of Soil Conservation Measures in North Wello: The Case of Golo River Catchment, Habru Wereda. (Master’s thesis)Alemaya University, Ethiopia. den Biggelaar, C., Lal, R., Wiebe, K., Eswarnan, H., Breneman, V., Reich, P., 2003. The global impact of soil erosion on-productivity: II. Effect on crop yield and production over time. Abstract: Adv. Agron. 81, 49–95, http://dx.doi.org/10.1016/S0065-2113(03)81002-7. Fagerstro¨m, M.H.H., van Noordwijk, M., Phien, T., Vinh, N.C., 2001. Innovations within upland rice-based systems in northern Vietnam with Tephrosia candida as fallow species, hedgerow, or mulch: net returns and farmers’ response. Agric. Ecosyst. Environ. 23–37, http:// dx.doi.org/10.1016/S0167-8809(00)00261-9. Feyisa, T., Amare, T., Silassie, Y.G., Adgo, E., 2007. Adaptability of introduced green manuring plant species for soil fertility replenishment. In: Proceedings of the 1st Annual Regional Conference on Completed Research Activities on Natural Resources Management, Bahr Dar, Ethiopia, August 14–17, 2006, pp. 1–10. Gebremichael, D., Nysen, J., Poesen, J., Dekers, J., Haile, M., Govers, G., Moeyersons, G., 2005. Effectiveness of stone bunds in controlling soil erosion on cropland in the Tigray Highlands, northern Ethiopia. Soil Use Manage. 21, 287–297, http://dx.doi.org/10.1111/j.1475-2743. 2005.tb00401.x. Grimshaw, R.G., 1993. The Role of Vetiver Grass in Sustaining Agricultural Productivity. Asia Technical Department, The World Bank, Washington, DC, USA. Guto, S.N., Pypers, P., Vanlauwe, B., de Ridder, N., Giller, K.E., 2011. Tillage and vegetative barrier effects on soil conservation and short-term economic benefits in the central Kenya highlands. Field Crops Res. 122 (2), 85–94, http://dx.doi.org/10.1016/j.fcr.2011.03.002. Guto, S.N., de Ridder, N., Giller, K.E., Pypers, P., Vanlauwe, B., 2012. Minimum tillage and vegetative barrier effects on crop yields in relation to soil water content in the Central Kenya highlands. Field Crops Res. 132 (14), 129–138, http://dx.doi.org/10.1016/j.fcr.2011. 10.014. Herweg, K., Ludi, E., 1999. The performance of selected soil and water conservation measures – case studies from Ethiopia and Eritrea. Catena 36, 99–114, http://dx.doi.org/10.1016/S0341-8162(99)00004-1. Herweg, K., Ostrowski, M.W., 1997. The Influence of Errors on Erosion Process Analysis. Soil Conservation Research Programme. Research Report 33. University of Berne, Switzerland. Hurni, H., Tato, k., Zeleke, G., 2005. The implications of changes in population, land use, and land management for surface runoff in the Upper Nile Basin area of Ethiopia. Mount. Res. Dev. 25 (2), 147–154, http://dx.doi.org/10.1659/0276-4741(2005)025[0147:TIOCIP]2.0.CO;2. Hurni, H., 1993. Land degradation, famine, and land resource scenarios in Ethiopia. In: Pimentel, D. (Ed.), World Soil Erosion and Conservation. Cambridge Studies in Applied Ecology and Resource Management, pp. 27–61.

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Hurni, H., 1987. Erosion-productivity-conservation systems in Ethiopia. In: Proceedings of the 4th International Soil Conservation Conference, Maracay, Venezuela, pp. 654–674. Jagger, P., Pender, J., 2003. The role of trees for sustainable management of less-favored lands: the case of eucalyptus in Ethiopia. Forest Policy Econ. 5, 83–95, http://dx.doi.org/10.1016/S1389-9341(01)00078-8. Kassie, M., Holden, S., Ko¨hlin, G., Bluffstone, R., 2008. Economics of Soil Conservation Adoption in High-Rainfall Areas of the Ethiopian Highlands. Environment for Development (EfD). Discussion Paper Series, March 2008, EfD DP 08-0908-09. www.rff.org/rff/Documents/EfDDP-08-09.pdf. Kebede, T., Yaekob, T., 2009. Research and development of vetiver (Vetiver zizanioides L.) in Ethiopia.In: Paper Presented at the Vetiver System for Soil and Water Conservation, Environmental Rehabilitations and Protection in Ethiopia. Addis Ababa, March. www.vetiver.com/ ETH_WORKSHOP_09/ETH_A7.pdf. Kru¨ger, H.J., Fantew, B., Gebremichael, Y., Kejela, K., 1997. Inventory of Indigenous Soil and Water Conservation Measures on Selected Sites in the Ethiopian Highlands. Soil Conservation Research Programme. Research Report 34. University of Berne, Switzerland. Ludi, E., 2004. Economic Analysis of Soil Conservation: Case Studies from the Highlands of Amhara Region, Ethiopia. African Studies Series A18. (Ph.D. dissertation)University of Bern, Geographica Bernensia, Bern, Switzerland. Million, T., Kassa, B., 2004. Factors influencing adoption of soil conservation measures in southern Ethiopia: the case of Gununo area. J. Agric. Rural Dev. Trop. Subtrop. 105 (1), 49–62. http://www.jarts.info/ index.php/jarts/article/download/50/44. Morgan, R.P.C., 1996. Soil Erosion and Conservation, 2nd ed. Longman Silsoe College, Cranfield University, UK. Mwendera, E.J., Mohamed Saleem, M.A., Dibabe, A., 1997. The effect of livestock grazing on surface runoff and soil erosion from sloping pasture lands in the Ethiopian Highlands. Aust. J. Exp. Agric. 37, 421–430. Oshunsanya, S.O., 2013. Spacing effects of vetiver grass (Vetiveria nigritana Stapf) hedgerows on soil accumulation and yields of maizecassava intercropping system in southwest Nigeria. Catena 104, 120– 126, http://dx.doi.org/10.1016/j.catena.2012.10.019. SAS Institute, 2008. SAS Software 9.2 Version. SAS Institute Inc., Cary, NC. Sileshi, G., Akinnifesi, F.K., Debusho, L.K., Beedy, T., Ajayi, O.C., Mong’omba, S., 2010. Variation in maize yield gaps with plant nutrient inputs, soil type and climate across sub-Saharan Africa. Field Crops Res. 116, 1–13, http://dx.doi.org/10.1016/j.fcr.2009.11.014. Sutcliffe, J.P., 1995. Soil conservation and land tenure in highland Ethiopia. Ethiop. J. Dev. Res. 17 (1), 62–86. Tadesse, G., 2001. Land degradation: a challenge to Ethiopia. Environ. Manage. 27 (6), 815–824, http://dx.doi.org/10.1007/s002670010190. Tebebu, T.Y., Abiy, A.Z., Zegeye, A.D., Dahlke, H.E., Easton, Z.M., Tilahun, S.A., Collick, A.S., Kidanu, S., Moges, S., Dadgari, F., Steenhuis, T.S., 2010. Surface and subsurface flow effect on permanent gully formation and upland erosion near Lake Tana in the northern Highlands of Ethiopia. Hydrol. Earth Syst. Sci. 14, 2207–2217, http://dx.doi.org/ 10.5194/hess-14-2207-2010. Vancampenhout, K., Nyssen, J., Gebremichael, D., Deckers, J., Poesen, J., Haile, M., Moeyersons, J., 2006. Stone bunds for soil conservation in the northern Ethiopian highlands: impacts on soil fertility and crop yield. Soil Till. Res. 90, 1–15, http://dx.doi.org/10.1016/j.still.2005.08.004. Yitaferu, B., 1998. Soil and water management research in northwestern Ethiopia. In: Proceedings of the 4th Technology Generation, Transfer and Gap Analysis Workshop on Agricultural Research and Technology Transfer, Attempts and Achievements in Northern Ethiopia, Bahr Dar, Ethiopia, March 18–21, 1997, pp. 69–77. Zegeye, A.D., Steenhuis, T.S., Blake, R.W., Kidanu, S., Collick, A.S., Dadgari, F., 2010. Assessment of erosion processes and farmer perception of land conservation in Debre Mewi watershed near Lake Tana, Ethiopia. Ecohydrol. Hydrobiol. 10 (2–4), 297–306, http://dx.doi.org/10.2478/ v10104-011-0013-8. Zewudu, T., Hassen, H., 1998. Forage and pasture research achievements in northwestern Ethiopia. In: Proceedings of the 4th Technology Generation, Transfer and Gap Analysis Workshop on Agricultural Research and Technology Transfer, Attempts and Achievements in Northern Ethiopia, Bahr Dar, Ethiopia, March 18-21, 1997, pp. 62–68.