5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in soil fertility maintenance 5 PERFORMANCE OF FARMLAND TERRACES IN SOIL FERTILITY MAINTENANCE 5.1 Introduction The Ethiopian government has realized that drought incidences are largely related to climate change and land degradation. Thus, the government conducted assessments to properly understand the root causes of the problem. The Ethiopian highland reclamation study was one of the first assessments done to understand the root causes and extent of the problem (FAO 1986). The studies indicated that soil erosion is the major causes of the land degradation. As a result, government implemented SWC measures to reduce erosion-induced land degradation (Hurni 1993; Shiferaw and Holden 1999; Tefera et al. 2002). Since then, various mechanical (bunds, terraces, check dams, cutoff drains and waterways) and biological (homestead and communal tree plantations and exclosures) SWC measures have been implemented in drought-prone areas particularly in the eastern and northern highlands (Herweg and Ludi 1999; Badege 2001; Dubale 2001; Amsalu and de Graaff 2007). Although there have been extensive SWC interventions in recent decades, the practice also exists as indigenous knowledge. The presence of rudimentary and poorly established terraces and lynchets in older aerial photographs of the northern highlands reveals that soil conservation is not a completely new practice (Nyssen et al. 2007). Terracing also has a very long history in few other parts of the country like in the Konso area, which is beloved to be older than 400-years and registered as UNESCO world heritage (Watson and Currey 2009). However, terracing exists in only few areas and in most cases the structures need technical improvement (Nyssen et al., 2007). There are however, controversies on the advantages and disadvantages of farmland terracing. The performance of farmland terracing, particularly with respect to soil fertility maintenance in the highlands in general and the study area in particular, has not been sufficiently investigated. The few studies show that the performance of farmland terracing to sustain soil fertility varies with topography (El-Swaify 1997) and position within a terrace (Gebremichael et al. 2005; Nyssen et al. 2007). Other studies argue that the impacts of terracing can only be seen over a long period of time (El- Swaify 1997; Sonneveld and Keyzer 2003; Vancampenhout et al. 2006). Generally, there is insufficient empirical evidence related to the impact of farmland terracing on 60

Performance of farmland terraces in soil fertility maintenance soil fertility over time and space. Therefore, this chapter analyzed impact of farmland terracing with respect to maintaining soil fertility, and evaluated the variability in performance within a terrace, across terrace age and at different terrain positions. 5.2 Material and methods 5.2.1 Study area The study was conducted in the Maybar Soil Conservation Research Site (MSCRS). This is one of the six sites of the Ethiopian Soil Conservation Research Program (SCRP) established in 1982. The program was conducted by the Ethiopian Ministry of Agriculture (MOA) in cooperation with Berne University, Switzerland (SCRP 2000). The site was selected to represent SWC research in the northeastern highlands of Ethiopia with the aim of testing the suitability and effectiveness of the various SWC measures (Herweg and Ludi 1999; SCRP 2000). It is located in the Lake Maybar watershed in Albiko Wereda/district, South Wello zone of Amhara National Regional State about 17 km southeast of the zonal capital, Desse. The watershed is located between 10°58’ and 11°02’ north latitude and 39°38’ and 39°40’ east longitude covering nearly 450 ha (Figure 5.1). The lake drains to the River Borchenna, in the Awash River basin. The watershed is part of the northeastern mountainous area. Geologically, the area is part of the Tarmaber Megezez formation originating from transitional and alkaline basalt (Tefera et al. 1996). According to the FAO classification system (WRB, 2006), the major soils of the watershed are Phaeozems, Regosols, Leptosols, Gleysols and Fluvisols (Weigel 1986). Cambisols, Phaeozems and Leptosols are found on the lower, middle to upper and steeper slopes, respectively. The area receives about 1120 mm mean annual rainfall that on average falls within five months in the two rainy seasons. The mean annual air temperature is 16°C with coolest and hottest temperatures in November (8°C mean daily minimum) and June (26°C mean daily maximum) months, respectively (SCRP 2000). Due to the bimodal rainfall pattern, the area has two cropping seasons. The shorter rainy season is between April and May and the main rainy season is from end of June to end of September (NMSA 1996; SCRP 2000). 61

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