5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in maintaining crop productivity i. As terraces develop to bench terraces, no significant yield differences across the slope of the terrain. However, the tendency of slight yield decrease across the terrain could be attributed to erosion/deposition processes before the measure. This implies that a longer time could be necessary to substantially reduce the impact of erosion on crop production and productivity through terracing. This calls for sitespecific, soil fertility maintaining interventions to reduce the variations. ii. The lowest yield of some crops (i.e., wheat) on the lower terrain position can be attributed to the impact of terracing on crops sensitive to water-logging. Hence, it is advisable to cultivate crops appropriate to the respective terrain positions. iii. The magnitude of the yield gradient within a terrace decrease over time. However, management plans should consider the differences within a terrace to eliminate the yield variations. iv. Generally, most crop yields showed stable condition with age of terraces. There was no change in fertilizer use, and nutrient removal through harvest continued. This indicates that terracing helped to maintain crop production and productivity. However, it can be assumed that terracing alone does not increase productivity. Therefore, terracing should be complemented by fertility improving interventions. 100

Performance of exclosure in restoring soil fertility 7 PERFORMANCE OF EXCLOSURE IN RESTORING SOIL FERTILITY 7.1 Introduction Wello is one of the most severely degraded parts of the Ethiopian highlands (Herweg and Ludi 1999; Tekle 1999). It is densely populated and has rugged topography dominated by hills, mountains, escarpments and gorges (Tekle 1999; CSA 2008). The area is also characterized by low agricultural productivity (Weigel 1986; Herweg and Ludi 1999; SCRP 2000). Cultivation and grazing activities have spread to steep landscapes at the expense of forest and natural vegetation (Tekle 1999). As a consequence, land degradation, particularly erosion and soil quality deterioration, has increased at an alarming rate (Tekle 1999; Descheemaeker et al. 2010). Exclosure is one of the widely employed interventions to rehabilitate degraded lands, restock biodiversity and restore soil fertility (Asefa et al. 2003; Descheemaeker et al. 2006; Mekuria et al. 2007). However, controversial results have been reported on the impact of exclosure in restoring resource bases of degraded lands especially with respect to soil fertility. For example, over 100% dry matter increase (McIntosh et al. 1997), up to 70% topsoil organic carbon (OC) increase (Mekuria et al. 2007) and over 10% topsoil total nitrogen (TN) increase (McIntosh et al. 1997; Mekuria et al. 2007) following exclosure were reported. Conversely, others reported insignificant soil OC and TN change in exclosures (Richter et al. 1999; Eshatu 2004; Kalinina et al. 2009). Moreover, farmers perceive exclosure negatively as it creates competition with grazing land, which forced them to reduce livestock and thereby negatively affect their livelihood (Mekuria et al. 2011). Soil fertility self-restoration on degraded land through exclosure is also affected by various factors such as time, terrain steepness and microclimatic conditions (Fu et al. 2003; Descheemaeker et al. 2009; Mekuria et al. 2011; Kalinina et al. 2009). In spite of the controversies and differences in soil fertility restoration, exclosure has been widely implemented in many parts of the Ethiopian highlands including Wello. Moreover, exclosure interventions followed similar approach and management practices regardless of differences in terrain steepness, agroecological zones and age of the exclosures. Therefore, in this chapter we analyzed the impact of exclosure on soil fertility restoration and examined the restoration rate across different exclosure ages, agro-ecological zones and landscape positions. 101

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