5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Implications of soil and

Implications of soil and water conservation measures for land rehabilitation- a synthesis indicates that the area has livestock feed problems, which calls for alternative forage production. At an early stage, exclosures are mainly covered by grasses that are used as livestock feed. However, the grasses are gradually replaced by unpalatable species and higher layer vegetation (Angassa and Oba 2008; Zhao et al. 2010). This leads to an increased livestock feed problem. Studies conducted in the Borana area (southern Ethiopia) showed that exclosure and banning of traditional rangeland fires resulted in bush encroachment that radically altered the pasture quality and productivity. Therefore, failure of developing alternatives that optimize current and future demands could lead to further degradation (Oba et al. 2000; Angassa and Oba 2008). Gradual replacement of palatable species and shortage of livestock feed could lead to further dependency on crop residues and an increased pressure on the limited pastures lands and open areas. This could result in severe degradation in these areas. Therefore, we recommend that exclosures should be planned and implemented in a way that considers resources conservation as well as sustainable long- and short-term benefits to the community. Exclosure use and management should be planned with defined purposes such as soil conservation (reduced soil erosion), flood and landslide control, forage production, biodiversity conservation, apiculture and other multipurpose. Planning also needs to include detailed management on how and when each activity should take place rather than taking corrective action. During the field study, it was observed that most exclosures have neither management nor utilization plans. This calls for strategic correction. Otherwise there will be a reduction in animal feed supply from exclosures, as they will become dominated by higher layer vegetation. There will also be further degradation of open areas and arable lands due to overgrazing and crop residue use as livestock feed would continue. 8.5 Implications of farmland terracing for soil fertility and crop yield This study revealed that topsoil fertility gradients within a terrace did not exist, which is associated with the development of bench terraces. Sediment deposition and/or erosion gradients within a terrace are mostly minimized. Thus, the topsoil receives uniform runoff that adds/removes equal volumes of sediment within a terrace, as the slope variation low- and up-terrace is greatly reduced. Topsoil fertility restoration also 126

Implications of soil and water conservation measures for land rehabilitation- a synthesis showed insignificant differences across the terrain (Chapter 5). This indicates that terracing reduced soil erosion from upper to down-slope positions. The lack of topsoil fertility variation across the terrain also indicates that terracing reduced erosion and deposition processes. As soil erosion before terracing was severe (Hurni 1993), topsoil fertility stability in the presence of continued soil nutrient export through crop harvest and minimal fertilizer (organic and inorganic) use indicates that terracing played an appreciable role at least in maintaining the topsoil fertility status. Therefore, terracing reduced soil erosion and nutrient loss due to erosion. The results of the crop yield analysis agreed with those on the impact on soil fertility through terracing. Crop yield showed only very slight changes with time, which indicates that terracing, helped to maintain production (Chapter 6). Crop yield (biomass and grain) also showed only slight changes across the terrain. The slight yield reduction from the lower to upper slope of the terrain could be a result of erosion before the terracing (Chapter 6). This indicates that terracing contributed positively to crop production stability. However, terracing negatively affected the productivity of crops sensitive to water logging such as wheat, and this led to yield gradients within the terraces. Yields of almost all crops showed significant differences within a terrace, where higher values were observed above the terrace riser. The yield gradient within a terrace could be attributed to soil depth, which resulted in differences in the soil water and nutrient storage capacity. Grasses grown on terraces stabilize the structures and are also used as additional sources of livestock feed as long as the cut-and-carry system is used. Therefore, terracing maintained agricultural productivity and reduced erosion-induced land degradation. However, in order to improve productivity, nutrient depletion due to crop harvesting and other losses should be compensated through input use. 8.6 Implications of SWC-driven LULC change for resource restoration Widespread efforts have been made to implement SWC measures in the past three decades with the aim of reversing land degradation. The measures, particularly exclosures, helped to restore the vegetation cover of marginal lands, especially on mountains and hillsides. Currently, the Wello area is largely covered by exclosures (Chapter 4). The MODIS data analysis revealed that the area covered by 127

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