5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in maintaining crop productivity This indicates that terracing contributed to stable soil fertility (section 5.3.4) and crop yields across time. The stable yield in spite of the continued soil nutrient removal through harvesting, reduced fallowing and no or very limited fertilizer application (chemical and organic) can be attributed to the impact of terracing, which reduced soil erosion. Agricultural practices in Ethiopia in general and in the study area in particular are still traditional. They are characterized by low or no chemical fertilizer utilization, minimal crop residue retention and limited fallowing (Herweg and Ludi 1999; Omiti et al. 1999; Haileslassie et al. 2005). Like other highlands in the country, fallowing is greatly reduced and in some cases completely abandoned. The highlands receive bimodal rainfall, and as a result cultivating land twice a year is common (Hurni 1998; Herweg and Ludi 1999; SCRP 2000). In the study area, limitation of arable land and the food demand for the rapidly growing population has forced farmers to cultivate land twice a year. Thus, fallowing is mostly only between two cropping seasons rather than over years. Therefore, slight yield gradients across the terraces age indicate that terracing has contributed to sustainable production by preventing erosion, which would have resulted in severe degradation and yield loss. Discussions with the local farmers confirmed this. The farmers reported that before terracing considerable farmland on the very steep slopes was abandoned as the land became unproductive. This land was then terraced, fallowed for some time and then used for crop production. This clearly shows that terracing positively impacted crop production. The stable crop yield despite the continued nutrient removal through crop and residue harvest (Omiti et al. 1999; Haileslassie et al. 2005) also indicates that terracing played important role and that otherwise yields could have significantly decreased. It can be concluded that terracing has helped to achieve sustainable production; however terracing alone may not improve agricultural productivity. 6.4 Summary and conclusions This study analyzed the performance of terracing with respect to crop productivity, and evaluated the yield differences across the slope of the terrain, within a terrace and across terrace age. Yield data (grain and biomass) of seven crop types, namely barley, maize, wheat, emmer wheat, teff, horse bean and field pea collected between 1995 and 2009 98

Performance of farmland terraces in maintaining crop productivity from 40 fixed plots on three terrace positions (low-, mid- and up-) were evaluated. The plots were grouped based on DEM-generated slope classes as gently sloping (3-5%), sloping (5 - 8%), strongly sloping (8 - 15%) and moderately steep (15-30%). The data were statistically analyzed in SAS taking grain and biomass yield as dependent variables; slope of the terrain and terrace position as fixed factors, year as covariate, and plot as a subject effect. Generally, yield (biomass and grain) showed insignificant differences across the terrain with a tendency to decrease with slope increase. Nevertheless, few crops showed marked differences. For example, barley yield significantly decreased with slope increase, while field pea showed higher yields on the sloping terrain position. The insignificant yield differences for most crops across the terrain imply that terracing reduced soil erosion and nutrient translocation, thereby reducing significant yield loss in erosion zone. The tendency of yield decrease across the terrain could be due to the soil erosion before terracing that influenced soil depth, thereby affecting nutrient and water storage capacity. The effect of previous erosion depends on the crop type (Calvi�o and Sadras 1999; Tesfaye and Walker 2004). On the other hand, biomass and grain yield of all crops except wheat significantly decreased from low-terrace position towards up-terrace position. This is in line with other studies (Herweg and Ludi 1999; Dercon et al. 2003; Vancampenhout et al. 2006; Nyssen et al. 2007). The studies relate the differences to topsoil fertility gradients however, in this study there were no such variations (Chapter 5). Thus, the variation could be due to the soil depth gradient that in turn influenced nutrient and soilwater storage. Crop production in the study area applies only limited fertility improvement measures, and fallowing is reduced. This indicates that terracing reduced soil and nutrient loss through erosion, otherwise yields would have been significantly reduced under the continued nutrient export through harvest. The only slight yield change after terracing indicates that terracing alone does not improve soil fertility and thereby crop production. Thus, farmland terracing should be supplemented by other agricultural packages such as use of soil fertility amendments and other agronomic practices. In this study the following is concluded: 99

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