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Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Overall summary and

Overall summary and conclusions agro-ecological zone (climate) on biomass production, vegetation type and organic matter addition and mineralization. Conversely, unlike in other studies, soil properties did not show significant differences across the terrain, which could be due to complemantary effect of mechanical SWC measures with exclosures. The mechanical structures enhance in-situ conservation which protect litter and soil erosion towards the lower landscape position especially in early period of exclosure. An evaluation of the performance of farmland terracing regarding soil fertility and crop yield was conducted in the Maybar soil conservation research site (MSCRS) of the South Wello zone. The fixed MSCRS plots were categorized in four terrain slopes positions (3-5%, 5-8%, 8-15% and 15-30%); composite soil samples were collected from 16 plots representing different terrain positions and three terrace positions. The samples were analyzed for selected physico-chemical properties, and the results were statistically tested using analysis of variance (ANOVA) and compared with 1983 survey data. 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 from 40 fixed plots on three terrace positions (low-, mid- and up-) were statistically analyzed using a mixed linear model in SAS, and multiple pair-wise comparison was done using the Tukey-Kramer adjustment. The SWC measures led to clear biophysical changes such as terrain modification, improvement of soil depth, stability of active gullies and stream banks. Furthermore, farmland terracing helped to maintain soil fertility and crop productivity. Among the topsoil physico-chemical properties statistically tasted pH, EC, exchangeable K + and Na + , OC and texture showed statistically significant differences across the terrain. Soil pH and exchangeable bases increased with decrease in slope. The increases were due to erosion and leaching of soluble salts from the upper slope and accumulation at the down-slope terrain. Terraces received higher organic matter input from the non-arable areas and showed 0.55% (5.5 g/kg) higher soil OC contents in positions located adjacent to these lands on the moderately steep (15 - 30%) slopes. As opposed to other studies, topsoil physico-chemical properties except bulk density showed insignificant differences within a terrace, i.e., no significant topsoil fertility differences. Soil bulk density at the mid- terrace position was 0.4 gm/cm 3 higher than at the other positions. With development of bench terraces, incoming runoff was uniformly distributed within a terrace, which reduced the soil fertility gradient. The 134

Overall summary and conclusions uniform soil aggregate deposition resulted in packing of soil particles, thus the midterrase position had a significantly higher bulk density than the other positions. Although removal of soil nutrients through crop harvest continued, differences in soil nutrients with terrace age were non-significant. This indicates that terracing reduced soil nutrient loss through erosion. However, terracing alone does not improve the soil fertility. The ultimate objective of farmland terracing is to improve and/or maintain crop production and productivity. Similar to the topsoil fertility level, crop production showed non-significant differences across the terrain. However, yields showed a decreasing trend with increase in slope of the terrain. The non-significant yield differences for most crops across the terrain indicate that terracing reduced soil erosion and nutrient translocation thereby reducing yield loss in the erosion zone. The yield gradient tendency across the terrain could be due to the soil erosion that had occurred before terracing, which influenced soil depth, thereby affecting nutrient and water storage capacity. Conversely, yields of all crops except wheat showed significant differences (P � 0.002) within a terrace. The yield decreased from the low-terrace towards the up-terrace positions. On average, the grain yield differences were 0.53 t ha -1 between the low- and up-terrace positions, 0.3 t ha -1 between low- and mid-terrace positions, and 0.24 t ha -1 between mid- and up-terrace positions. Unlike findings in other studies, the crop yield variation in this study could be due to the soil depth gradient, which was in same direction as the yield gradient. The soil depth gradient could in turn influence nutrient and soil-water storage. Terracing was introduced in the area while the common agricultural practices were continued. Fertility improvement measures are at a very low level or not at all, and fallowing has been considerably reduced. Crop yield was almost stable with increasing terrace age. This indicates that terracing reduced soil and nutrient loss through erosion, otherwise yields would have been significantly reduced under the continued production constraints and limited agricultural input use. 9.2 Overall conclusions SWC interventions in general and farmland terracing and exclosure in particular have played a considerable role in maintaining and/or restoring soil fertility, crop production 135

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