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5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in soil fertility maintenance over 120 cm soil depth at low-terrace positions and the remaining 20% a minimum of 80 cm depth, while in the 1983 survey soil depths of less than 120 cm were found in less than 50% of the profiles. Active gullies and stream banks (Figure 5.5a and c) existing at the start of the MSCRS project were well stabilized and covered by vegetation at the time of the study (Figure 5.5 b and d). There have also been marked terrain modifications and biophysical changes (Figure 5.4 and Figure 5.5). The presence of non-angular and different-size (very fine to medium) gravels in the soil profile indicates erosion and deposition processes within the watershed. The gravel volume and diameter change with the general slope of the land reveal the deposition patterns across the landscape. Coarser material was found in terraces adjacent to river courses and on upslope positions, while fine-textured soils were found in the down-slope positions. (a) Active gully (source MSCRS, 1983) (b) Stabilized gully (June 2010) (c) Stream bank (source MSCRS, 1983) (d) Stablized stream bank (June 2010) Figure 5.5 Gully and stream bank before (1983) and after (2010) SWC interventions in Lake Maybar watershed 68

Performance of farmland terraces in soil fertility maintenance 5.3.2 Soil fertility variation on farmland terraces across the terrain Terracing modifies terrain conditions by changing slope angle and length. Consequently, terracing influences soil properties by changing soil erosion and deposition processes. Accordingly, soil properties were significantly different across the slope of the terrain. Soil pH is the first parameter to be considered in soil fertility evaluation, while EC is important to determine the salinity level. Generally, the pH values were nearly neutral with a mean pH [H2O] of 6.7. Values on the farmland terraces significantly (P < 0.001) decreased with increase in slope of the terrain. Multiple comparisons (Tukey HSD test) showed that the terraces in the lower slope positions had statistically significantly higher soil pH than those in the upper slope positions. For example, the terraces on gently sloping and moderately steep terrain had soil pH [H2O] of 7.0 and 6.5, respectively. However, the pH differences between terraces on moderately steep and gentle sloping terrain were small (�pH [H2O] � 0.6). The change in soil pH in both solutions (pH [H2O] and pH [KCl]) showed a similar trend across the landscape and between terraces of successive slope categories (Table 5.2). Soils showed higher acidity on the 8-30% slope than on the 3-8% slopes. But the pH differences between different slopes were too small to cause differences in plant nutrition status and heavy metals toxicity (Dong et al. 1995; Xu et al. 2006). Similarly, soils of the terraces located on different slopes showed statistically significant EC differences. Soils of the terraces on gently sloping (3-5%) land had statistically significantly higher (P = 0.008) EC than those on the terraces on moderately steep slope (15-30%). However, the differences were very small, and values were too low (mean EC of 0.08 ds/m) for adverse effects on the plants (Barbiéro et al. 2001). Due to topographic influences, exchangeable bases could be leached down the soil profile or washed out through runoff; as a result soil pH decreased toward the upslope terrain positions. 69

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