5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in soil fertility maintenance differences. This analysis clearly demonstrates that terracing reduced soil loss through water erosion, and consequently erosion and deposition processes led to changes in soil bulk density, i.e., caused compaction particularly at the mid-terrace position. Table 5.5 Soil properties in 1983 and 2010 at the study site Mean value Mean value Difference Soil property (1983) (2010) (2010 – 1983) pH [H2O] 6.44 6.71 0.27 DB (gm/cm3) 1.02 1.35 0.33 OC (%) 1.98 1.58 -0.4 TN (%) 0.16 0.19 0.03 Na+ (cmol (+)/kg) 0.18 0.31 0.13 K+ (cmol (+)/kg) 0.64 0.49 -0.15 Ca2+ (cmol (+)/kg) 34.19 23.84 -10.35 Mg2+ (cmol (+)/kg) 11.58 5.26 -6.01 av. P (ppm) 17.27 12.11 -5.16 Source: Soil survey report of MSCRS (Weigel, 1986) The SWC interventions lead to reduced soil and nutrient loss through erosion (Hurni 1993; Haileslassie et al. 2005; Vancampenhout et al. 2006). In the study area, interventions for maintaining soil fertility such as use of organic and inorganic fertilizer and practices that enhance nutrient recycling are still much below the existing nutrient depletion rate. In the MSCRS and most parts of the Ethiopian highlands both grain and residue are harvested. The crop residue is used as livestock feed, and animal dung is used for household energy and not returned to the farmlands. Moreover, traditional fallowing is currently hardly practiced, and farmlands are cultivated two times a year with very low or no fertilizer use. The SWC structures are also not completely sediment proof, and the effectiveness of the structures varies with slope and structure type. For example, Herweg and Ludi (1999) reported 0.5 t ha -1 to 3.3 t ha -1 annual soil loss under different SWC structures at the MSCRS. All the above processes facilitate soil nutrient export out of the system, which in turn influence the measured soil fertility states of the terraces over time. The performance of the SWC structures depends on not only appropriate design and construction quality of the structures but also on their suitability for specific site conditions. It was reported that level structures have better performance, while graded structures induce higher soil loss than cultivation without SWC (Herweg and 80

Performance of farmland terraces in soil fertility maintenance Ludi 1999). On the other hand, level structures particularly at lower terrain positions are prone to water logging, while graded structures have no such problems (Herweg and Ludi 1999). As discussed above, among the different cause of soil nutrient loss, farmland terracing impacts only on soil and soil nutrient loss through erosion, while other factors still continue to remove soil nutrients. However, with the development of level structures, soil loss through water erosion was considerably reduced (Gebremichael et al. 2005; Herweg and Ludi 1999). Generally, soil nutrient loss was small while some gain was also evident. The analysis indicates that farmland terracing plays an important role not only in reducing physical soil loss but also in retaining the nutrients. The negative soil nutrient balance could be due to the continued nutrient removal through crop harvest and also partly by soil erosion, as it is difficult to completely stop erosion through terracing (Herweg and Ludi 1999). Without terraces, the soil nutrient status would not be as measured in this study with the continued traditional cultivation practices. 5.4 Summary and conclusions Terracing is one of the most widely adopted practices. Despite various controversies on the merits and performance of terracing, inadequate empirical evidence exists concerning the role of terracing on soil fertility. The purpose of this study was to analyze impact of farmland terracing in maintaining soil fertility and evaluated variability in its performance within a terrace, across terrace age and at different terrain position. The study was conducted in MSCRS. A total of 48 composite soil samples were collected from 16 plots representing four terrain slope categories (3-5%, 5-8%, 8- 15% and 15-30%), three positions within a terrace and each in four replicates. The soil samples were analyzed for texture, pH, EC, OC, av. P, TN, exchangeable bases, CEC and bulk density while soil survey data of 1983 (Weigel 1986) were used as baseline data. The soil laboratory results were statistically tested using analysis of variance (ANOVA). The results reveal that SWC measures led to clear biophysical changes such as terrain modification, improvement of soil depth, stability of active gullies and stream banks and development of bench terraces. Soil properties such as pH, EC, OC, CEC, Na + , K + and texture showed statistically significant differences across slope of the 81

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