5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in soil fertility maintenance the study plan. Accordingly, the topsoil analysis results reported by Weigel (1986) were averaged and used for the comparison. Since the baseline data did not fully match with the current sampling design, the terrace-age effect on soil fertility was not statistically analyzed. 5.2.4 Statistical data analysis The soil laboratory data were statistically tested by analysis of variance (ANOVA) in SPSS version 17. A general linear model (univariate) was used taking soil analysis data as dependent variables and the slope of the land and positions within the terrace as fixed factors. The model is given as: ij i j ��� �ij ij y � � � � � � � �� (5.1) Where y ij = dependent variable (soil physico-chemical properties), � = sample mean, � i = effect of slope, � j = effect of terrace position, ��� �ij = effect of slope and terrace position interaction, and � ij = random error The model was evaluated by the likelihood-ratio test to decide whether to retain or reject interaction of fixed factors in the model. The test revealed that the full model, which considers interaction of factors, had higher values. This indicates that the observed outcome was more likely to occur under the full than under the reduced model, thus the full model was retained. In order to test the correlation of the different soil properties, a bivariate correlation analysis was done in SPSS version 17. 5.3 Results and discussion 5.3.1 Biophysical changes after farmland terracing The field observations revealed that SWC measures have been widely implemented in Wello and most of the structures are stabilized. Stability of SWC structures depend on various factors such as slope of the land, construction quality, construction material, support of physical structures by biological measures, and appropriateness of structure to the site conditions (El-Swaify 1997; Zhang et al. 2004; Olarieta et al. 2008). For example, appropriateness of SWC structures with increasing slope comes in the order of soil bund, stone-faced bund, stone terrace, bench terrace and hillside terrace, respectively (Cao et al. 2007; Nyssen et al. 2007). Most of the terraces in the study site 66

Performance of farmland terraces in soil fertility maintenance have become bench terraces, and grasses growing on the terraces also stabilized the structures. Measurements to estimate the slope gradient between the edges of terraces (low- and up-terraces walls) indicated nearly level conditions, mostly

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