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Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of exclosure

Performance of exclosure in restoring soil fertility demarcate the three landscape positions. Three points (replicates) were randomly located on the base maps in each landscape position. The slopes of the randomly selected points were taken in consideration to make representative sampling in similar landscape position based on contour line depicted on topographic map. Subsequently, coordinates of the individual sampling points were calculated from the maps and stored in global positioning system (GPS) to help to locate each point on the ground. During sampling, points plotted on the base maps were transferred to the ground with the help of GPS using the coordinate values stored in the GPS. Then, sampling plots measuring 5 m x 4 m were marked on the ground keeping the point transferred from the base map at the center of the plot. The sampling sits and plots were designed to assure maximum possible representativeness for the test (Figure 7.4). Soil samples were collected at 1 m intervals from four sides and from the diagonals of the plots in 15 cm depth using a hand auger. The samples from each auger points in a sampling plot were thoroughly mixed, composited and bagged. Accordingly, 9 samples were collected from each exclosure and the control (open area). A total of 54 composite soil samples were collected from the six sites, i.e., 27 samples from the mild and 27 samples from cool zones. Note: Landscape positions: i.e., UP, MP and LP = upper, middle and lower positions, respectively Figure 7.4 Schematic presentation of exclosure sampling The soil samples were air dried, crushed and sieved (2 mm mesh). Soil texture, pH, electrical conductivity (EC), organic carbon (OC), available phosphorus (av. P), total nitrogen (TN), exchangeable bases, i.e., exchangeable calcium (Ca 2+ ), magnesium (Mg 2+ ), potassium (K + ) and sodium (Na + ) and cation exchange capacity (CEC) were determined. Analysis was done using standard laboratory procedures. Accordingly, soil 106

Performance of exclosure in restoring soil fertility reaction and particle-size distribution were determined using glass electrode and hydrometer, respectively by Van Reeuwijk (2002) methods. Exchangeable bases and CEC were determined by the ammonium acetate method at pH 7 as described by Rowell (1994), OC was determined by the Walkley and Black (1934) method and TN by the Kjeldahl method as described in Black (1965). The Olsen et al. (1954) method was used to determine available P. The analysis was done at the National Soils Testing Laboratory in Addis Ababa, Ethiopia. Vegetation cover survey Tree transects on each site were laid out across the landscape based on the previous soil sampling scheme. Three nested quadrats were positioned along transects at lower, middle and upper landscape positions and used to estimate vegetation cover. At each vegetation estimation point, a 2 m by 2 m quadrat was nested at the center of the 10 m by 10 m quadrat. The main- and sub-quadrats were used to visually estimate canopy and ground cover, respectively. The vegetation cover estimation was done for all exclosure and control (open) sites in three landscape positions (lower, middle and upper slope) in three replicates, resulting in 54 main- and sub-quadrats each. Physical SWC structuers, vegetation types and the dominant tree species were recorded during transect walk. Statistical analysis The soil laboratory data were statistically analyzed by analysis of variance (ANOVA) in SPSS version 17. The differences in soil properties between the different ages, agroecological zones and landscape positions of the exclosures were analyzed using statistical analyses techniques with the aim of inferring the impact of the different factors on soil fertility restoration. A general linear model (univariate) was employed taking soil properties as dependent variables, and ages, agro-ecological zones and landscape positions as fixed factors. The test was first conducted using a nested model, which considers interaction of the factors. The nested model is given as: ijk i j k ��� � � ��� � � ��� � � ����� ijk y � � � � � � � � � � � (7.1) ij where: y ijk = dependent variables (soil physico-chemical properties); � = sample mean; � i = effect of agro-ecological zones; � j = effect of age; � k = effect of 107 ik jk ijk

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