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5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of exclosure

Performance of exclosure in restoring soil fertility soil TN (280%) and OC (850%) restoration was observed between 20 and 55 years but then the rate decreased. The strong (r 2 = 0.92) correlation between soil OC and TN indicates that the factor determining the OC also affected the TN. Moreover, OC was positively and significantly correlated with most soil properties (Table 7.4). This confirms that OM addition is a base for soil fertility restoration. For example, soil OC was positively and significantly (P = 0.01) correlated (two tailed Pearson correlation) with TN, clay, CEC, and available P. The positive, significant (P = 0.01) and strong correlation (r 2 = 0.92) between OC and TN indicates that age of exclosure affects both in similar ways. Table 7.4 pH Correlation of the major topsoil properties of the exclosures (H2O) Clay Na K Ca Mg CEC TN. OC Clay 0.048 Na 0.013 0.044 K 0.000 0.247 -0.024 Ca 0.071 -0.026 0.167 -0.120 Mg 0.182 0.098 0.152 0.022 0.516 ** CEC 0.083 -0.005 0.374 ** 0.057 0.511 ** 0.254 TN 0.135 0.335 * 0.134 0.245 0.126 0.291 * 0.395 ** OC 0.147 0.421 ** 0.233 0.292 * 0.137 0.276 * 0.375 ** 0.921 ** Av.P 0.038 0.202 -0.143 0.441 ** -0.146 0.169 0.092 0.422 ** 0.436 ** Note: ** Significant at P = 0.01 level (2-tailed). * Significant at P = 0.05 levels (2-tailed) Values are Pearson Correlation coefficients (r), for n = 54 Generally, age of exclosures had no significant effect on pH, EC and exchangeable bases. Soil pH was only slightly different (�pH = 0.1) between the soil of the exclosures and the open sites, for both pH measured in soil:water and soil:KCl suspensions, i.e., pH[H2O] and pH[KCl], respectively. Age of the exclosure had insignificant effect on soil texture due to the fact that soil texture is an inherent property that depends on parent material and weathering rather than on OM addition. Reduction of soil erosion due to exclosure may not play a significant role in changing soil texture, as the soils are shallow and have a coarse texture. The average available P content of the open sites and 10- and 27-year-old exclosures was 3.9 ppm, 4.1 ppm and 4.7 ppm, respectively, but the differences were insignificant. Generally, the findings in this study are similar to those of other studies where soil fertility restoration due to exclosure was 114

Performance of exclosure in restoring soil fertility rapid at the earlier age and decreased with exclosure age (Richter et al. 1999; Fu et al. 2003; Kalinina et al. 2009). 7.3.3 Exclosure soil fertility restoration variation across agro-ecological zones Climate is one of the soil-forming factors, as rainfall and temperature influence soil formation processes through influencing organic matter input and mineralization (Franzluuebbers et al. 2001; Zhao et al. 2010). Soils of the exclosures in the mild zone had a significantly higher pH than in the cool zone (Table 7.5). Table 7.5 Average topsoil properties of exclosures across agro-ecology Agroecology pH (H2O) pH (KCl) EC (ds/m) 115 TN (%) OC (%) av. P (ppm) Mild 7.6 6.3 0.15 0.27 2.70 7.2 Cool 7.3 5.8 0.10 0.17 1.62 3.2 F -value 5.52 ** 21.92 *** 20.36 *** 20.66 *** 22.08 *** 4.81 ** Agro- Exchangeable bases and CEC (cmol(+)/kg) Particles size distribution (%) ecology Na + K + Ca 2+ Mg 2+ CEC Sand Silt Clay Mild 0.37 0.80 23.03 4.84 37.8 49 30 21 Cool 0.28 0.68 22.54 4.63 34.8 61 23 16 F -value 11.44 ** 0.63 ns 0.88 ns 1.35 ns 11.55 * 26.9 *** 23.3 *** Note: Sample size by agro-ecological zone (n) = 27 and overall sample size (N) = 54, other abbreviations are similar to table 7.3 14.3 *** The EC of the soil was also significantly different where a lower EC was measured in the soils of exclosures in the cool (mean EC of 0.10 ds/m) than in the mild zone (mean EC of 0.15 ds/m). Temperature and precipitation directly influence pedogenic processes thereby influencing pH and EC (Franzluuebbers et al. 2001). Hence, the differences in soil pH and EC in the mild and cool zones could be attributed to the differences in pedogenic processes as result of climate differences rather than to the impact of exclosure. Soils of the exclosures in the two agro-ecological zones also showed significant differences in TN (P < 0.001) and OC (P < 0.001). The soils in the mild zone had a significantly higher TN and OC content than those in the cool zone. Results also indicate that the soils of the mild exclosures had 64% (8.7 g/kg) higher OC and 61% (1.2 g/kg) higher TN content than those in the cool zone (Table 7.6). A comparison

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