5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of exclosure

Performance of exclosure in restoring soil fertility 7.3.2 Variation of soil fertility restoration across age of exclosures This study revealed statistically significant differences in soil fertility status between degraded lands (open site) and 10- and 27-year-old exclosures. Among the different soil properties examined, TN and OC showed statistically significant increases with age of the exclosures while CEC showed only marginal differences. On the other hand, other soil properties did not show statistically significant differences (Table 7.3). Though some soil nutrients did not show statistically significant differences, available P, and exchangeable K + and Mg 2+ showed a similar increasing trend to that of OC and TN. Table 7.3 Average topsoil properties across age of exclosures Age pH pH EC TN OC av. P (H2O) (KCl) (ds/m) (%) (%) (ppm) 27-years 7.4 6.0 0.13 0.28 da 2.52 db 7.7 10-years 7.4 6.0 0.11 0.23 b 2.31 c 4.1 Control 7.5 6.1 0.14 0.16 1.64 3.9 F -value 0.86 ns 0.94 ns 1.26 ns 9.73 *** 5.36 ** 1.82 ns Age Exchangeable bases and CEC (cmol(+)/kg) Particles size distribution (%) CEC Sand Silt Clay 27-years 0.31 0.96 22.43 4.90 36.3 dd 55 26 19 10-years 0.37 0.59 23.31 4.58 37.7 b 58 25 17 Control 0.31 0.66 22.61 4.72 35.0 52 29 19 F -value 2.79 ns 2.18 ns 1.08 ns 1.09 ns 3.06 * 2.29 ns 1.80 ns 2.03 ns Note: The superscripted letters (a, b, c & d) of numbers in the columns indicate that the given soil property difference is significant (a) at P = 0.01, significant (b) at P = 0.05, significant (c) at P = 0.1 and (d) non-significant between mean values of subsequent exclosure age/agro-ecological zone/landscape position (Tukey HSD). For example, in the 4 th column and 1 st row TN = 0.28 da indicates that TN mean of 27-year-old exclosure is non-significantly different to that of the 10-year-old exclosure (d) but differences are significant at P = 0.01 with control (a). F -value is *** significant at P = 0.01, ** significant at P = 0.05, * significant at P = 0.1, and ns nonsignificant EC = electrical conductivity, TN = total nitrogen, OC = organic carbon, av. P = phosphorus (available), CEC = cation exchange capacity, Sample size by age (n) = 18 and overall sample size (N) = 54 Na + K + Ca 2+ Mg 2+ Multiple comparisons (Tukey HSD post hoc tests) between the soils of the three age categories (control, 10- and 27-year-old exclosure) showed that the 27-yearold exclosures had statistically significantly higher TN (P < 0.001) and OC (P = 0.009) contents than soils of the open (control) sites. Likewise, soils of the 10-year-old exclosures also had statistically significantly higher TN (P = 0.045) and OC (P = 0.059) 112

Performance of exclosure in restoring soil fertility contents than the control site where mean differences are significant (Table 7.3). On the other hand, there was no significant OC and TN difference between soils of the 10- and 27-year-old exclosures. Self-restoration of degraded land through exclosures has shown not only vegetation but also soil fertility restoration and carbon sequestration (Tefera et al. 2002; Asefa et al. 2003; Kalinina et al. 2009). The self-restoration processes enhance regular soil OM addition (Kalinina et al. 2009). The differences in OC and TN content were likely due to the differences in OM input as the control sites might have minimal OM input due to continued biomass removal through livestock grazing, woody material collection and soil depletion through erosion (McIntosh et al. 1997; Descheemaeker et al. 2009; Fu et al. 2008). On the other hand, in the exclosures flora regeneration is enhanced, which in turn improves soil OM input (Mekuria et al. 2007; Kalinina et al. 2009; Mekuria et al. 2011). OC restoration rate in the first 10 years was 41% (6.7 g/kg) whereas in the subsequent 10 years it was only 9% (2.1 g/kg). In the early stages, the exclosures were dominated by rapidly recycling annual vegetation like grasses and herbs (Table 7.2). The vegetation dynamics of the current study agree with other reports (Fu et al. 2003; Khater et al. 2003; Asefa et al. 2003; Zhao et al. 2010). Results of a study conducted by Khater et al. (2003) on degraded land in Lebanon indicated that vegetation composition across the recolonization processes follows the order of herbaceous (

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