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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 based on age and agro-ecological zone shows that soils of the mild exclosures had a higher average OC content than soils in the corresponding age exclosures at cool zone except for some deviation in the 10-year-old exclosure (Figure 7.7). However, the average TN was higher than in the corresponding age exclosure in the cool zone. Figure 7.7 Soil OC (a) and TN (b) contents of exclosures across age and agroecological zones Table 7.6 Soil OC and TN content in exclosures across age and agro-ecological zones Mean TN content (%) Mean OC content (%) Agro-ecology Agro-ecology No Exclosure age Mild Cool Mild Cool A Control 0.19 0.13 2.16 1.12 B 10 years 0.28 0.18 2.66 1.95 C 27 years 0.35 0.21 2.16 1.12 Average of B and C (%) 0.31 0.19 2.41 1.53 Average of B and C (g/kg) 3.15 1.92 24.10 15.35 The soils of the exclosures in the mild zone also had statistically significantly higher available P than those in the cool zone. The major sources of P are mineral elements. However, the C/P ratio, which reflects organic P release through OM mineralization, did not differ. This could imply that the available P differences were unlikely due to the OM input differences. The lower available P in the cool zone could be due to higher P fixation. The differences in available P between the two zones could be due to differences in the pedogenic process and not to the influence of climate on OM. 116

Performance of exclosure in restoring soil fertility Exchangeable bases except Na + were not significantly different between agroecological zones. In contrast to the exchangeable bases, the CEC significantly (P = 0.002) varied between agro-ecological zones. Like OC, TN and most other soil properties, a higher CEC was measured in the soils in the mild (37.8 cmol (+)/kg) than in the cool zone (34.8 cmol (+)/kg). The CEC of soil is determined by the two colloidal particles clay and humus (Oorts et al. 2003). The CEC correlated positively and significantly (P = 0.01) but not so strongly (r 2 = 0.375) with OC. This indicates dependency of the CEC on OM. The agro-ecological zone showed statistically significant soil texture differences. Soils in the mild zone exclosures had 5% higher clay and 7% higher silt than the soils in the cool zone. 7.3.4 Exclosures soil fertility restoration variation across landscape The results of the present study reveal that landscape position of the exclosure did not show significant differences in most soil properties such as EC, TN, OC, exchangeable bases (Na + , K + , Ca 2+ and Mg 2+ ), CEC and texture (Table 7.7). Only available P showed statistically significant differences across landscape position of the exclosures. It significantly increased (P = 0.05) towards the upper landscape positions in contrast to the direction of the soil erosion and deposition process. On average, available P was 3.4 ppm at the lower, 3.8 ppm at the middle and 8.5 ppm at the upper landscape positions of the exclosures. Table 7.7 Average topsoil properties across landscape position of exclosures landscape position pH (H2O) pH (KCl) EC (ds/m) 117 TN (%) OC (%) av. P (ppm) LP 7.4 6.0 0.12 0.19 1.94 3.4 dc MP 7.5 6.1 0.12 0.25 2.39 3.8 c UP 7.4 6.0 0.13 0.23 2.14 8.5 F -value 0.77 ns 0.57 ns 0.29 ns 1.94 ns 1.30 ns landscape position 3.26 ** Exchangeable bases and CEC (cmol(+)/kg) Particles size distribution (%) Na + K + Ca 2+ Mg 2+ CEC Sand Silt Clay LP 0.32 0.63 22.92 4.71 35.92 55 27 18 MP 0.33 0.62 23.15 4.86 36.19 55 27 18 UP 0.34 0.97 22.28 4.63 36.84 55 26 19 F -value 0.37 ns 2.23 ns 1.01 ns 0.59 ns 0.38 ns 0.04 ns 0.07 ns 0.02 ns Note: Landscape position, i.e., LP = lower position, MP = middle position, and UP = upper position Sample size by landscape position (n) = 18 and total sample size (N) = 54, other abbreviations are same as table 7.3

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