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5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in soil fertility maintenance Table 5.2 Average (n = 12) soil properties in 0-20 cm depth on terraces across slope of the terrain Slope pH pH EC TN OC av. P CEC (%) 3-5 (H2O) 7.0 (KCl) (ds/m) (%) (%) (ppm) (cmol(+)/kg) daa 5.3 baa 0.10 bdb 0.18 1.45 ddb 15.2 42.5 dbd 5-8 6.9 aa 5.1 ad 0.07 dd 0.18 1.42 db 10.4 43.3 bd 8-15 6.4 d 4.8 b 0.08 d 0.18 1.47 b 6.8 46.8 b 15-30 6.5 5.0 0.07 0.21 1.97 16.1 42.3 F -value 22.50 *** 22.57 *** 4.62 ** 1.30 ns 4.56 ** 2.04 ns 5.81 ** Slope Exchangeable bases (cmol(+)/kg) Db (%) (g/cm 3 Particles size distribution (%) Na ) + K + Ca 2+ Mg 2+ Sand Silt Clay 3-5 0.40 dcb 0.54 ddd 24.2 5.12 1.35 19 dbb 36 bdd 45 dbb 5-8 0.36 dd 0.69 bb 23.7 5.53 1.33 18 bb 40 cb 42 dd 8-15 0.24 d 0.36 d 24.7 5.50 1.32 28 d 36 d 36 d 15-30 0.22 0.38 22.8 4.90 1.41 27 36 37 F -value 3.43 ** 6.52 *** 1.66 ns 1.04 ns 0.39 ns 6.94 *** 4.53 ** 5.18 ** Note: The superscripted letters (a, b, c, d) indicate that soil properties of a given slope range are different (a) at P = 0.01, (b) at P = 0.05, (c) at P = 0.1 and (d) non-significantly different from the subsequent slope ranges (Tukey HSD). For example, in the 1 st column and 1 st row pH (H2O) = 7.0 daa indicates that soil pH (H2O) differences on terraces located at 3-5% slope terrain is non-significantly different than that of the 5-8% slope (d). But the soil pH (H2O) on terraces located at 3-5% slope terrain was statistically significantly higher than that of the 8-15% slope (a) at P = 0.01 level and also significantly higher than that of the 15-30% slope terrain (a) at P = 0.01 level. F-value is *** significant at P = 0.01, ** significant at P = 0.05 level, * significant at P = 0.1 level, and ns non-significant EC = electrical conductivity, TN = total nitrogen, OC = organic carbon, av. P = phosphorus (available), CEC = cation exchange capacity, Db = bulk density The statistical analysis revealed that the soils of the farmland terraces had statistically significantly different CEC (P = 0.002), exchangeable Na + (P = 0.027) and K + (P = 0.001) content across the terrain (Table 5.2). On the other hand, exchangeable Ca 2+ and Mg 2+ did not show statistically significant differences with slope change. Generally, contents of soil exchangeable bases were low and showed a decreasing trend with slope increase (Figure 5.6). For example, exchangeable K + ranged from 0.1 cmol (+)/kg to 1.27 cmol (+)/kg with an average of 0.49 cmol (+)/kg. The highest exchangeable K + level measured in the topsoil of the study area was 1.27 cmol (+)/kg, which is equivalent to 0.45 kg K + t -1 soil. This indicates that the soils have a low exchangeable K + level (Alexander 1991; Bergmann 1992; Sys et al. 1993). Soils on the 5-8% slopes had statistically significantly higher (P � 0.005) exchangeable K + than on the 8-30% slope. However, differences in exchangeable K + (�K + � 0.12 kg K + t -1 soil) 70

Performance of farmland terraces in soil fertility maintenance between terraces on gentle and steep slopes were too low to cause relevant fertility differences. In contrast, CEC showed an irregular trend across the slope of the land. Indepth comparison indicated that soils of the terraces on 8-15% slopes had statistically significantly higher CEC (P < 0.05) than those on the other slope. Soil CEC of the terraces across slope of the terrain ranged from 42.3 cmol (+)/kg to 46.8 cmol (+)/kg. Figure 5.6 Soil exchangeable bases on terraces across the terrain The differences in contents of exchangeable bases within a given watershed could depend on variation in parent material or micro-climate and/or erosion (Chen et al. 1997; Olarieta et al. 2008). Since Lake Maybar watershed has a uniform geology (basalt) and micro-climate; neither geology nor micro-climate contributed to the exchangeable bases (K + and Na + ) differences across the slope of the terrain. Statistically significant differences in the values between terraces of different terrain position could be attributed to erosion, deposition and leaching processes. Erosion and leaching remove soluble salts from upper-slope and accumulate these at the down-slope positions (Pimentel et al. 1995). Pimentel et al. (1995) reported that soil transported through erosion could contain a threefold higher nutrient amount than soils remaining behind. 71

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