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5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of farmland

Performance of farmland terraces in maintaining crop productivity Note: Terraces positions: A = low-, B = mid- and C = up-terrace position Figure 6.3 continued 6.3.3 Impact of terracing on crop yield across terrace age In this analysis, in order to avoid the effect of yield variation on the overall crop yield, the comparison is based on relative yield. The relative yield for each measurement was calculated as: relative yield = [grain yield/biomass yield]*100 (Hay 1995). The relative yield of all crops measured in all plots in every year under consideration is termed as ‘all crops observed relative yield’. The analysis revealed very high variations ranging from 4% for field pea to 83% for wheat (Figure 6.4b). On the other hand, the average values of all crops for each year were almost stable with only a very slight increase (Figure 6.4b), which varied from 32% in 1998 to 49% in 2009 (Figure 6.4b). The maximum and minimum mean relative yield of all crops showed wide variation (Table 6.4). Accordingly, the yearly minimum values ranged from 4% to 21%, while the maximum values were from 63% to 77% (Table 6.4). The analysis showed high fluctuations across the year without a regular trend. As a whole, the yields tended to increase slightly with terrace age (Figure 6.4). This shows that grain and biomass yield across age of the terraces followed a nonlinear trend with very high standard deviations (Figure 6.4a). The irregular yield change could be due to other factors such as rainfall 94

Performance of farmland terraces in maintaining crop productivity variability rather than to the influence of terracing on plant nutrition (Hay 1995). For example, in 1998, an abrupt yield decrease was observed. Table 6.4 All crops minimum, maximum and mean relative yield over time (%) Year 1995 1996 1997 1998 1999 2000 2001 Max. 73 64 68 50 83 77 77 Min. 4 7 12 11 21 10 21 Mean 46 41 44 32 46 38 48 Year 2003 2004 2005 2006 2007 2008 2009 Max. 70 67 63 67 67 65 73 Min. 6 22 22 22 18 7 18 Mean 47 45 45 45 46 42 49 Figure 6.4 Relative yields across terrace age: (a) All crops observed relative yield, and (b) All crops mean relative yield 95

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