Effects of cultivating black locust (Robinia pseudoacacia L) on soil chemical properties in Hungary

Quelle: Forstarchiv 80: 6, 307-313 (2009)

Abstract: Due to its symbiotic N2 fixation, black locust (Robinia pseudoacacia L.) may improve the N and C status of soils. On the other hand it may also cause losses of cations and acidification through enhanced proton production by nitrification and leaching The humus layer and the mineral soil to a depth of 50 cm at four different forest sites in Hungary dominated by Robinia were studied for their chemical properties in comparison with those under adjacent planted oak stands (Quercus cerris L. and Quer-cus pubescensNd.). Elevated biomass accumulation resulted in significantly higher C, N, P and S contents of the forest floor under Robinia. A significant decrease in soil pH under black locust stands compared to oak stands was detected in the mineral soil. Higher proton concentrations as well as lower Mg2+ concentrations under black locust stands confirmed the hypothesis of nutrient depletion and acidification by cultivation of this tree legume. However, due to high variation of inventory data at the landscape level, the effects of black locust cultivation on soil chemical properties were less pronounced. In contrast, a comparison of several paired stands of locust and oak under comparable soil chemical environments showed that the spatia heterogeneity in soil properties was reduced. In addition, processes of soil degradation through black locust forests became more distinct. Another important aspect influencing the magnitude of soil degradation by N fixing trees is the continued cultivation at the same place. Soils under Robinia stands of the second generation showed significantly higher concentrations of H+ and Al3+than those of the first generation forests. The impact of longer Robinia cultivation resulted in 70% higher Al3+ concentrations in soils of the second tree generation. Moreover, acid-indicating H+ concentrations were approximately 100% higher, and Fe3+ concentrations were 350% higher under second generation Robinia. In spite of the observed changes in the chemical status of the Hungarian soils under Robinia, we do not expect severe reductions in tree growth caused by acidification and nutrient losses, even after repeated cultivation on the same site. However, sites with lower base saturation may suffer more under nutrient depletion caused by N fixation of Robinia. This possibility should be taken into account when considering the introduction of Robinia pseudoacacia as an alternative tree species with high growth rates even on nutrient poor soils

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