Soil available potassium and magnesium and oak dieback in acid soils from middle Belgium.
1993
Vasic M. | Herbauts J. | Tanghe M.
Available cations (calcium, magnesium, potassium), total carbon and total nitrogen were determined in the hemiorganic horizon and upper 20 cm soil layer for ten pairs of Quercus robur L. in three stands of the 'Foret de Soignes' (Belgium). Each pair is composed of one health and one strongly declining tree. Five pairs were also sampled from foliar analysis and soil Bt analysis. Results show that potassium and magnesium levels as well as the magnesium/calcium and potassium/calcium ratios are significantly lower under declining trees. Foliar analysis show a general decrease of the mineral content of the leaves of declining trees (including the calcium content), but this could possibly mean that the recommended sampling period for oak (last three weeks of August) is too late for strongly declining trees. It seems that low exchangeable potassium and magnesium levels, associated with high calcium content in the upper layers of soil, might be partly responsible for the oak decline. Nevertheless, the slightness of the differences in mean values suggests that these levels should only be considered as predisposing or aggravating factors, or that they may be correlated with a decisive unidentified factor.
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