Evolution of the mineral fertility of an acidic soil during a period of ten years in the Vosges mountains (France). Impact of humus mineralisation

Abstract

-A very acidic soil under an adult spruce (Picea abies) stand, in the Basses-Vosges (North-eastern France), was analysed in 1986, and ten years later in 1996. The chemical composition of the mineral horizons did not show much variation, but the sum of exchangeable Ca and Mg in the mineral horizons and their total contents in the OL, OF and OH horizons decreased significantly. In ten years, the Mg in particular had decreased by about 30 kg·ha -1 , i.e. about 1.7% per year of the exchangeable Mg present in 1986. This decrease, which is worrying for the future, may be explained by peaks of humus mineralisation during warm summers combined with the inability of the mineral horizons, highly saturated in aluminium, to retain Ca and Mg coming from this mineralisation in the organic horizons. As a result, these elements were lost in drainage water instead of being taken up by the roots. As this soil was poor in weatherable minerals, the loss could not be compensated for by mineral decomposition. It is probable that a similar situation occurs at the end of a forest rotation when organic horizons are exposed to light and heat. Thus, the degradation of the humus from mull to dysmoder, followed by mineralisation, together with a high exchangeable Al content in mineral horizons and acid rain, all lead to losses of Mg and secondarily Ca at different stages of development of forest stands on acidic soils. Thus humus mineralisation, combined with a high exchangeable Al content, is one of the key mechanisms of soil acidification and impoverishment.aluminium / chemical fertility / climate / humus / soil acidification Résumé -Évolution de la fertilité minérale d'un sol acide sur une période de 10 ans dans les Vosges (France). Impact sur la minéralisation de l'humus. Un sol très acide des Basses Vosges (Nord-Est de la France), sous un peuplement d'épicéa adulte, a été analysé en 1986, puis en 1996. La composition chimique des horizons minéraux n'a que peu varié, mais la somme du calcium et du magnésium échangeables des horizons minéraux et totaux des horizons OL, OF et OH a diminué significativement, surtout celle de Mg qui a baissé de 30 kg·ha -1 en dix ans, soit environ 1,7 % par an du magnésium échangeable présent en 1986. Cette diminution, préoccupante pour l'avenir, peut s'expliquer par un pic de minéralisation de l'humus pendant les étés chauds combiné avec l'incapacité des horizons minéraux, fortement saturés en aluminium, à retenir le calcium et le magnésium provenant de la minéralisation des couches d'humus. Ces éléments sont donc perdus par drainage au lieu d'être prélevés par les racines. Dans ce sol, pauvre en minéraux altérables, cette perte ne peut pas être compensée par l'altération. Une telle situation se produit certainement aussi en fin de révolution, lorsque les horizons humifères sont exposés à la lumière et à la chaleur. Ainsi, la dégradation de l'humus de mull en dysmoder et, plus tard, sa minéralisation, couplée avec une forte teneur des horizons minéraux en aluminium échangeable, conduit à de fortes...

Effect of tree species substitution on organic matter biodegradability and mineral nutrient availability in a temperate topsoil

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Tree nutrition of Norway spruce as modified by liming and experimental acidification at the Höglwald site, Germany, from 1982 to 2004

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Effects of the clear-cutting of a Douglas-fir plantation (Pseudotsuga menziesii F.) on the chemical composition of soil solutions and on the leaching of DOC and ions in drainage waters

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