Dynamic role of “illite-like” clay minerals in temperate soils: facts and hypotheses |
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Authors: | P Barré B Velde L Abbadie |
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Institution: | (1) Laboratoire Biogéochimie et Ecologie des milieux continentaux, UMR 7618, Université Pierre et Marie Curie-Paris 6, ENS, CNRS, 46 rue d’Ulm, 75230 Paris cedex 05, France;(2) Laboratoire de Géologie, UMR 8538, ENS, CNRS, 24 rue Lhomond, 75231 Paris cedex 05, France |
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Abstract: | Analysis of new data and reinterpretation of published information for clay minerals found in temperate climate soil profiles
indicates that there is often a gradient of “illite-like” clay minerals with depth. We used the term “illite-like” because
these observations are based on X-Ray Diffractogram patterns and not on layer charge measurements which allow to define properly
illite. It appears that “illite-like” layers are concentrated in the upper, organic - rich portion of the soil profile both
under grassland and forest vegetation. “Illite-like” layer quantity seems directly related to soil potassium status. Indeed,
intensive agriculture practises without potassium fertilization reduce “illite-like” content in surface soils, whereas several
years of potassic fertilization without plant growth can increase “illite-like” content. The potassic soil clay mineral, illite,
is particularly important in that it can be the major source of readily available potassium for plants. Spatial and temporal
dynamics of clay minerals should be related to the potassium cycle. We propose that the frequently observed general trend
of increasing exchangeable potassium in the top soil can be correlated with an increase in “illite-like” in the clays and
that the decrease of potassium caused by intensive agricultural practices leads to “illite-like” layer destabilization. This
vision of “illite-like” layer as a potassium reservoir refueled by plants and emptied by intensive cropping renews the concept
of potassium availability and indicates a need to be discussed as well in natural ecosystems as in cultivated ecosystems. |
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Keywords: | Clay minerals Illite Potassium availability Potassium cycle Plant– soil interactions Soil |
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