Cycle biogéochimique du potassium sur le site expérimental de Skogaby : une approche par mesures du rapport K/Rb

Abstract : The ministerial conferences of Rio (1992) and Helsinki (1993) resulted in the concept of sustainable forest management. Because forests soils are often acidic and low in base cations, and because export of biomass materials may deplete soil nutrients, the ability of the vegetation to increase the chemical weathering in soils must be taken into account to predict the long-term sustainability of ecosystem functioning. This work is a contribution to the project Quantifying Weathering for Sustainable Forest Management (QWARTS). Specifically, the cycling of K, on the Skogaby experimental forest site, was investigated by using K/Rb ratios of clay minerals and biomass. An approach by total geochemistry and extractions of samples of soils, humus, litters, needles, stemwood and bark with HCl, NaTPB (Na tetraphenyl borate) and HNO3 + HClO4 was used. The HCl extractions of the soil showed a vertical K/Rb gradient in the profiles, indicating an influence by biogeochemical cycling in the soil to a depth of 70 cm. A contrasting behavior of K and Rb in the soil was highlighted by an accumulation of Rb (2 to 7 kg/ha) between 20 and 70 cm of depth. The amount of reactive K, held by clay minerals, and previously circulated through the biomass in a longterm, was estimated at between 700 and 2100 kg/ha. Furthermore, higher K and Rb concentrations were found in biomass samples from an ammonium sulphate treatment (100 kg of N and 114 kg of S per ha annually, showing that this treatment increased the biogeochemical cycling of K compared to the control. Finally, HCl and NaTPB extractions showed similar variations of the K/Rb ratio with depth and, therefore, both seem adapted to the study of non-exchangeable K in soil clay minerals.
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Master thesis
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Mélanie Court. Cycle biogéochimique du potassium sur le site expérimental de Skogaby : une approche par mesures du rapport K/Rb. Sciences de la Terre. 2014. ⟨hal-01841107⟩

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