Short-term impact of de-vegetation on organic/inorganic interactions and cation transfers in uppermost soil horizons

Abstract

The soil solutions of a natural soil covered by grass and of the same soil after grass removal were collected and analyzed after each rainfall and percolation through the two soils during a fifteen-month experiment. To identify and quantify the water–mineral–plant interactions during this period of time, plastic tubes containing calcite and smectite particles were inserted into the two soils, some powder of both being recovered after three and fifteen months, water leached and the leachates analyzed. The contents of various elements including the rare-earth elements were measured in the soil solutions and the water leachates, to identify the extent of the interactions and evaluate the contribution of the plants. The immediate impact of de-vegetation was recorded in the soil solutions that exported systematically more Si and Ca, and often more Mg from de-vegetated soil. The supplement of exported Si was probably released by altering microorganisms as a response to de-vegetation, whereas that of Mg resulted probably from dissolution of oxy-hydroxides and that of Ca from partial dissolution of the calcite reference mineral. The removed elements were about 50 times higher in the soil solutions than in the plain rainwater before percolation through the soils. The contents of the dissolved organic carbon and ammonia of the soil solutions from de-vegetated soil were about one third higher than in those of the vegetated soil.On the basis of the elemental contents of the soil solutions that percolated through the two soils, removal of plants did not significantly affect adsorption of the nutrient K on the inserted smectite and calcite during the initial three months. However, less K was adsorbed on smectite and calcite of the de-vegetated soil than on the same minerals of the same soil covered with grass during the following twelve months, indicating in turn that more K was removed from de-vegetated soil within a one-year time.