Do climate and land use affect the pool of total silicon concentration? A digital soil mapping approach of French topsoils

Silicon (Si) is the second most abundant element in the Earth's crust after O. Its concentration in soils is highly variable from < 1% to greater than 45%. Parent material is well known to be a major parameter for explaining this variability. In this study, we proposed to analyze the impact of climate and land use on the total Si concentration in soils and to explore the link between total Si and plant available Si (PAS). To do so, we based our analysis on the French soil monitoring network considering the upper soil horizon that was thought to be the most impacted by both the effect of land use and climate and was also the most important horizon in terms of plant availability. In order to extract the impact of climate and land use and for digital mapping purposes, we stratified the database by parent material and soil-types. This stratification was based on the classification used in the 1:100,000 French soil map and 1:100,000 French soil parent material map. For non carbonated soils, we showed that Si concentrations was decreasing with annual rainfall, evidencing a climatic effect on the total Si concentration of French topsoils. No significant effect of the land used could be identified. At last, we showed that PAS (by the CaCl2 method) is negatively weakly correlated to total Si concentration. This relationship is however variable among soil classes.