Soil aggregation may be a relevant indicator of nutrient cation availability

Abstract

Key message: Aggregation was studied in two acidic forest soils (NE France) to investigate the potential link between available Ca and Mg content and soil aggregate size distribution and properties. Clay content influenced the aggregation status while clay mineralogy influenced aggregate stability and dynamics. Aggregation status and reactivity of soil components contributed to the difference of exchangeable Ca and Mg content in topsoil between the two sites. Context: Though nutrient fluxes are important to define forest soil chemical fertility, the quantification of nutrient reservoirs in the soils and their availability to tree uptake is essential. A thorough understanding of nutrient availability requires an investigation of nutrient location and distribution in the soil solid phase. Aims: The general aim was to investigate the potential link between available Ca and Mg content and soil aggregate size distribution and their properties (chemical, physical, mineralogical). Methods: Soil aggregates were separated according to three size classes (200–2000 μm; 50–200 μm; < 50 μm) in two forest soils of the Lorraine plateau (France), both classified as Luvisols ruptic. The physical, chemical, and mineralogical properties were measured for each aggregate class. Results: We showed that the relative abundance of an intermediate aggregate class [200–50 μm] was relevant to explain the difference of exchangeable Ca and Mg between sites. These aggregates were the poorest in organic and reactive mineral components and were unstable, which may mitigate the retention of Ca and Mg by ion-exchange. Conclusion: This study highlights the role of aggregation and reactivity of soil components as relevant determinants of cation availability to tree uptake in soils.