Perspectives on the misconception of levitating soil aggregates

Abstract

Abstract. Soil aggregation is an important process in nearly all soil and land-use types across the globe. Aggregates develop over time through a series of abiotic and biotic processes and interactions, including plant growth and decay, microbial activity, plant and microbial exudation, bioturbation, and physicochemical stabilization processes, and are greatly influenced by soil management practices. Together, and through feedbacks with organic matter and primary soil particles, these processes form dynamic soil aggregates and pore spaces, which together constitute a soil’s structure and contribute to overall soil functioning. Yet, the concept of soil aggregates is hotly debated, leading to confusion about their function or even existence. We argue here that the opposition to the concept of soil aggregation likely stems from the fact that the methods for characterization of soil aggregates have largely been developed in the context of arable soils, where tillage promotes the formation of discrete soil aggregates that are easily visible in the topsoil. We propose that the widespread use of conceptual figures showing detached and isolated aggregates can be misleading and has contributed to the skepticism towards the validity or relevance of studies on soil aggregates. However, the fact that we do not always see distinct aggregates within soils in-situ does not mean that aggregates do not exist. Here, we illustrate how aggregates can form and dissipate within the context of undisturbed, intact soils, highlighting the point that aggregates do not necessarily need to have a distinct physical boundary and can exist seamlessly embedded in the soil. We hope our contribution helps to alleviate the debate on soil aggregates and supports the foundation of a shared understanding on the characterization and function of the ‘dual nature’ of soil structure.