Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology

TLDR

Crusting and erosion of cultivated soils result from aggregate breakdown and detachment of soil fragments by rain, and susceptibility is inferred from aggregate stability measurements; their relative importance depends on rain nature and soil physical/chemical properties. The authors review aggregate breakdown theories, analyze their links to crusting and erosion, and propose a unified framework for measuring aggregate stability to compare soils or climatic conditions rather than temporal changes. The study defines four mechanisms of aggregate breakdown—slaking, differential swelling, raindrop impact, and physico‑chemical dispersion—and uses a method combining fast wetting, slow wetting, and stirring after pre‑wetting to measure fragment size distributions.

Abstract

Summary Crusting and erosion of cultivated soils result from aggregate breakdown and the detachment of soil fragments by rain, and the susceptibility of soil to these processes is often inferred from measurements of aggregate stability. Here, theories of aggregate breakdown are reviewed and four main mechanisms (i.e. slaking, breakdown by differential swelling, mechanical breakdown by raindrop impact and physico–chemical dispersion) are defined. Their relative importance depends on the nature of the rain, as well as on the soil's physical and chemical properties. The relations between aggregate breakdown, crusting and water erosion are analysed, and existing methods for the assessment of aggregate stability are reviewed. A unified framework for the measurement of aggregate stability is proposed to assess a soil's susceptibility to crusting and erosion. It combines three treatments having various wetting conditions and energies (fast wetting, slow wetting, and stirring after pre‐wetting) and measures the resulting fragment size distribution after each treatment. It is designed to compare different soils, or different climatic conditions for a given soil, not to compare time‐dependent changes in that soil.