Organic Matter Influence on Clay Wettability and Soil Aggregate Stability

Soil organic matter is thought to increase aggregate stability by lowering the wettability and increasing the cohesion of aggregates. In southwest France, thick humic loamy soils (Vermic Haplubrepts) have been intensively cropped for 40 yr, decreasing the soil organic pool and lowering the soil agregate stability. This study assessed (i) the contribution of organic matter to aggregate stability by decreasing aggregate wettability and (ii) the specific role of clay‐associated organic matter. Soil samples with a C content of 4 to 53 g kg−1 were sampled and soil aggregate stability was measured. Aggregate wettability was assessed by measuring water drop penetration times on individual 3‐ to 5‐mm aggregates. The