Formation of Vesicular Structure in Soil

Vesicular structure observed under irrigation furrows of several high‐silt soils is described. The structure is induced by the succession of wetting and drying cycles that accompany irrigation. The degree of drying before irrigation, the number of irrigations and the surface tension of water are important factors in the structure formation. The vesicular structure is probably caused by capillary pressure within the air‐filled voids surrounded by water. The soils involved are unstable when nearly saturated, and the capillary pressure is sufficient to form the trapped air into spheres. Swelling and shrinking accompany the wetting and drying, so that more air is trapped each cycle and the volume of vesicles increases with number of irrigations. The size of vesicles increases with number of irrigations as small vesicles merge to become larger ones, and thus decrease the surface area per unit volume.