What physical property drives capillarity in soils?

The physical property that drives capillarity in soils is primarily the attraction of water to soil particles. When water infiltrates the soil, it encounters various soil particles, including sand, silt, and clay. The water molecules are attracted to these particles due to adhesive forces, which enable water to move upwards against the force of gravity. This upward movement is what we refer to as capillarity.

While soil texture is significant in determining the size of the pores within the soil and, therefore, the extent and efficiency of capillary action, it is the attraction between water and soil particles that fundamentally facilitates capillarity. Larger soil particles, such as sand, may allow water to drain quickly, whereas smaller particles, such as clay, can hold water in small capillary spaces due to their higher surface area and the greater water retention capacity induced by the attractive forces.

Soil temperature and moisture levels can influence the rate of capillary action and the ability of soil to retain water, but they do not directly drive the capillary process itself. Hence, the direct and primary factor is the attraction of water to soil particles that governs capillarity in the soil.