Capillarity

Capillarity emerges from interactions between air-water interfaces and soil surface and pore spaces. The tendency of water to adhere and spread over wettable surfaces while minimizing air-water interfacial area gives rise to spontaneous capillary rise in soil pores and crevices and to water retention against forces of gravity. Capillarity affects soil aqueous phase configurations that determine hydraulic pathways for water flow in unsaturated soil towards plant roots and surface evaporation, and sustain gas and nutrient diffusion pathways for biological activity. Capillary effects vary with soil type (surface and pore space properties) and contribute to the soil matric potential (along with film adsorption).