Water in unsaturated soil

Abstract

Water in soil usually fills soil pores only partially, therefore soil unsaturated with water is the prevailing state of soil. The soil unsaturated with water is a necessary condition for the majority of the plants that grow in the environmental conditions of Europe. The diagnosis and prognosis of the soil-water regimen is necessary to manage the soil-water content to reach maximum yields. This chapter defines the basic hydrophysical characteristics of an unsaturated zone of soil; the relationship between soil-water matric potential and volumetric soil-water content (so-called retention curve) and soil hydraulic conductivity as a function of soil-water matric potential and methods of their estimation are described. The Darcy–Buckingham equation is presented, as well as the equation of Richards that describes transport of liquid water in unsaturated soil. The transport of water vapour in the unsaturated soil is quantified by soil-water diffusivity, as well as by the coefficient of water-vapour diffusion of the soil, which is quantitatively described too.