IntroductionWe have studied soil as a physical system with particular attention to the movement of soil water and the diffusion and dispersion of chemical substances. To understand the fundamentals of water flow and contaminant transport, we developed and used analytical and numerical models of flow and transport in unsaturated soils. An example of water flow that we have not explicitly examined is the case of evaporation of water from the soil. Evaporation is an important component of the surface energy balance. The availability of energy and water are the main principles that dominate the evaporation process. Evaporation affects the water content of the soil available to plants and causes salinization of irrigated land. If evaporation is not controlled, a considerable amount of water can be lost from irrigated and rain-fed croplands. Evaporation of soil moisture not only leads to water loss, but also risks salinization of the soil. This danger is greatest in arid areas, where annual precipitation is low, irrigation water is brackish, and the water table is high. The rate and amount of evaporation are affected by many soil characteristics, tillage, and environmental interactions. In the absence of vegetation and when the ground surface is subject to the effects of radiation and wind, evaporation occurs entirely from the ground. Under large annual crops, the soil surface may remain largely bare during periods of plowing, planting, germination, and early seedling growth, periods during which evaporation may deplete moisture from the soil surface. soil and thus hinder the growth of young plants during their greatest period. vulnerable stage. The problem can also be acute in young orchards, where the soil surface is often kept permanently bare for several years, as well as in arid areas far...... middle of paper ...... decrease of soil conductivity. This results in a decrease in the rate of evaporation with respect to time. How long the initial drying phase can last depends on the evaporativity. Low evaporativity will increase the duration of the first drying stage. The relationship between hydraulic conductivity K and water content can be seen below: Other topics - Flow processes can be isothermal or non-isothermal - They can be interactions between liquid flow and water gradient temperature, heat conduction and vapor in the soil area. - Crack inside the soil matrix forming secondary evaporation planes. Depends on the physical and conductance properties of the soil: - water content of the soil body - soil water potential - soil conductivity - texture - compaction - depth of soil stratification to the water table. Depends on regular (diurnal, seasonal) or irregular frequency