Water Balance in Root Zone of Soils: Theory, D.L. Nofziger General Description Model Description Simplifications Glossary Bibliography and Contributors Water Balance in the Root Zone

The movement and storage of water in surface soils is important for economic and environmental reasons. The ability of a soil to store water in the root zone determines its ability to support plant growth and crop production. Water moving through the root zone has the potential of carrying chemicals downward to the underlying aquifers. Rainfall and irrigation water entering the soil tends to replenish the soil storage reservoir and extend its ability to support plant life. If infiltrating water exceeds the storage capacity of the soil root zone, the excess water tends to move downward through the soil. This deep drainage contributes to recharging the aquifer below. The challenge to farm managers is to provide sufficient water for producing a crop while limiting the amount of water and dissolved chemicals moving deeply into the soil. This software uses the water balance concept to estimate water available for plants and water drainage below the root zone. The basic concept is just a statement of the principle of conservation of mass. It can be represented by the equation Infiltration- Evapotranspiration – Increase In Storage = Drainage where Infiltration represents the amount of water entering the soil surface from rainfall or irrigation, Evapotranspiration represents the amount of water leaving the soil by surfac