The irrigation depth is the amount of water that needs to be applied to an irrigated system when soil water is reduced to the specified depletion level. A definition for each data item that needs to be entered is provided below.
Soil water holding capacity is the amount of water that can be stored in the in the soil and extracted by the plant. It is generally defined as the amount of water needed to raise soil moisture content from the permanent wilting point to field capacity.
Depletion is the percentage of the soil's water holding capacity that will be used for ET.
Root depth is the distance measured from the surface of the soil to a depth that contains most of the plant's root system (80%-90%.) This should not be confused with the depth reached by the deepest root that can be found.
Irrigation efficiency is the percentage of water applied through the irrigation system that remains in the root volume after irrigation is completed. Irrigation efficiencies are less than 100% becuase of evaporation, wind drift, percolation and runoff losses. The irrigation efficiency of a well designed and operated sprinkler system is from 60% to 70%.
Calculated irrigation depth is the amount of water that needs to be applied to the irrigated system based on the parameters above. For convenience, the value is also presented in gallons for every 1000 square feet.
Developed by J. Xin and F.S. Zazueta, March, 2000.