3 Irrigation Systems pdf

Water balance method using pan evaporation

The water use of a crop (evapo-transpiration) can be estimated from

measurements of these weather conditions.  The most common method uses

evaporation from an evaporimeter (the weather Bureau has pans at about 12

stations in Tasmania with US Class A pans), and applies a Crop Factor that

relates estimated crop evapo-transpiration to pan evaporation.

Daily water use is accumulated until the “Refill Point” is reached, and then

irrigation is applied.

Example calculation; assumes the soil is at field capacity 31 December