The effects of evaporation, potential transpiration, and rainfall on the depletion of soil moisture by irrigated perennial pasture

Abstract

Depletion of soil moisture by an irrigated perennial pasture is shown to be closely related to an evaporative index (E-R), the accumulated difference between evaporation ( E inches) and rainfall (R inches) subsequent to the last irrigation. This index, calculated for three types of evaporimeter, is shown to be directly proportional to (Et-R) the difference between Penman's potential transpiration (Et) and rainfall, for drying cycles of more than seven days duration. It is suggested that (E-K) might be a useful guide for irrigation scheduling, wherever Penman's estimate of potential transpiration is found to be reasonably accurate.