Evapotranspiration from wheat and pasture in relation to available moisture.

Abstract

The changes of soil moisture to a depth of 5 f t in a simple crop rotation and under permanent pasture during 1948-1949-1950 have been followed in detail. Calculations have been made on a monthly basis of the water storage in the soil and of the evapotranspiration from wheat and pasture and of losses from a bare fallow. It is shown that in these experiments the relationship between evapotranspiration, evaporation from water, storage of water in the soil, and rainfall can be expressed in the form dItr /dW = ~ ( 2.4 – Itr), where Itr = Etr/Ew0.75= 2.4 when available water is no longer limiting, and c = 0.12 for wheat, c = 0.10 for pasture, Etr = evapotranspiration, Ew =evaporation from a free water surface, W = stored water plus rainfall = available water. Water losses from a bare fallow were found to be determined principally by rainfall and soil storage.