Deriving empirical models of evaporation from soil beneath crops in a Mediterranean climate using microlysimetry

Microlysimeters were used to measure evaporation from bare soil and from so il under wheat and lupin canopies. The data were used to develop empirical relationships between evaporation, potential evaporation, soil water conten t, and leaf area index to allow estimation of evaporation losses in seasons when evaporation was not measured directly. Canopy cover was found to decr ease evaporation losses from soil in both Stage 1 and 2 evaporation. This f inding has significance to applications of the Ritchie model (1972) in Medi terranean climates since the model assumes Stage 2 evaporation to be indepe ndent of canopy cover. The empirical models derived during one season were successful in predicting evaporation from soil beneath crops during a secon d season. The model parameters were derived over the complete range in wate r content, leaf area index, and potential evaporation expected for crops at the site, suggesting that the models may be reliably applied to predict ev aporation from soil at the site for other seasons. The technique may be use ful for general application in estimating evaporation from soil beneath cro ps in field studies, although the model parameters may be site and/or soil specific. Further research into the generality of the relationships is warr anted.