COMPONENTS OF THE WATER-BALANCE FOR TREE SPECIES UNDER EVALUATION FOR AGROFORESTRY TO CONTROL SALINITY IN THE WHEAT-BELT OF WESTERN-AUSTRALIA

The soil water balance technique was used to study evaporation from two fodder tree species, ten Eucalyptus species and annual pasture over a three year period after planting in the Western Australian wheatbelt. Evaporation is the total water loss by the processes of transpiration, evaporation from the soil surface and evaporation of water intercepted by plant canopies. Evaporation from both fodder trees and from seven of the Eucalyptus species was greater than from pasture for one or more of the study years. The maximum difference in evaporation between trees and pasture was 82, 84 and 70 mm in the first, second and third study years, respectively. Higher evaporation from trees was associated with greater depletions in soil water than occurred beneath pasture. Upward movement of water from wet soil beneath the root zone was found under trees, with a maximum flux of 30 mm observed over a one year period beneath E. camaldulensis. The water use efficiency of fodder trees was significantly higher than for most Eucalyptus species, due to greater yields from fodder trees. Biomass production was found to be a good indicator of the water use of eucalypts over the first two years of growth, but the relationship between productivity and water use was found to differ for species with tree and mallee forms. In the third year of study, obvious differences in the relation between water use and yield were observed for some species of eucalypts with high evaporation.