GROWTH AND WATER-USE OF EUCALYPTUS-GRANDIS AND PINUS-RADIATA PLANTATIONS IRRIGATED WITH EFFLUENT

We studied the growth and water balance of young plantations of Pinus radiata D. Don and Eucalyptus grandis W. Hill ex Maiden. irrigated wit h effluent for 3 years in a climate of high net evaporation. The plant ations were irrigated weekly with secondary-treated municipal effluent at the estimated water-use rate, or at nominally twice or half this r ate. Control plots were irrigated with bore water at their estimated w ater-use rate. Both species grew rapidly when irrigated with either ef fluent or bore water. The eucalypts irrigated with effluent at the est imated water-use rate closed canopy in 24 months, and at 34 months, me an dominant height was 12.1 m, stand basal area was 12.2 m(2)ha(-1), v olume was 51.2 m(3) ha(-1), LAI was 5.7, and foliage mass was 6.5 Mg h a(-1). The pines in the corresponding effluent treatment had not close d canopy by 34 months. At this time, mean height was 5.0 m, stand basa l area was 9.6 m(2) ha(-1) volume was 29.7 m(3) ha(-1), LAI was 3.5, a nd foliage mass was 7.3 Mg ha(-1). Water use by eucalypts was consiste ntly higher than by pines, commensurate with their more rapid early gr owth, but the difference was not in proportion to the difference in le af area. In the third year (when the eucalypts had a closed canopy), t he eucalypts used 22% more water than the pines, but the annual mean L AI of the eucalypts was three times greater than that of the pines. Th e results suggest that (1) plantation water use by the two species on the same site will be similar for the same stage of canopy development , (2) eucalypts are not inherently more profligate consumers of water than pines when soil water is not limiting, and (3) stomatal control l imits growth and water use of E. grandis in arid environments.