WATER-USE, WETTED SOIL VOLUME, ROOT DISTRIBUTION AND YIELD OF AVOCADOUNDER DRIP IRRIGATION

The effect of three water use (WU) levels corresponding to 0.3, 0.6 an d 0.9 Ep (Ep=Evaporation ''A'' pan) on wetted soil volume, root distri bution and yield of avocado cv. Fuerte was investigated over a 5-year period at Chania, Greece. The average amounts of irrigation water appl ied annually (in addition to rain) for the three WU levels were 238, 5 53 and 868 mm, respectively. Soil volumes, with a volumetric soil wate r content percentage (theta) corresponding to a soil water potential ( psi(s)) higher than -0.1 MPa, increased markedly from 0.3 to 0.6 Ep, a nd slightly from 0.6 to 0.9 Ep WU levels, being 26.3, 41.7 and 52%, re spectively. Deep percolation did not occur at 0.3 Ep, was moderate but acceptable at 0.6 Ep, and high at 0.9 Ep. Root distribution was simil ar in all treatments. Some 72% of the root system was concentrated in the upper 0.5 m soil layer and within 2 m on either side of the drip l ine. Root density (RD) increased greatly from 0.3 to 0.6 Ep, and sligh tly from 0.6 to 0.9 Ep level. RD in relation to theta did not show any notable difference between WU levels. Root growth rate, estimated by the lateral to main root ratio (r), was higher in a 0 range of 20 to 3 0%, corresponding to a psi(s) range of -0.05 to -0.3 MPa for the soil in the experiment. Yield at 0.3 Ep was lower than at 0.6 and 0.9 Ep WU levels among which no significant differences were seen. Size of indi vidual fruits and oil content were not significantly different between treatments. When water saving, deep percolation, wetted soil volume, root development, and yield quantity and quality are taken into accoun t, then a WU level of 0.6 Ep can be considered optimal under the condi tions of this experiment.