Six irrigation treatments consisting of replenishing the water extracted from the 0-60 cm or 0-120 cm layer, were applied to a 10-year-old apple orchard. The highest yield and fruit size were obtained by irrigating to 60 cm depth when soil moisture to this depth dropped to 40% available water during the 2 months of intensive fruit growth. During the rest of the season this treatment was irrigated to 60 cm whenever the 0-60 cm layer dropped to wilting point and to 120 cm whenever the 60-120 cm layer dropped to 60% available water. The relative water extraction from the 60-90 cm layer was the highest in this treatment. Increasing water uptake from layers below 120 cm by watering them was not effective. Climatic conditions favoring high rates of evaporation increased the relative contribution of layers deeper than 90 cm in all plots. The proportion of water loss from the 0-30 cm layer increased with the number of irrigations.
Fruit growth rates and yields of apple (Malus domestica Borkh.) collected from irrigation experiments from 1967–1980 in the Hula Valley of Israel indicated that the seasonal course of growth rate expressed in volume units was linear in optimal irrigation regimes regardless of the method of irrigation. Equations for converting the circumference measurements to volume units were developed for 5 commercial apple cultivars. Typical fruit volume growth lines are presented for growers use to control irrigation regimes in conjunction with the common pan evaporation coefficients.