The Response of Laxton’s Superb Apple Trees to Different Soil Moisture Conditions

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Abstract
Eight-year-old trees of Laxton’s Superb apple on M.II rootstock growing on loamy fine sand of low moisture retention were used to study growth and crop responses to different soil moisture conditions from 1953 to i960 inclusive. Water was applied when soil moisture tensiometers set at 1 ft. depth indicated tensions of : A, 10 cm. Hg ; B, 20 cm. Hg ; C, 50 cm. Hg. Treatment D was unwatered. Water was applied to an area 12 ft. in diameter around each tree, which was about one-third of the ground area available to each tree. The average amount of water required by each treatment during a season was equivalent to : A, 4-1 ; B, 3-5 ; C, 2-1 inches over its whole area. Comparison of soil moisture deficits in the unwatered plots in the very dry season of 1959 with amounts of water applied to the other trees suggested that the rate of water loss throughout the experiment was not seriously affected by the treatments applied. The water treatments stimulated trunk and shoot growth ; growth differences between differently treated trees could be adequately explained in terms of soil moisture tension and root-occupied soil volume. Evidence was found of serious leaching under the wettest treatment, and this may have caused a lower growth and crop response to treatment A than to B in the later years of the trial. Crop increases were directly related to growth increases. Despite the marked effects of water treatments on shoot numbers and on crop increase the growth and crop relationship was virtually unchanged. Treatments A, B and C increased total crops by 40%, 46% and 25% respectively, and marketable crops by 44%, 55% and 42% respectively. There was no marked effect of treatment on fruit size, though the increased proportion of fruit of a commercial size from the watered trees was of importance. Treatment B provided the largest total and marketable crops, but treatment C provided the greatest increase in marketable crop for each inch of water applied.

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