Growth and quality of apples as affected by different irrigation treatments

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Abstract
Summary Granny Smith apple trees were irrigated at four levels of total available soil water (TAW) * * Soil water available between field capacity and permanent wilting in the 0–700 mm or 0–1100 mm layer, depending on the rooting depth. in the soil, viz. 85%, 65%, 45% and 25%. The treatments were applied during each of four phenological phases of the trees for four years. Soil water potentials at the time of irrigation were – 19 kPa and – 1189 kPa, respectively, for the 85% and 25% TAW levels. Total irrigation amounts varied between 570 mm and 850 mm, the recommended amount being 600 mm of water. A significant linear increase in fruit circumference growth with an increase in TAW level was observed for phenological phases 2 and 3. The main part of total growth was completed during phase 2. The tendency for fruit growth to decrease over years was probably due to increased yield loads. Most shoot extension growth was completed during phase 1. More vigorous shoot growth took place during phase 2 for an 85% TAW level as compared to a 25% TAW level. Trunk growth was completed mainly at the end of phase 2 for the higher TAW levels (85% and 65%), but for the lower TAW levels (45% and 25%) already by the end of phase 1. This property was, therefore, positively correlated with an increase in water application during phases 1 and 2, and even, if only slightly, during phase 3. Apple size distribution was markedly affected by the different TAW levels with much emphasis on the negative influence of soil water stress. A decrease in TAW levels during the main fruit development period (phases 2 and 3) resulted in a decreased fruit size. Although the treatment effects were not so obvious during phase 2, an 85% TAW level should be favoured by growers during both phases. A physiological disorder such as watercore was found to worsen with an increase in TAW level. On the other hand, a strong increase in sunburn with a decrease in TAW level was observed. Categorized superficial scald was not independent of the treatments but the results are difficult to interpret. Trends in scald incidence indicate a positive correlation with the TAW levels during phases 3 and 4. An increase in the occurrence of bitter pit was found during all phases when the TAW level was raised.

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