Nitrogen and Water Effects on the Nutrition, Growth, Crop Yield and Fruit Quality of Orchard-Grown Cox’s Orange Pippin Apple Trees

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Abstract
Nitrogen was applied at 26, 78, 130 or 182 kg N ha-1 as a single annual dressing either in October or March to Cox’s Orange Pippin apple trees on MM. 104 rootstock that were irrigated early (June only), late (July to mid-September), early + late, or left unirrigated. Treatments continued for nine years. The lowest rate of N did not maintain a non-limiting N status in the trees indicated by a leaf level of 2.4% of dry matter. All the higher rates did so, and, compared with minimum N, increased growth, initial set and fruit numbers at harvest but decreased fruit size. Irrigation increased growth and cropping, but its effect on growth was greatest when rainfall was well below average (June-August) and when cropping of mature trees was heavy. Early irrigation increased fruit numbers at harvest and decreased fruit size compared with no irrigation. Late irrigation had no effect on fruit number but had a very marked effect on size and quality, increasing the two highest quality grades by 67% over unirrigated trees during 1971–5 when 80% of the cumulative crop yield was produced. Maximum crops of high quality were obtained by the combination of adequate N (78 kg N ha-1) to ensure fruit set, and late irrigation to ensure good size and quality. Early + late irrigation was less effective. Increasing N reduced the incidence of bitter pit, but irrigation reduced it only in fruit from trees that had received the lower N rates. There were no growth or cropping effects due to the time of N application.