Effects of Time of Application of Inorganic Nitrogen Fertilizers on Apple Trees in a Grassed Orchard

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Abstract
Sulphate of ammonia, calcium nitrate or Nitrochalk was applied as a single annual dressing in October, December, February, April, June or August to Cox’s Orange Pippin apple trees on M.2 rootstock over a 14-year period, whilst control trees received no supplementary nitrogen. The treatments affected the soil physical and chemical conditions, sward composition, and leaf and fruit mineral composition but, despite these effects, there were no long-term differences in tree growth or cropping between the kinds of fertilizer used or their times of application. Nitrogen effects were progressive ; in the first four years there was a time X kind interaction on cropping; in the next five years only the time of application affected cropping and in the final five years neither time nor kind had differential effects on cropping, although N increased yield compared with the control. Growth was also increased by the N treatments but, again, only in the latter years of the experiment. Leaf N was highly correlated with rainfall during March to August. In all but the first two and the last of the 14 years, rainfall was above the long-term average for the site. February appeared to be the best month in which to apply sulphate of ammonia and calcium nitrate, and December for Nitrochalk application.

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