INFLUENCE OF SOURCES, RATES AND TIMES OF SOIL APPLICATION OF NITROGEN ON APPLE TREE PERFORMANCE AND FRUIT QUALITY IN ONTARIO, CANADA

It is well known that excessive nitrogen generally results in poor quality fruit at harvest that does not store well.
McIntosh, a variety widely grown in Ontario, is particularly sensitive.

The effects of time of application, rate and source of nitrogen fertilizer on fruit quality were studied in trials on a coarse sandy loam soil with low moisture and nutrient holding capacities.
Nitrogen fertilizers were applied on April 1, 15 or 30. The effects were compared of two sources of nitrogen, ammonium nitrate with potassium chloride and potassium nitrate, on mature McIntosh trees.
The same amounts of nitrogen and potassium were provided by the two sources and the fertilizers were applied to a 0.5 m diameter circle of soil around the base of the tree.
In a similar experiment with Northern Spy, the fruit of which is subject to bitter pit, calcium nitrate was compared to ammonium nitrate.

With both varieties, fruit colour and keeping quality were more closely related to time and rate of application of nitrogen than to source.
The higher rate of nitrogen applied on April 30 resulted in fruit that was of poorer colour and storage quality.
Late application or high rates of nitrogen may also leave trees more sensitive to freezing injury.

Bitter pit was not a serious problem throughout the experiment and soil calcium nitrate applications did not result in a lower incidence of bitter pit in the crop than ammonium nitrate except in 1978 when bitter pit was generally more prevalent.

Seasonal changes in leaf nitrogen were more closely related to time and rate of application than to source.
Late application resulted in higher leaf nitrogen late in the season.
Rainfall also affected seasonal leaf nitrogen patterns.

Symposium on Mineral Nutrition and Fruit Quality of Temperate Zone Fruit Trees

R.A. CLINE

https://doi.org/10.17660/ActaHortic.1980.92.38