Articles
EFFECTS OF NITROGEN SUPPLY ON SOME COMPONENTS OF APPLE FRUIT QUALITY
Comparisons were made in two separate trials.
In the first, nitrogen fertilizers were applied annually at 50, 100, 200 and 300 kg N ha-1 while in the second, a single application of 200, later 100 kg N ha-1 was made in November, March, April or July.
Nitrogen was applied as a mixture containing two thirds of calcium nitrate and one third of ammonium nitrate.
Fruit size of Gravenstein apples increased considerably with increasing rates of nitrogen, whereas Golden Delicious and Cox’s Orange Pippin showed less effect.
There was a slight increase in yield with applied nitrogen but this was modified by the routine thinning treatments designed to improve fruit quality.
Yields averaged about 40, 30 and 20 t ha-1 for Golden Delicious, Gravenstein and Cox respectively.
There was an indication that a July nitrogen application gives somewhat smaller fruits than the other application dates.
Cell size in all cultivars used was not influenced either by the rate nor the date of nitrogen application.
Russetting of the fruits was unaffected by either the rate or time of nitrogen application.
Fruit ground colour was greener and red colour poorer in high nitrogen than in low nitrogen fruit.
The concentration of titratable acid sometimes was highest in fruit from low nitrogen plots.
Moreover, decomposition of the acids seemed to progress more slowly in low nitrogen than in high nitrogen fruit.
Soluble solids were not affected by nitrogen supply.
There is a close negative relationship between colour and flavour.
Thus the higher rates of nitrogen were reflected in the poorer flavour of the fruits.
The incidence of bitter pit was increased significantly by the higher rates of nitrogen in Gravenstein but not Cox.
The data suggest that fruits from trees receiving nitrogen in July are less susceptible to bitter pit than those from trees receiving the fertilizer at the other times investigated.
Though susceptibility of the fruit to bitter pit was negatively related to the calcium concentrations when fruits from single trees were analysed, the different nitrogen levels showed no influence on mean fruit calcium content of Cox’s Orange Pippin, Golden Delicious and Gravenstein.
As for the nitrogen application rate, there was some evidence that a July application might increase fruit calcium between August and picking and, in the following year, during the very early stages of fruit development.