Quality of fresh and dried fruit of apricot (cv. Moorpark) in response to soil-applied nitrogen

Abstract

The effects of soil applications of nitrogen on the quality of fresh and dried fruit from 12-year-old apricot Prunus armeniaca cultivar Moorpark trees growing on an orthic Tenosol in the Riverland region of South Australia were studied over 3 years. The experiment was set up in a randomised complete block design with 6 annual rates of nitrogen (0, 250, 500, 750, 1000 and 1250 g/tree.year) applied in the form of ammonium nitrate. Application was split into 30% at budburst, 30% six weeks after budburst and 40% after harvest. Firmness of fruit was significantly reduced as the rate of applied nitrogen increased. The flesh of individual fruits ripened more evenly when 0 or 250 g nitrogen/tree.year was applied, compared with rates in the range 500–1250 g nitrogen/tree.year. Application of nitrogen significantly increased the pH of fruit. The total soluble solids level of fruit from trees that received 0 or 250 g nitrogen/tree.year, was significantly lower than from trees that received 750 or 1250, but not 1000 g nitrogen/tree.year. Application of nitrogen did not significantly affect the concentration of sulfur dioxide in fresh fruit measured after sulfuring, but the concentration of sulfur dioxide in fruit at the completion of drying was significantly increased. The application of nitrogen did not affect the drying ratio of fruit. Nitrogen application increased the rate of darkening of dried apricots in storage in each of the three years. Relationships were found between time taken for dried apricots to darken to an unacceptable level and nitrogen concentration in harvested fruit. It is suggested that to assist in the management of darkening of dried apricots in storage, annual nitrogen application rates on an orthic Tenosol need to be below 500 g/tree.year and ideally below 250 g/tree.year.