EFFECTS OF MINERAL NUTRITION ON FRUIT QUALITY AND NUTRITIONAL DISORDERS IN APPLES

Several mineral nutrients can influence fruit quality and disorders of apple. Among these, nitrogen (N), potassium (K), phosphorous (P), calcium (Ca), and boron (B) are most often correlated to apple fruit quality and disorders. Leaf mineral analysis is a useful tool to diagnosis apple tree deficiencies but often is poorly related to fruit quality. Using fruit analysis alone or in combination with leaf analysis often permits more precise prediction of fruit quality. Over the last several years, we have developed several models for predicting apple fruit quality. In addition, we have examined the effects of various orchard factors and cultural practices, such as irrigation, rootstocks, and fertigation and foliar application of nutritional sprays, on apple fruit mineral composition and quality. A ranking of major minerals has been developed that predicts fruit quality within a year and between years. Increasing fruit N is inversely related to fruit yellow or red colour and positively associated with fruit respiration and ethylene. Fruit Ca tends to be imprecisely related to bitter pit and fruit firmness. Potassium fertigation in four apple cultivars increased fruit size, yield, acidity, and colour, but decreased firmness at harvest. Multiple sprays of soluble Ca often reduce bitter pit and usually but not always increase Ca concentrations in subdermal cortical tissue. Early-season Ca sprays often are more effective than later sprays at reducing bitter pit; however, later applications of Ca have a greater influence on fruit Ca concentration. The B concentration of apple fruit is much more strongly affected by early season B sprays that are B in leaves. Fruit from B-sprayed trees may exhibit quality loss due to B excess even though leaf B appears normal. Water stress reduced leaf and fruit K but increased leaf Mg. An overview of several orchard factors on mineral nutrition and fruit quality and disorders will be presented.