Orchard Mineral Nutrition: Ground- 

 appiied vs. Foiiar-applied Fertilizers 



James R. Schupp 



Highmoor Farm, University of Maine 



Why do apple growers spend time and money 

 spraying fertilizers on foliage when for centuries we 

 have been told that plants take up nutrients from the 

 soil via their roots? They do it in an attempt to 

 improve fruit quality and enhance its storage life. 

 Apple is somewhat unique among fruit crops in that 

 it is able to utilize a range of mineral nutrients 

 through its leaves. 



Many new products are available to apple grow- 

 ers for foliar feeding. Sometimes promotional mate- 

 rials suggest that rather dramatic results can be 

 obtained from using these products. One grower 

 recently calculated the expected results for his or- 

 chard based on such claims and found that if he 

 would simply use several of these products, his 

 yields would be 3000 bushels per acre with excellent 

 fruit size and virtually 100% packout. This yield is 

 three times that obtained in the best New England 

 orchards and a level of production at which fruit size 

 and quality would be very poor. Such an outcome is 

 impossible of course, and most manufacturers of 

 foliar nutrient products are careful to base their 

 product claims within the realm of possibility. Still, 

 many apple growers are uncertain what role foliar 

 sprays should have in their nutrition plan. 



The first step to any orchard nutrition plan is soil 

 and leaf analysis. Before applying any fertilizer in 

 any manner it makes proper sense to determine 

 whether or not there is need for nutrient supple- 

 ments, which ones are needed, and in what amounts. 

 This information provides the first answers to the 

 ground-applied versus foliar-applied question. 



Macronutrients 



If leaf and soil analyses indicate the need for 

 nitrogen, phosphorous, potassium, calcium, or mag- 

 nesium, the cheapest and most efficient way to apply 

 them is by ground application. Soil- applied fertiliz- 

 ers can be applied early in the spring before the busy 

 growing season and with little or no risk of damage 

 to the fruit or foliage. Soil-applied nutrients also 

 follow the natural pathway in the tree to all the 

 locations where growth and development are taking 



place. By contrast, foliar-applied nutrients are less 

 mobile and stay where they are absorbed. 



Micronutrienta 



Boron, manganese, copper, or zinc can be ap- 

 plied to either soil or foliage; however, foliar applica- 

 tions are more common, because it is easier to spray 

 the small amounts needed than it is to apply them to 

 the soU. Foliar applications allow "direct hits" to the 

 fruit and foliage where supplemental nutrition is 

 needed, and they allow for precision timing. The 

 grower can apply the nutrient at a critical time in the 

 growth stage when it is needed. Foliar fertilizers can 

 harm the fruit and foliage that they contact, so 

 usually, only small amounts are applied this way. 

 Growers should pay particular attention to recom- 

 mended rates and timings to avoid damage. Refer to 

 the label of the product and the New England Apple 

 Pest Management Guide for additional information 

 on rates, timing, and nutrient compatibility in the 

 spray tank. High-grade fertilizers, free from impu- 

 rities, are needed for foliar application, adding to 

 their cost. 



Special Nutrition Problems 



If a given nutrient is acutely deficient or if there 

 is a special nutritional problem that is harmful to 

 productivity or fruit quality, a combination of both 

 soil- and foliar-applied nutrients may be justified. 

 Table 1 lists several of the more common examples 

 where supplemental foliar nutrients are used to 

 correct specific problems. 



Perhaps the most common special nutritional 

 problem in apple is low fruit calcium. Developing 

 fruits compete with vegetative growth for calcium 

 during the first five to six weeks following bloom. 

 After this time, calcium uptake by the fruit via the 

 tree's vascular system essentially stops. 



If soil calcium levels are low, or if vegetative 

 growth is excessive, the fruit may be deficient in 

 calcium, leading to the appears rce of cork spot or 

 bitter pit and rapid loss of fruit q ality in storage. In 



20 



Fruit Notes, Spring, 1993 



