and a smaller percentage of pear orchards, are excessively high in 

 N. The effects of high N on apples are perhaps being masked at 

 harvest by use of growth regulators, especially Alar, but growth 

 regulators cannot mask their consequences after storage. 



Until recently the cheapest form of N was usually the one chosen 

 for fertilizing orchards. It is now recognized that the form of N 

 as well as the total amount of N that is used can influence fruit 

 quality. USDA researchers first found that ammonium (NH.) forms of 

 N can intensify Ca deficiency in apples by interfering with absorp- 

 tion of Ca by roots. It has been recommended that NH. -contain ing 

 fertilizers not be applied to apple orchards before or soon after 

 bloom if growers are concerned about fruit Ca levels. 



the 



Use of Ca 

 roots and a 



(NO ) ^as 

 void! 



Is NH 



an N-source both supplies available Ca to 

 interference with Ca absorption. Our 



experiments with use of Ca (NO ) rather than NH.NO show that Ca(NO ) 

 may produce a small Increase in fruit Ca levels, but that this is 

 not enough to correct Ca deficiency if it already exists. Whether 

 the additional cost is justified by the benefit is a question for 

 growers to decide. 



Our experience leads us to conclude that the total amount of 

 N being applied to fruit trees is a more important concern to fruit 

 quality than is the form of N that is being used. 



Po tassium : K deficiency reduces growth and yield of trees and 

 severe K deficiency in apple and pear trees causes "leaf scorch", 

 a browning of the leaves. K deficiency has only a mild effect on 

 fruit quality, reducing acidity of the fruit and reducing red color- 

 ation. Excessive amounts of K in fruit are a greater danger to fruit 

 quality, since they lead to increased scald, bitter pit, and internal 

 breakdown after storage. 



Fruit accumulate large amounts of K, and large yields can remove 

 a large amount of K from an orchard. Therefore, fertilizing with 

 K is most likely to be needed after a large crop. Nevertheless, fruit 

 quality will suffer far more from excess K than from deficient K. 

 Most of the effects of high K are the result of its interference with 

 Ca in the fruit, and too much K will generally have the same effects 

 as too little Ca. 



Magnes ium : Mg deficiency can produce weak and unproductive trees, 

 and cause increased preharvest fruit drop, and its distinctive color 

 patterns on leaves have often been observed. It may be corrected by 

 application of dolomitic limestone or by foliar sprays with materials 

 such as Epsom salts. There is little evidence that either too little 

 or too much Mg directly affects fruit quality. However, excess Mg 

 interferes with Ca just as does excess K, so excessive amounts of 

 Mg will produce Ca deficiency effects in fruit. 



