10 



EFFECTS OF FERTILIZATION ON APPLE QUALITY 



William J. Lord 



Department of Plant and Soil Sciences 



University of Massachusetts 



It is necessary to produce apples with high quality, and many orchard 

 factors can affect quality. However, one of the most important and easiest to 

 alter is nutrition. Below are presented some of the effects of fertilization 

 on fruit quality. 



Calcium 



Initially, the concern about low fruit calcium was directed at bitter pit 

 and cork spot, but today many other physiological disorders have been at least 

 partly related to low calcium levels in the fruit. In warmer fruit growing 

 areas cork spot and bitter pit remain the most serious effects of low calcium; 

 but in cooler areas various forms of internal breakdown are the most serious 

 calcium-deficiency problems. 



Nitrogen 



Excessive amounts of nitrogen in the tree and fruit can severely reduce 

 fruit quality. The vigorous growth that nitrogen encourages results in a lower 

 calcium level in the fruit. Moreover, the high nitrogen fruit tend to be 

 larger, greener, and softer; are more subject to preharvest drop; and have more 

 cork spot and bitter pit. These fruit also tend to develop greater am.ounts of 

 scald, bitter pit, internal browning, and internal breakdown during and after 

 storage. 



Potassium 



Potassium deficiency has only a mild effect on fruit quality, reducing the 

 acidity of the fruit and reducing red coloration. Excessive amounts of 

 potassium in fruit are a greater danger to fruit quality, since they lead to 

 increased scald, bitter pit, and internal breakdown after storage. 



Magnesium 



There is little evidence that either too little or too much magnesium 

 directly affects fruit quality. However, excess magnesium interferes with 

 calcium just as does excess potassium, so excessive amounts of magnesium may 

 produce calcium deficiency effects in fruit. 



Phosphorus 



Phosphorus deficiency can reduce tree growth and yield, and in several 

 parts of the world it also has been shown to cause increased amounts of 



