THE WAY YOU FERTILIZE YOUR FRUIT TREES 

 CAN AFFECT THE QUALITY OF THE FRUIT YOU HARVEST 



William J. Bramlage, Mack Drake, and William J. Lord 

 Department of Plant and Soil Sciences 



In the first half of this century, studies of the fertilizer 

 needs of fruit trees focussed on what was needed to maximize tree 

 growth and fruit yield. In the last couple of decades, however, 

 attention has turned toward the effects of nutrition on the quality 

 of harvested fruit. While the effects of calcium (Ca) deficiency 

 have been the driving force behind the reconsideration of mineral 

 needs, effects of nitrogen (N), potassium (K) , magnesium (Mg), 

 boron (B) and phosphorus (P) levels in fruit on their postharvest 

 quality have been noted. 



It is clear that the mineral composition of fruit at harvest 

 is an extremely important factor in determining how well fruit will 

 keep after harvest. Most of the research on this problem has been 

 on apples and to a lesser extent, pears, but presumably the same 

 relationships also have some relevance to postharvest problems with 

 other kinds of fruit. It seems appropriate to review these relation- 

 ships between fruit nutrition and fruit quality as we enter into a 

 new growing season. 



Calcium : In 1936 bitter pit was found to be related to low Ca 

 levels in apples. Thirty years later it could still be stated that 

 "Inspite of the very low Ca status of many orchard so ils ... there 

 have been few reports of direct responses by bearing apple trees to 

 Ca..." ( Temperate to Tropical Fruit Nutrition , Norman F. Childers, 

 Editor.) Today, however, there is strong concern about Ca levels 

 in apples and pears just about anywhere in the world that they are 

 grown . 



At first, this concern was directed at bitter pit and cork spot 

 but today we know that many physiological disorders may be at least 

 partly related to low Ca levels in the fruit. In warmer fruit grow- 

 ing areas, cork spot and bitter pit remain the most serious effects 

 of low Ca, but in cooler areas various forms of internal breakdown 

 are the most serious Ca-def ic iency problem. In British Columbia, 

 Canada, the 'Spartan' apple industry was almost destroyed by break- 

 down problems before methods of raising fruit Ca levels were success- 

 fully developed. 



Many approaches have been taken to try to raise fruit Ca levels. 

 Since Ca is less available in acid soils, regular liming programs are 

 essential in areas of low soil pH. Calcitic lime is more soluble 

 and is preferable to dolomitic lime unless Mg deficiency exists, 

 since dolomitic lime supplies little available Ca to the soil. Use 

 of calcium nitrate (Ca(NO ) ) as a source of fertilizer N is often 

 recommended, and we have round that it can provide a small increase 

 in fruit Ca levels. In areas where soil is droughty, irrigation is 



