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A very small amount of Ca moves into the fruits in compari- 

 son to the amounts of Mg , N, P and K. Nevertheless the presence 

 of adequate Ca in the soil does not assure sufficient uptake by 

 the tree and translocation especially to the fruit; nor does 

 adequate Ca in the tree ensure optimum Ca levels in the fruit 

 because there is competition between leaves and fruits for this 

 clement and leaves are a stronger competitor. The high leaf/fruit 

 ratio on light cropping trees tends to increase fruit size which 

 dilutes the Ca content of the fruit. In contrast, heavy cropping 

 reduces the excessive vegetative demand for Ca and makes this 

 element more available to the fruit. Fruit size may be reduced 

 by heavy cropping; smaller fruit have more Ca than larger fruit. 



Fruits which constitute the greater part of the total dry 

 matter iii fruiting trees, have a much lower N concentration in 

 their dry matter than is found in the new growth of non-fruiting 

 or light- fruit ing trees. Therefore, N deficiency is most likely 

 to occur on non- or light - fruiting trees which have large demand 

 for this element for root and top growth, than on a heavy- cropping 

 tree. Mg tends to accumulate at a uniform rate in the fruit and 

 any reduction in Ca accumulation is reflected by a higher ratio 

 of Mg and/or K to Ca . 



It is clear from above that the nutrient needs differ greatly 

 for the non- or light-cropping tree in comparison to the heavy- 

 cropping tree. Except for uptake of K, which is very mobile, the 

 uptake and transport of nutrients is suppressed by heavy fruiting. 

 Also with the exception of K the demands for the other nutrients 

 is much less in heavily bearing trees in comparison to those 

 with no crop or a light crop. What does this mean in regard to 

 fertilization? 



Young non-bearing trees require heavy fertilization with N 

 to stimulate growth and only moderate amounts of K, and P is not 

 considered a limiting factor in orchard soils. N levels should be 

 reduced in bearing trees (1.80 - 2.00% "leaf N is optimum for most 

 varieties) and moderate levels of K, Mg , B and high levels of 

 Ca should be maintained. Unfortunately, sufficiently high levels 

 of Ca generally are possible only by spray applications of CaCl^. 

 And, as discussed later, soil management practices may have greater 

 influence on tree nutrition than fertilization. 



Interaction Among Elements 



Ca deficiency can occur independently of its availability in 

 the soil because excess K can affect uptake, and after uptake the 

 distribution within the tree. Thus, the Ca/K ratio may be as 

 important as the availability of the Ca. Researchers in South Africa 

 believe that leaf Ca level of 1.60% and a K/Ca ratio of 0.65 are 

 necessary to minimize the incidence of bitter pit under their 

 conditions . 



