Percent of control 



125 



120 



116 



110 



106 



101 



S6 



BO 



86 



80 



Percent of control 



Fruit 



High rate 

 diaoonllntMd 



88 



76'— 

 80 



81 82 83 84 88 88 87 88 



Year 



Figure 1. Effects of low (50 Ibs./tree) and high (100 Ibs./tree) rates of gypsum, applied annually, on leaf 

 and fruit mineral composition of Delicious. The high rate was discontinued after 1985. 



The soil type in these blocks is generally a Scituate 

 fine sandy loam, although depth to hardpan and spe- 

 cific soil characteristics varies somewhat among the 

 blocks. 



Effects on Leaves and Fruit 



In the Delicious experiment, we continue to see the 

 effects of gypsum on leaf and fruit mineral composition 

 that we repoi-ted earlier, that is, gypsum significantly 

 increases leaf and fruit Ca and decreases leaf and fruit 

 Mg (Figure 1), but has no effect on leaf and fruit K (data 

 not shown). The effects were quite consistent from 

 year to year, with about a 20% increase in leaf Ca and 

 a 10% increase in fruit Ca, and a 20% decrease in leaf 

 Mg and a 5% decrease in fruit Mg each year after 

 responses were established. This means that the re- 

 sponse is very reliable, and also that you can get only so 

 much response from a gypsum treatment: once the 

 response is established, it does not get bigger as you 

 continue to apply gypsum from year to year. It is also 

 clear that it takes time for the tree to respond to 

 gypsum treatments — in this case, it took 3 years after 

 treatments began before the responses were estab- 

 lished. 



In the trees where gypsum applications were dis- 

 continued in 1985, it can be seen that levels of leaf and 



fruit Ca and Mg continued to show the gypsum effect 

 for at least two years. In 1988, the third year, it 

 appeared that levels might be starting to change, but 

 we should have a much better picture of this after the 

 1989 analyses are completed. It may be that 3 years 

 represents the time needed for Ca to move from the 

 roots to the fruit in these trees, since it took this long to 

 see benefits of gypsum treatments, and perhaps this 

 long to see any result of ending the treatment. 



The gypsum treatments had a very consistent ef- 

 fect on the occurrence of bitter pit in these fruit (Figure 

 2). Once the treatment effects were established, 5 to 

 10% less of the crop has developed bitter pit after 

 storage in the samples taken from gypsum-treated 

 trees, except in 1986 when no bitter pit developed in 

 any fruit. Again, as with the mineral analyses, it is 

 clear that only so much could be done to alleviate Ca 

 deficiency through gypsum treatments. They did not 

 work magic! 



In the experiment with mature, Ca-deficient Cort- 

 land trees, leaf Ca wtis increased and leaf Mg was 

 decreased in the third year of treatment (Figure 3), as 

 with the Delicious. However, there was no effect on 

 fruit Ca or Mg, or on fruit quality, during the first three 

 years. Since these trees were larger than the Delicious 

 trees at the time their experiments were established, it 

 may be taking longer for the Ca to travel from root to 



FmifAtoto, Fall, 1989 



