treatments can improve fruit Ca levels and fruit qual- 

 ity. It is also clear, however, that benefits are limited. 

 Figures 1 and 2 convincingly demonstrate that only a 

 relatively modest improvement can be achieved, but 

 these Figures also show that a fruit grower can count 

 on this level of benefit once treatment responses are 

 established. Thus, it appears that gypsum treatments 

 have a role in trying to control Ca deficiency in apples, 

 but they are not a solution to Ca deficiency, a problem 

 that is a part of modern apple production. 



We are still far from knowing what is the optimum 

 treatment of gypsum. It appears that we have applied 

 much higher rates than needed in our experiments to 

 date, but several more years of data will be needed to 

 clarify this. Likewise, we cannot tell yet whether or not 

 annual treatments are needed. Even though treat- 

 ments greatly increased exchangeable Ca in the soil, 

 one cannot assume that trees can continue to benefit 

 from this after annual treatment ceases. 



It is clear from these data that there is a long delay 

 after gypsum is applied until the fruit begin to show 

 increased Ca levels and improved quality. Results 

 presented here suggest that at least two years are 

 required, and that in large trees even three years may 

 not be a long enough time. Responses of finiit to 

 gypsum come slowly! 



It is also clear that a price is to be paid for improved 

 Ca levels in fruit: the reduction in leaf Mg. In the 

 results shown here, the reduction was small and did 

 not increase over time, although in Dr. Drake's original 

 gypsum experiment, the reduction in leaf Mg became 

 greater each year of treatment. The severe reduction in 

 soil exchangeable K is also troubling. Perhaps in other 

 orchards, leaf K might be reduced. There is also the 

 possibility that some other element, such as manga- 

 nese might be influenced by such large effects on soil 



chemistry. Thus, it is imperative that an orchardist 

 who tries gypsum treatments employ a careful leaf 

 analysis program to monitor the mineral nutrition of 

 the trees. 



It should be noted that gypsum is well known to 

 improve the physical properties of soil, and in particu- 

 lar to improve water penetration. Thus, gypsum may 

 help maintain good soil properties, especially in herbi- 

 cide strips where soils can lose their structure over 

 time. 



It should be pointed out also that gypsum is not a 

 substitute for lime, and vice versa. As seen in Table 2, 

 gypsum did not change pH, so it did not change the 

 liming needs of the soil. Gypsum is much more water 

 soluble than lime, and quickly penetrates through the 

 soil profile (Figure 4). Lime, in contrast, quickly affects 

 only the soil area where it was applied, moving only 

 very slowly down through the soil. If an orchardist is 

 using gypsum, then liming should be done with only 

 dolomitic limestone, to help offset the loss of soil Mg 

 due to gypsum (Figure 4). 



We cannot judge the economics of gypsum treat- 

 ments from our experiments. At this point, we do not 

 know what is the optimum rate of application, or 

 whether or not annual treatment is required. Also, we 

 do not know what is the most economical materied to 

 apply. 



In our experiments, we have used mined, ground 

 white gypsum, which is relatively expensive. There are 

 other grades of mined gypsum, which, because they are 

 not white, cannot be used in wallboard and thus are 

 less expensive. Also, there are vast quantities of mate- 

 rials available at many power plants that are the result 

 of purging smokestacks of sulfur emissions. A series of 

 studies have suggested that these materials may be as 

 effective as mined gypsum when applied to the soils. 

 We have not used any of these materials, but they may 

 be available at little or no cost other than transporta- 

 tion. Indeed, use in orchards may be a desirable way of 

 disposing of such waste materials. 



Clearly, many questions about use of gypsum or 

 gypsum-like materials to improve fruit Ca levels re- 

 main to be answered. However, our results strongly 

 suggest that treatments can produce consistent, albeit 

 modest, improvements in fruit Ca and quality. Such 

 treatments will not solve the Ca-problem in apples, but 

 may be a part of the program needed to cope with Ca 

 deficiency, which is such a general part of modern apple 

 production. 



Acknowledgement 



We wish to thank Agway, Inc., Syracuse, New 

 York, for their financial support during the course of 

 these experiment. 



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Fruit Notes, Fall, 1989 



