The Use of Soil Applications of Gypsum to 

 Increase Calcium Content of Apples 



William J. Bramlage, Sarah A. Weis, and John H. Baker 



Department of Plant & Soil Sciences, University of Massachusetts 



The problem of calcium (Ca) deficiency in apples is 

 well known to our readers, as is the fact that we have 

 researched various ways of alleviating this problem for 

 many years. 



There are four ways of improving Ca content of 

 apples: 



1. Orchard practices to reduce competition between 

 leaves and fruit for available Ca. 



2. Soil applications of materials to increase uptake of 

 Ca by apple tree roots. 



3. Foliar sprays of Ca-containing materials. 



4. Postharvest treatments with Ca-containing mat- 

 erials. 



In general, soil treatments have been the least 

 effective method of improving fruit Ca levels, because 

 apple roots are very poor at absorbing Ca, which is one 

 of the most abundant minerals in soil. This problem is 

 increased by the very slow movement of Ca in an apple 

 tree, resulting in slow and perhaps diluted responses to 

 whatever improvement in Ca uptake that may have 

 been achieved. 



Despite these problems, we have found that soil 

 applications of gypsum (hydrated calcium sulfate) can 

 increase apple frait Ca levels. An experiment begun by 

 Mack Drake and John Baker in 1976 first showed these 

 benefits, and another one begun by Bill Lord in 1980 

 expanded on those findings. Since the retirements of 

 Dr. Drake and Dr. Lord, we have assumed these experi- 

 ments and established a series of new ones designed to 

 answer questions raised by results from the original 

 experiments. 



Research with soil treatments to influence apple 

 nutrition progresses very slowly. First, trees respond 

 slowly to soil treatments, and second, the soil is a very 

 complicated system and when you change it, you must 

 look at long-term effects of these changes. In 1987, we 

 reported the promising results from the studies of Dr. 

 Drake and Dr. Lord, and described some of the ques- 

 tions that needed to be answered (Fruit Notes 52(2):1- 

 4). Here, we have updated those earlier findings with 

 what we have recorded during the past two years. 



In our 1987 article, we showed that 8 years of 

 annual gypsum treatments to soil beneath mature. 



seedling- rooted Cortland trees had raised fruit and leaf 

 Ca levels, decreased fruit and leaf Mg levels, and had no 

 effect on fruit and leaf Klevels. The treatments had no 

 effect on fruit firmness at harvest or after storage, but 

 reduced the occurrences of bitter pit and senescent 

 breakdown after storage. A second experiment applied 

 to young Delicious trees also showed that gypsum 

 increased Ca, decreased Mg, and had no effect on K, but 

 no consistent effects on fruit quality were yet apparent 

 at that time. We pointed out that we did not know what 

 effects the treatments were having on soil propeities, 

 that we did not know what the optimum application 

 rate was, and that we did not know the economics of 

 gypsum treatments. 



Currently, we have three long-term gypsum ex- 

 periments in progress. The first is a continuation of the 

 experiment begun by Dr. Lord in 1980, using a block of 

 Sturdeespur Delicious trees on MM. 106 planted in 

 1972. Trees in this block were given 0, 50, or 100 lbs. of 

 gypsum (0, 0.3, and 0.6 lbs. per sq. ft.) each April 

 through 1985, v^ath the gypsum spread beneath the 

 tree canopy. By 1985, it was apparent that both 50-lb. 

 and 100-lb. application rates were having the same 

 effect, so the 100-lb. rate was discontinued to deter- 

 mine how long effects would last after a gypsum treat- 

 ment was ended. 



The second experiment was established in a block 

 of mature Cortland trees on M.7 rootstock planted 

 about 1962. These trees have a severe Ca deficiency, 

 and their fruit always develop high rates of bitter pit 

 and senescent breakdown. The objective was to see 

 what role gypsum treatments might play in trying to 

 control a chronic Ca-deficiency situation. Annual 

 applications of 0, 40, or 80 lbs. of gypsum (0, 0.25, and 

 0.5 lbs. per sq. ft.) beneath the tree canopy are made in 

 April or May. The experiment was begun in 1986 and 

 thus is in its fourth year. 



The third experiment was established in 1987 in a 

 block of Cortland trees on M.7a rootstock planted in 

 1981. Trees received applications of 0, 8, 16, 24, 32, 40, 

 or 48 lbs. of gypsum (0, 0. 1, 0.2, 0.3, 0.4, 0.5, and 0.6 lbs. 

 per sq. ft.) in April, in an attempt to learn the optimum 

 rate of application. 



FmU Notes, Fall, 1989 



