6 MASS. EXPERIMENT STATION BULLETIN 372 



work, however, has been done with late or preharvest drop. Blake^ suggested 

 that high temperature leading to rapid carbohydrate respiration may be a sig- 

 nificant factor in bringing about fruit drop in New Jersey before and during the 

 harvest period. In Rhode Island, Christopher' observed variable dropping 

 according to spray materials used, the amount of drop depending on the causticity 

 of the spray. At Amherst it was found that late season defoliation sometimes 

 caused earlier dropping of Mcintosh apples. In any one section, there seems to be 

 a negative correlation between altitude and the severity of Mcintosh drop. A 

 favorable response to phosphate fertilizer was noted by Harrington* in the 

 Bitter Root Valley of Montana. Fertilization with nitrogen alone seemed to cause 

 severe dropping while the addition of phosphorus resulted in "much better stick- 

 ing qualities." However, there is not sufficient evidence to prove that this is 

 generally true. Increased dropping due to boron deficiency conditions and ex- 

 cessively high lime in the soil has been noted in Canada according to Davis^ 

 and Mann.^ Premature fruit drop has been attributed from time to time to un- 

 desirable physical characteristics of soil, but in New Hampshire differences in 

 soil structure could not be correlated with the amount of dropping (24). 



Effect of Soil Fertility 



In 1936, Shaw and Southwick (26) reported evidence of increased dropping 

 on heavily mulched plots where soil nitrates were found in abundance even during 

 the fall and winter months. Later, large amounts of available potassium also 

 were found to be present (27). No mineral fertilizers had been applied to either 

 plot up to 1933 when nitrogen was given to the trees under cultivation. Over a 

 continuous period of sixteen years the mulched trees dropped an average of 27 

 percent compared with 16 percent for the trees under cultivation (Table 2). 

 The difference between the two values is highly significant, the probability of 

 obtaining such a difference due to chance alone being negligible. The severity 

 of drop increased steadily over this period so that in the last few years from 35 

 to 50 percent drop was a common occurrence. However, it should be mentioned 

 that despite the higher percentage of drop, actually more bushels of fruit were 

 hand-picked from the mulched trees because of the higher yields. 



Another illustration of the effects of fertilizer and soil treatment on dropping 

 has been given in Station Block E, again over a 16-year period. This block 

 consists of seven plots and there are ten 27-year-old Mcintosh trees on each plot, 

 the interplanted Baldwins having been removed in 1936. Yield and drop data 

 are given in Table 3 on the basis of 4-year periods. Percentages of drop are also 

 given for the 8-year period from 1930-1937 and are treated statistically. 



Sixty-one trees have been used in these records. Approximately one-fourth 

 of the total crop produced over this 16-year period consisted of dropped fruit 

 despite the rather poor yield record. From 1922 to 1929, dropping was not very 

 severe but was more pronounced on the nitrogen plots. Some treatments have 

 been changed since 1929 and during the period 1930-1937 a heavier fertilization 



2m. a. Blake. Correspondence, 1937. 

 3E. p. Christopher. Correspondence. 1936. 

 *F. M. Harrington. Correspondence, 1938. 

 ^M. B. Davis. Correspondence, 1938. 

 ^A. J. Mann. Correspondence, 1938. 



