THE McINTOSH DROP 9 



increasing preharvest drop from period to period (Table 3) with a greater than 

 average increase in the last four years of the study. In the other plots the dropping 

 percentages remained somewhat more constant, with only minor fluctuations 

 until the last period when again a sharp rise occurred. Four possible factors may 

 have had something to do with bringing about this trend: increasing tree age, 

 heavier fertilizer applications, weather conditions more favorable to drop, and 

 variable time of harvesting. 



Table 4 — Tree Yields and Percentage Drop by Plots and Correlation 

 BETWEEN Yield and Drop within Plots, Block E 



Average Annual Percent Correlation Coefficient 



Tree Yield (lbs.) Drop 



30.7 +.525 + . 112'' 



26.5 +.467+. 083 



25.1 -.097±.lll 

 23.3 +.205+.102 



22.6 +.160+.105 



22.2 +.389±.058 

 20.0 -.079+. 108 



Further evidence concerning the role of nitrogen follows. Dickson (4) reported 

 that a reduced nitrate supply following a minimum cultivation program was 

 associated with less severe dropping of Mcintosh. Hoffman (11) reported in- 

 creased preharvest drop under conditions where trees in sod could obtain ex- 

 cessive amounts of nitrates during the latter half of the growing season. Nitrogen 

 applications to trees on a good orchard soil over a 4-year period increased both 

 total yield and preharvest drop. The check trees were unfertilized. In one case of 

 differential treatments heavy fertilization with sulfate of ammonia was followed 

 by increased dropping percentage despite the fact that the total yield was below 

 that of the trees lightly nitrated. Southwick (29) found evidence of a correlation 

 between time of drop and amount of spur nitrogen in percentage of dry weight. 

 Here again a high nitrogen condition favored abscission. MacDaniels (16) 

 observed that fruits did not drop as readily from trees of bearing age which had 

 been moved as from normal trees. In such cases it is possible that the pruned and 

 disturbed root systems were unable to obtain the normal requirements of nitrogen, 

 moisture, and other constituents of nutrition. Such plants making slow growth 

 and having a high carbohydrate-nitrogen ratio often produce harder tissues than 

 normal or high-nitrate plants, with a resulting retarding effect on the abscission 

 process. Additional evidence on this point will be cited later. 



The author injected individual limbs with several nutrient solutions in the 

 summer of 1939. Nitrogen (in the form of urea) hastened drop. In one case, 

 for instance, the mean date of drop from a nitrogen-injected limb was fully four 

 days earlier than that from similar untreated limbs or limbs injected with non- 

 nitrogenous materials. However, it should be mentioned that in certain cases 



