212 FUNDAMENTALS OF FRUIT PRODUCTION 



meeting the trees' requirements for moisture when nitrogenous fertilizers 

 are used. It also raises a series of interesting and important, but wholly 

 unanswered, questions as to the relative influence different fertilizers may 

 have on different parts of the tree — for example, roots, leaves, fruit. It 

 is clear that, at present, there are no means of increasing the size of fruit 

 directly through the use of any particular fertilizer. Fertilizers can lead 

 to the production of larger fruit only as they lead to increased vegetative 

 growth and the consequently increased amounts of manufactured foods 

 and as they lead to a greater extension of the root system and to a conse- 

 quently greater intake of water or in still other indirect ways. 



Influence of Nitrogen on Color of Fruit. — There has been much dis- 

 cussion in pomological Hterature concerning the use of fertilizers for 

 aiding the coloration of fruits and applications of potash and phosphoric 

 acid have been rather generally recommended for this purpose. Hedrick 

 was one of the first to submit experimental data bearing on this question. 

 After a 10-year trial with several varieties in an old New York apple 

 orchard growing in a rather heavy clay he concluded that no influence 

 on color of fruit could be ascribed to the potash or phosphoric acid 

 \/^ which had been used.^" Stewart ^''^ in summarizing the results of his k 

 work with apples in Pennsylvania says: "None of the fertilizer treat- 

 ments has resulted in any marked improvement in color. Slight 

 and irregular benefits are shown by potash and by some of the phosphate 

 applications, but nothing of any importance ..." Some of the graphs 

 in Figs. 25 and 26, plotted from data presented by Stewart, furnish clear 

 evidence in support of his conclusions. Alderman^ reports a reduction of i^ 

 the red color in peaches accompanying the use of nitrogenous fertilizers 

 and ascribes it to late maturity and to increased density of the foliage. 

 Conversely, some slight increases in color from the use of potash or phos- 

 phoric acid he ascribes to the slight checking effect these materials some- 

 times have on vegetative growth. It is significant that the curves 

 representing average influence of fertilizers on color are almost exactly 

 the reverse of those representing their influence on vegetative growth. . 

 In other words, the two phenomena, those of color formation and new 

 vegetative growth, are negatively correlated. 



Influence of Nitrogen on Yield. — In general the tendency of nitrog- 

 enous fertilizers is to increase vegetative growth, promote the formation 

 of fruit buds, increase the percentage of flowers setting fruit and lead 

 to larger size in the individual fruits. It is inevitable therefore that their 

 general influence must be greatly to increase yields. Many data might 

 be presented in support of this general conclusion. Those given in 

 Tables 71 and 72 represent some of the more striking results that have 

 been obtained; these, however, have been duplicated in orchards in 

 many parts of the country. Table 73 is particularly interesting as 

 emphasizing the importance of nitrogen compared with the other nutrient 



