206 The Principles of Fruit-growing. 



of twenty -one pounds nitrogen, three pounds phos- 

 phoric acid, twenty -six pounds potash." 



"As a clearer comprehension is had by comparing 

 unfamiliar things with familiar things, a table follows 

 which gives in brief the soil exhaustion which is 

 likely to occur from a continuous twenty -year wheat 

 production. Here, again, an average yield has been 

 assumed which, while approximately correct for New 

 York, may be wide of the mark in some states where 

 the average yield of wheat falls to eight or ten bush- 

 els per acre. 



"The following tables show the amounts and 

 values of the fertilizing ingredients removed by wheat 

 (grain and straw) in twenty years' continuous crop- 

 ping, assuming an average yield of fifteen bushels per 

 acre and seven pounds of straw to three pounds of 

 grain : 



"COMPOSITION OF WHEAT AND STRAW. 



Water, Nitrogen, Phos. acid, Potash, 



per cent. per cent. per cent. per cent. 



Grain 14.75 2.36 .89 .61 



Straw 12.56 .559 .12 .51 



"AMOUNTS AND VALUE OP PLANT-FOOD REMOVED IN ONE YEAR 

 AND IN TWENTY YEARS. 



Nitrogen, Phos, acid, Potash, Total 



Ibs. Ibs. Ibs. value. 



Grain, 1 year 21.24 8.01 5.49 $3.99 



Grain, 20 years 424.80 160.20 109.80 79.86 



Straw, 1 year 11.74 2.52 10.71 2.42 



Straw, 20 years 234.78 50.40 214.20 48.37 



Total value in wheat, grain and straw for 20 jears. $128.23 

 Total value in apple, fruit and leaves for 20 years. . 207.45 



"The above table shows that the orchard requires, 



