132 



The Principles of Fruit-growing 



"How much of this plant-food is usually furnished to 

 the orchard by leguminous plants and by feeding sup- 

 plementary foods to animals which graze upon it, and how 

 much by the fallen leaves and apples which are not 

 blown or carried off, cannot be told." 



Another calculation by Roberts shows the amount of 

 plant-food that may be expected to be carried away from 

 an acre in the fruit, and blown off in the leaves (not com- 

 puting the amount in the wood), for the period between 

 the ages of thirteen and thirty-three years of apple trees: 



"While the above results are reached by assuming a 

 given amount of apples and leaves a year in a bearing 

 orchard, and while the facts in any given case at any 

 given time may vary widely, yet it is believed that they 

 are valuable as they furnish a means of measuring in any 

 given case, with a great degree of accuracy, the amount of 

 soil-exhaustion." 



He also "shows that five bushels of apples remove 

 in round numbers eleven pounds of nitrogen, nearly one 

 pound of phosphoric acid and sixteen pounds of potash, 

 and that the leaves of a tree large enough to produce the 

 apples would contain ten pounds of nitrogen, nearly three 

 pounds of phosphoric acid and ten pounds of potash, or a 

 total of twenty-one, pounds nitrogen, three pounds phos- 

 phoric acid, twenty-six pounds potash." 



