Plant- food Removed by Trees. 203 



the same as other crops, and yet the common neglect 

 of orchards seems to show that many people think 

 otherwise, or else do not think at all. In fact, the 

 depletion of the land by fruit trees is more serious 

 than by annual crops, from, the fact that plant- 

 foods are locked up for many years in the trunks 

 and branches of the trees, whilst a large part of the 

 fertilizing constituents in common crops returns to 

 the soil each year. On L the other hand, it should be 

 said that the roots of trees have a larger foraging 

 area than the roots of small crops do. This is well 

 shown in Figs. 17 and 18 (pages 160 and 162). The 

 former shows the roots running far away in the 

 poorly tilled soil in search of food, and the latter 

 shows the home -stay ing roots in the rich soil. 



Roberts has computed,* from analyses, the values 

 of nitrogen, phosphoric acid and potash taken from 

 an acre by apple trees (the trees thirty -five feet 

 apart) in twenty years, counting in ten crops of 

 fruit : 



Value. 



' Total in fruit for twenty years $147.00 



Total in leaves for twenty years 160.51 



Total in wood for life of. tree 70.00 



Grand total $377.51 



"The value of nitrogen, etc., in any given case is 

 so indefinite and variable that stress should not be 

 laid on values as given above, but on the total 

 amounts of plant -food used by the orchard. 



*Bull. 103, Cornell Eip. Station. 



