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 erops returns to 
the soil each year. On 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-staying 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.......... erty ot tediere eS $147.00 
Total in leaves for twenty years..............-eee eee 160.51 
Total in wood for life of tree... ..04scscvs sean reece ee 70.00 
Grand total. ...... see cece eee eee eee eee eee $377.51 
“The value of nitrogen, ete., 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 Exp. Station. 
