39 



PARAGRAPH XIII. 



SOIL REQUIREMENTS IN FORESTRY. 



The trees take from the soil a smaller amount of mineral matter 

 than do the field crops. 



In the field crops we remove from the farms a large amount 

 of phosphates, nitrates, and potash, contained in the seeds (small 

 grain, corn, and cotton). In the case of the forests, not the seeds 

 of the trees, but the fibre is removed, which consists almost 

 exclusively of carbo-hydrates. 



What mineral food the trees may take from the soil is obtained 

 from the lower rather than from the upper strata of soil. 



The disintegration of the underlying rock may keep pace with 

 the exhaustion by the trees of the inorganic matter in the soil. 



Ebermeyer finds that the yearly growth of a forest takes from 

 the soil 540/0 of the mineral substances which an ordinary field 

 crop would require. 46 0/0 out of the 54 0/0 used by the trees 

 is, however,, restored to the ground when the leaves or needles 

 are dropped, so that only 80/0 is actually converted into wood 

 fibre. In other words: The forest withdraws from the soil 

 by 121/2 years growth as much fertility as does the farm crop 

 in one year. 



It is a well-known fact that trees can be grown on soil which 

 is too poor for agriculture. The exhausted farms in the south 

 are redeemed almost invariably by the re-establishment, spon- 

 taneously, of the woods. 



The following tabular statement shows the requirements of 

 inorganic matter, per acre per year, on the farm and in the forest: 



It should not be assumed, however, that the trees are in- 

 sensitive to the quality of the soil: the contrary is the case. 



