THE FERTILITY OF THE SOIL 231 



from seasonal variations, must still be regarded to de- 

 pend solely upon its physical state and upon the quan- 

 tity of plant foods which the soil contains available for 

 nutritive purposes. Thus the common practice, which 

 has been so justified by experience, of heavily manur- 

 ing the soils and adding the special forms of commer- 

 cial fertilizers necessary to supply any deficiency, is 

 the only method by means of which abundant crops can 

 be produced in imperfect soils. 



HUMUS AS A MEASURE OF FEBTLLITY. 



The indeterminate position of the Bureau of Soils 

 regarding soil fertility is still further illustrated by a 

 recent publication under date of May 6, 1914, in which, 

 in tabular form, are given the yields on soils varying in 

 their percentage of humus. In North Carolina, where 

 the percentage of humus in the soil is given as 1^ per 

 cent., the yield of corn in bushels per acre is given as 

 20. In Virginia, with the humus content of the soil 

 2 1 /4 per cent., the yield is given at 30 bushels. In 

 Ohio and Illinois, with a humus content of 5 per cent, 

 in the soil, the yield is given at from 45 to 50 bushels. 



There are two or three uncertain factors in regard 

 to this case. First, there are no extensive data com- 

 piled by the Census Office of the yields of corn classi- 

 fied as to the content of humus in the soils. In the 

 second place, the content of humus in a soil is due 

 largely to its fertility, and the fertility is not due pri- 

 marily to the content of humus. The puzzling non- 

 sequential reasoning of the officials is accentuated by 

 the following statement : " The striking correlation 

 between the per cent, of vegetable matter in the soil 

 and the yield of corn in these areas investigated is an- 

 other strong link in the chain of evidence that organic 



