THE YEAST OF THE SOIL. 19 



the lower orders of life which it contains, the bacteria and other 

 unseen forces, to the end that we may know what each contributes 

 to the upbuilding, not alone of the soil, but of the crop life above the 

 soil, upon which all higher forms of life and acti\'ity depend. 



Potential Fertility. 



Chemistry teaches us that plants are composed of certain fixed 

 elements which are supplied by the soil and the air. It further 

 teaches that while there is an abundant supply, yet we have ex- 

 hausted the three leading elements, nitrogen, phosphoric acid, and 

 potash, in available forms; that so-called barren or unproductive 

 soils may be rich in plant food elements but that these elements are 

 so locked up as to be of little value to the commercial farmer whose 

 chief concern is quick crops for quick returns. In other words, 

 the available plant food (nitrogen, phosphoric acid, and potash) has 

 been exhausted, lea^^ng only the unavailable or what is known as 

 the potential fertility which, by the slow processses of nature, is 

 yielded up too slowly to be depended upon by the commercial 

 farmer. 



It has been known for a long time that practically all tillable soils 

 are rich in all plant food elements, and yet many of them are barren, 

 and most of them will not produce profitable crops without the aid 

 of manure or fertilizer. Prof. Frederick D. Chester, of the Delaware 

 Agricultural College, states: 



"An average of the results of 49 analyses of the tyj^ical soils of 

 the United States showed per acre for the first eight inches of surface, 

 2600 lbs. of nitrogen, 4800 lbs. of phosphoric acid, and 13,400 lbs. 

 of potash. The average yield of wheat in the United States is 14 

 bushels per acre. Such a crop will remove 29.7 lbs. of nitrogen, 

 9.5 lbs. of phosphoric acid and 13.7 lbs. of potash. 



"Now, if all the potential nitrogen, phosphoric acid and potash 

 could be rendered available, there is present in such an average soil, 

 in the first eight inches, enough nitrogen to last 90 years, enough 

 phosphoric acid for 500 years, and enough potash for 1000 years. 



"This is what is meant by potential soil fertility, and yet such a 

 soil possessing this same high potential fertility may, under certain 



