COMMERCIAL FERTILIZER MATERIALS 443 



obtained from the soil but pointing out that they were ab- 

 solutely essential for plant growth, Liebig/ in Germany, at 

 about the middle of the nineteenth century, emphasized still 

 more strongly the importance of minerals to plants, refuting 

 the theory, at that time current, that plants obtained all of 

 their carbon from the soil organic matter. While he showed 

 the importance of potash and phosphoric acid in manures, he 

 failed to appreciate the value of nitrogenous materials, hold- 

 ing that the soil received sufficient ammonia in rain-water. 

 The true conception of the necessity of supplying nitrogen 

 in some form was definitely established in an experimental 

 way in 1857 by Lawes, Gilbert and Pugh ^ of the Rothamsted 

 Experiment Station, England. The extreme care used by 

 these investigators caused them to sterilize the soil with which 

 they were working. They thus failed to discover the utiliza- 

 tion of free atmospheric nitrogen by legumes. This phe- 

 nomenon, so important in practical agriculture, was explained 

 by Hellriegel and "Wilforth in 1886. 



Between 1840 and 1850 Sir John Lawes placed the manu- 

 facture of superphosphates on a commercial basis by treating 

 bones and coprolites with sulfuric acid. At about this time 

 the importation into Europe of Peruvian guano and sodium 

 nitrate began. The commercial fertilizers industry, which 

 has now attained such importance in practical agriculture, 

 may be considered as dating from this period. 



243. Commercial fertilizers. — ^Although the commercial 

 fertilizer industry is but little more than seventy years old, 

 the sale of fertilizers in this country at the present time 

 amounts to millions of dollars annually. Animal refuse and 



^Liebig, J. Justus von, Principles of Agricultural Chemistry with 

 Special Reference to the Late Besearches Made in England; London, 

 1855, Also, Chemistry in Its Applications to Agriculture and Physiology ; 

 New York, 1856. 



* Lawes, J. B., G-ilbert, J. H., and Pugh, E., On the Sources of the 

 Nitrogen of Vegetation, w%th Special Reference to the Question Whether 

 Plants Assimilate Free or UncomMned Nitrogen; Eothamsted Memoirs, 

 Vol. 1, No. 1, 1862. 



