LIEBIG 97 



did not produce more than fields in which this ingredient 

 was deficient. Although Liebig's theory of plant nutri- 

 tion was essentially a mineral theory, yet he understood 

 that organic matter (humus) decomposes in a soil, giving 

 rise to carbonic acid and ammonia ; and these gaseous 

 bodies are also valuable plant foods. Liebig fully 

 established the following important laws of husbandry : 



(1) A soil can be termed fertile only when it contains all the 

 materials requisite for the nutrition of plants in the required quantity 

 and in the proper form. 



(2) With every crop a portion of these ingredients is removed. A 

 part of this portion is again added from the inexhaustible store of the 

 atmosphere ; another part, however, is lost for ever if not replaced by 

 man. 



(3) The fertility of the soil remains unchanged if all the ingredients 

 of a crop are given back to the land. Such a restitution is effected by 

 manure. 



(4) The manure produced in the course of husbandry is not sufficient 

 to permanently maintain the fertility of a farm ; it lacks the constituents 

 which are annually exported in the shape of grain, hay, milk, and live 

 stock. 



These laws of Liebig form the basis of modern scientific 

 agriculture. 



Liebig was the first to treat bones with " Schwefelsaure " 

 or sulphuric acid in order to make the calcium phosphates 

 soluble (superphosphate) ; and the late Sir John B. Lawes 

 was the first to commence the manufacture of super- 

 phosphate on a large scale, both from bones and mineral 

 phosphates. 



From these early beginnings an enormous industry 



7 



