250 



to forms suited to the plant, and decay is slow. The black mat- 

 ter of the soil is vegetable matter in process of decay and the 

 nitrogen it contains is used as the decay progresses. 



A granite rock contains 3 to 5 per cent, of potash, but every- 

 body knows it is not soluble in water. It may also contain phos- 

 phate of lime; also useless to the plant. Soil consists of broken 

 down granite or other rock in finely divided particles. These 

 particles, acted upon by the carbonic acid of the soil, by frost 

 and air, slowly give up the potash they contain, and this is used 

 by crops. In virgin soil such preparation has been going on for 

 centuries and the stock of prepared plant food is plentiful. But 

 continued cropping uses up this stock and the time finally comes 

 when the crops must depend upon the food gradually liberated 

 from the inert forms by the atmospheric and other agencies 

 always acting. But these agencies may not work fast enough 

 and then the farmer must turn chemist and help. He plows; he 

 exposes the black matter to the air and it decays faster, supply- 

 ing nitrogen to the crop. By its decay it furnishes carbonic acid 

 which may act upon the particles of granite and set free the 

 potash and phosphoric aid. He drains his land to take water 

 out and let air in to effect these same changes. All these are 

 the operations of a chemist as much as dissolving iron or steel 

 in acid in the process of analysis is the work of a chemist. 

 These substances then are plentiful in every soil, but in forms 

 which they cannot be utilized by the plant. They may be changed 

 to available forms by natural agencies, and these may be aided by 

 the operation of tillage. 



But it may happen that with all the various agencies acting 

 and the most careful tillage either one or all of these substances 

 fail to become available as fast as they may be needed by crops. 

 This may be true of only one, and then the soil is as truly 

 exhausted as if it were true of all. Then the farmer must 

 become the analytical chemist; make analysis of his soil, find 

 out which is the wanting element, and what he must add to the 

 soil from some external source in the form of fertilizer. 



I know full well a good many farmers before me have al- 



