COMPARISON OF MANURES. 215 



from stable manure, or other animal waste, they can be procured 

 in the trade, in unlimited quantit\- ; and in every degree of availa- 

 bilit}' depending on different grades of solubility ; and in the great- 

 est variety of mixtures, so as to suit an}' whim or fancy of crop 

 or crop grower. 



2. That profitable crop growing can be carried on, for many 

 years at least, with these commercial fertilizers alone. 



3. That the most evident distinction between stable manure and 

 commercial fertilizers, and the distinction upon which we should, 

 therefore, naturally base an explanation of the greater reliability of 

 the former, is its large proportion of vegetable matter, or humus- 

 forming material ; of which commercial fertilizers contain practi- 

 cally none. 



4. That soils contain, in a difficultly soluble condition, and 

 therefore not easily fed upon by the crops, large supplies of all 

 the needed elements of plant food. 



5. That humus, through its decay in the soil, furnishes car- 

 bonic acid, among other solvent agents ; and this carbonic acid ap- 

 pears to play an important part in the nourishment of crops by 

 bringing the native, insoluble stock of plant food within their easy 

 reach. 



6. That even if we add water-soluble plant food to the soil it 

 becomes largel}' insoluble before the crop can feed upon it, or needs 

 it ; therefore soluble plant food added to the soil in commercial 

 fertilizers needs also the help of the humus, finall}-, for its solu- 

 tion. 



7. That plant food in most animal and vegetable residues used 

 as manures costs much less than in commercial manures. 



8. That, in spite of the disadvantages which, under some condi- 

 tions, attend the use of commercial fertilizers, they are neverthe- 

 less a very important and necessar}' help in crop growing. 



9. That in using these fertilizers the wisest course appears to 

 be to make one's own mixtures of the raw materials, as well for 

 securing a better manure as for economy in first cost. 



Discussion. 



Professor Caldwell said, in answer to an inquiry concerning his 

 statement that soluble substances are rendered insoluble by being 

 mixed with the soil, that the nitrogen of nitrogen compounds 

 passes sooner or later into the form of nitrates, especially if the 



