Fineness 



assimilable than they seem, they would not buy 

 them. It would be more practical to convince 

 ourselves that they are no more useful to us than 

 to anybody else, and leave them alone. The worst 

 of all is that things are often sold as manures 

 which are obviously coarse, inassimilable, or nearly 

 inassimilable products, and which are not worth 

 much more as a matter of fact than the simply 

 neutral materials which are sometimes sold as 

 manure. 



The nature of the soil influences the assimila- 

 bility of certain manures. For example, acid soils 

 will facilitate the assimilation of tricalcic phos- 

 phates, whereas in the same soils sulphate of 

 ammonia will be less active. 



Certain plants thrive best on certain manures, 

 which are therefore of a greater assimilability for 

 those plants. Oats, for example, utilise nitrates 

 most easily and most rapidly. Some manures 

 become more assimilable according to the treat- 

 ment they receive. Thus bones are more assimi- 

 lable after fermentation, and tricalcic phosphates 

 after treatment with sulphuric acid ; but by these 

 processes the manures suffer chemical changes and 

 are no longer entirely the same. 



Artificial chemical manures are generally con- 

 centrated. That is to say they contain in a little 

 weight a great quantity of fertilising matter. Thus 

 when one uses a hundredweight of superphosphate, 

 one has given to the soil much more phosphoric acid 

 than by using a cartload of farmyard manure. 

 These manures are very easily handled, require 

 little time for their distribution, are easily 



^5 



