MANURES. 193 



ammonia and other substances, which, while they feed the crop, 

 add greatly to the solvent power of water ; as it rots down, its 

 coarser parts are changed into compounds which are very active 

 absorbers or fixers of ammonia ; and, by reason of its fibrous 

 texture, it loosens heavy clays, and binds together blowy sands, 

 while its decomposition produces heat which warms the soil, and 

 its power of absorbing moisture from the air keeps it moist. 



The action of all manures is so complex, and, in some respects, 

 so imperfectly understood, that it is not easy to classify them by 

 any system that is free from objection, and as this is a book of 

 practice rather than of principles, it will be best to consider the 

 different common fertilizers in order, leaving the question of their 

 classification to more purely scientific essays. The first in order, 

 in the agriculture of all countries where domestic animals arc 

 largely kept, is, of course, 



FARM-YARD MANURE. 



This consists of the undigested parts of food ; of those con- 

 stituents of the animal's body which, being expended in the 

 vital processes, are discarded in the urine and dung j and of the 

 straw, etc., used for litter. The first two of these constituents 

 always bear a direct relation to the food, and their relative value 

 may be more nearly estimated. The third, the litter, is very 

 variable in kind and in quantity, according as we use much or 

 little of straw, corn-stalks, leaves, peat, sea-weed, beach-sand, 

 etc., etc. 



Except when peat, sand, etc., are used, stable manure contains 

 nothing but what has already formed a part of plants, and it con- 

 tains every ingredient that plants require for their growth. This, 

 however, states but one half of the question. The other half 

 — and a very important one it is — is as follows : a given quantity 

 of farm-yard manure does not contain all that is needed to produce 

 the same quantity of vegetable matter that constituted the food 

 and litter of the animals by which it was produced. 



A part of their food has passed into the air in the carbonic 



