8 THE MANURE HEAP [CH. 



becoming increasingly important. Thus, the following is the 

 order of merit for some well-known feeding stuffs: 



Decorticated cotton cake 

 Linseed cake ... 

 Coco-nut cake 

 Palm-nut cake 



Oats 



Oat straw 

 Swedes 



But composition is not the only factor : digestibility is equally 

 important. It so happens that the substances which the animal 

 cannot digest also prove very difficult for the soil bacteria to 

 attack, and so when they reach the soil they do not easily undergo 

 conversion into plant food. These undigested substances form 

 the faeces which are therefore the least valuable part of the manure. 

 The digestible part of the food, on the other hand, is easily attacked 

 by soil bacteria, and forms the best part of the manure. Of course 

 if the animal kept all that he digested there would be none of it 

 in the manure heap, but fortunately he does not. The oils, 

 carbohydrates, and the carbonaceous part of the albuminoids are 

 partly stored as fat and partly breathed out, but these are not the 

 valuable fertilising constituents. The really useful fertilisers, the 

 nitrogen and potash, are not stored except to a slight extent, and 

 are not breathed out: they are excreted in the urine. This, 

 therefore, represents the most valuable part of the manure. 



Fatting beasts retain least of the nitrogen, phosphates, and 

 potash in the food they digest, and, as they get the richest food, 

 their urine is the richest on the farm. 



Growing stock retain more, and therefore their urine is poorer. 

 Milking cattle retain most, and on equal rations would give the 

 poorest urine ; but as they usually receive considerable quantities 

 of highly nitrogenous food their urine is often very rich. 



For 100 parts of nitrogen, phosphoric acid and potash in the 

 food the following have been found in the dung: 



