FARM MANURES 



597 



manure is due to the mycelium, which penetrates in all 

 directions and uses up the valuable constituents. Manure 

 thus affected is of little value either as plant-food or as a 

 soil amendment. 



501. Waste of farm manures. Any system of agri- 

 culture, in order to be permanent, must arrange for the 

 addition of as much plant-food as is removed in the crop 

 and the drainage water combined. Even if all of the 

 crop were returned to the soil, a permanent system of 

 agriculture would fall far short of being established, since 

 at least as much plant-food is removed by leaching as by 

 cropping. As a matter of fact, it is not even possible to 

 return to the land as farm manure all the constituents 

 taken off in the crop, due to the ease with which loss occurs. 

 These losses may be grouped under two general heads : 

 (1) those that occur as the food passes through the animal ; 

 and (2) those that are due to leaching and fermentation. 



502. Losses due to digestion. A certain quantity of 

 material is necessarily taken from the original food as it 

 passes through the animal. This loss falls most heavily 

 on the organic matter and only slightly on the mineral 

 constituents. Wolff * presents the following figures aver- 

 aged from all classes of animals : 



PERCENTAGE OF ORIGINAL FOOD CONSTITUENTS RECOVERED 

 IN FRESH MANURE 



1 Aikman, C. M. Manures and Manuring, pp. 228 and 232. 

 Edinburgh and London. 1910. 



