SOILS AND FERTILIZERS 421 



While manures may lose a large per cent of their valuable con- 

 stituents, yet they may be worth more per ton than they were before 

 the loss occurred; because the plant foods remaining are concen- 

 trated into a less quantity of material. 



Where it is practicable to haul the manure from the stalls and 

 pens and spread it on the field at short intervals, the losses of valu- 

 able constituents need not be very great, but when, as in winter, the 

 manure must be stored for some time the difficulties of preservation 

 are greatly increased. 



Under these conditions, deterioration of manure results from 

 two chief causes: (1) Fermentation, whereby a certain amount of 

 the nitrogen is lost, and (2) weathering or leaching, which involves 

 a loss of the soluble fertilizing constituents, including potash and 

 phosphoric acid as well as nitrogen. 



Fermentation of Manure. The fermentation of manure is due 

 to the action of minute microscopic organisms which belong to two 

 great classes: (1) Those which require an abundant supply of air 

 (oxygen) and which die when deprived of oxygen Known as 

 aerobic ferments; and (2) those which grow without oxygen and 

 die when exposed to it known as anaerobic ferments. 



The decomposition observed in the manure heap is due as a 

 rule to the combined action of these two classes of ferments. On 

 the outer surface of the heap, where the air circulates freely, the 

 first class (aerobic) is active, while in the interior of the heap, 

 where the supply of air is limited, the fermentation is due to the 

 anaerobic ferments. The latter soon run their course and cease to 

 exist. Their function seems to be principally to break up the more 

 complex substances of the manure and prepare them for the further 

 action of the aerobic ferments, which finally convert them into 

 simpler compounds, such as water, carbon dioxid, and marsh gas. 



Where the manure is compacted (as in deep stalls, for instance) 

 the carbon dioxid formed by fermentation soon permeates the mass 

 so completely as to entirely exclude the air, thus arresting fermenta- 

 tion. In loose heaps into which air is freely admitted fermentation 

 of the aerobic form may go on indefinitely. 



The fermentations of manure are very complex and vary ac- 

 cording to circumstances. The principal conditions affecting these 

 processes are (1) temperature, (2) supply of air as determined by 

 compactness of heap, (3) moisture, (4) the composition of the 

 manure, and (5) the nature of preservatives added. 



The higher the temperature the more rapidly will manure de- 

 cay. In aerobic fermentation of manure the temperature may rise 

 to 122 to 140, or even 158 F. On the other hand, in the interior 

 of the heap, where anaerobic fermentation is in progress, the tem- 

 perature rarely rises above 95 F. Experiments have indicated that 

 131 F. is the most favorable temperature for manure fermenta- 

 tions. 



As already explained, the supply of air determines whether 

 the slow-acting anaerobic ferment or the more vigorous aerobic fer- 

 ment predominates. The careful regulation of the two kinds of fer- 



