PRESERVATION OF FORAGE 37 



Conditions which cause spontaneous combustion are 

 not sufficiently well known to warrant any definite state- 

 ment as to just when hay is sufficiently cured to be safe. 

 There is apparently always risk unless the hay is thor- 

 oughly cured. 



The problem has been specifically studied by Hoffmann, 

 in Germany, who experimented especially with red clover 

 hay. He finds that the heat is generated through a 

 process of fermentation, probably enzymatic, in which 

 oxygen is taken from the air and the organic matter is 

 transformed into carbon dioxide and water. From this 

 additional moisture a secondary fermentation due to 

 bacteria takes place. If the hay has external moisture 

 when first stored, the fermentation is more rapid. The 

 preliminary fermentation causes a temperature of 56 C. 

 This temperature causes a second and more violent oxi- 

 dation to take place and the temperature rises to about 

 90 C. In further fermentation processes the heat slowly 

 rises to as high as 130 C., at which temperatures the hay 

 is charred. From theoretical consideration Hoffmann 

 figures that the temperature may rise to 190 C. In the 

 presence of oxygen ignition will take place at 150 C. or 

 higher. If, however, oxygen be excluded, ignition will not 

 occur, but the hay will be converted into a mass of charcoal. 



29. Statistics of hay yields. Yields of forage crops 

 per acre are much less accurately known than those of 

 grain crops. Reliable data of hay yields are available 

 mainly in connection with definite experiments. Esti- 

 mates of farmers upon which statistical and census 

 data are based are probably too large. It is a difficult 

 matter to estimate closely a yield of hay, and there is 

 little chance to become proficient, as hay yields are so 

 seldom weighed. On the other hand, the farmer sells his 



