228 FARMYARD MANURE [chap. 



dryness and richness which causes the gardener to 

 describe horse manure as " hotter " than that produced 

 by cattle and pigs. Bacterial changes take place in it 

 more rapidly, and both a greater amount of ammonia 

 and a greater rise of temperature are produced by the 

 fermentation. The composition of the resulting farm- 

 yard manure also varies, to a certain extent, with the 

 litter employed. Straw is, of course, most general, and 

 though there are differences in composition between 

 wheat, oat, and barley straw, these differences are not 

 great, and are indeed less than the variation in the 

 composition of any one of them in different seasons. 

 Speaking generally, the straw is richer in cool seasons 

 and in more northern climates. The only other sub- 

 stance at all widely used for litter is peat moss ; it is 

 both somewhat richer in itself in nitrogen than is straw, 

 and possesses a greater absorbing capacity for the 

 liquid portions of the manure. It is doubtful, however, 

 whether the extra nitrogen in the peat moss is of much 

 service to the plant, nor do the bacterial changes in 

 making the manure go on so readily as with straw. 



The changes we shall now discuss refer to ordinary 

 farmyard manure made with straw, and these changes 

 may be divided into two groups — those taking place in 

 the carbon and the nitrogen compounds respectively. 

 So far as the carbon compounds — the fibre and other 

 carbohydrates in straw — are concerned, the chief change 

 that takes place is the anaerobic fermentation which we 

 have discussed when dealing with soils. A number of 

 organisms are present in the air and in dust, which at 

 once attack the carbohydrate material of the straw and 

 begin to burn it up, with the production of carbon 

 dioxide. The organisms, however, soon use up all the 

 oxygen that is contained in the air entangled in the 

 manure, whereupon the work is taken up by the 



