i9o8.] 



Farmyard Manure. 



13 



farmyard manure are thus exceedingly complex ; it is in the 

 early stages that the bacterial actions are most rapid, and they 

 fall chiefly upon the soluble nitrogenous compounds like urea. 

 At this time the greatest losses of nitrogen take place, both by 

 volatilisation of ammonia and evolution of nitrogen gas, and 

 so active is the oxidation that the temperature of the mass 

 rises continually. If the rate of oxidation be promoted 

 by occasionally turning over the mass, as in preparing a hot 

 bed or a mushroom heap, the rise in temperature is much in- 

 creased, at the same time the losses of nitrogen rise rapidly 

 and the amides and ammonium carbonate disappear more 

 quickly. What the gardener calls " taking the fire " out of the 

 manure means so reducing the free ammonia that the material 

 is no longer injurious to a plant's roots, though it still remains 

 rich in nitrogen and organic matter capable of further decay. 

 As soon as the first violent reactions are over, especially as the 

 mass becomes consolidated by trampling and the oxygen in the 

 entangled air used up, the rate of change slows down consider- 

 ably ; it now consists mainly in the attack of the anaerobic 

 organisms upon the carbohydrate material. The long strawy 

 dung begins to change to " short " or rotten manure, and this 

 change may continue slowly for years, until all trace of structure 

 is entirely gone and only a brown pulp is left. During this 

 second change but little loss is experienced by the nitrogenous 

 compounds if the mass be kept tightly pressed and moist so 

 as to exclude air ; there will be no loss of fertilising constituents, 

 only a gradual decline of weight as some of the carbon com- 

 pounds are converted into gases. Of course, as the manure 

 gets older and shorter it becomes richer in nitrogen ; this 

 apparent increase is, however, simply due to the loss of non- 

 nitrogenous carbon compounds, so that the nitrogen, which 

 does not waste, always bulks larger and larger in the residue. 

 But though there is no loss in nitrogen in these later stages the 

 more active compounds, such as ammonia and the easily 

 decomposable amides, become converted by bacterial action 

 into compounds which take longer to reach the plant when 

 the manure finally gets in the soil. 



One other change sometimes takes place when the manure is 

 allowed to get too loose and dry ; instead of bacteria, fungi 

 begin to develop very rapidly and the whole mass becomes 



