38 FRESH AND ROTTEN MANURE. 



in a fresh one. The distinction must not be lost 

 sight of which exists between relative increase 

 increase in the percentage of valuable constituents 

 and absolute increase. The increase in the value 

 of the manure by the changes of the manurial ingre- 

 dients from the insoluble to the soluble condition may 

 be effected at the expense of a considerable amount 

 of absolute loss of these valuable ingredients. This is 

 a point which is probably too often left out of account 

 in discussing the relative merits of fresh and rotten 

 farmyard manure ; and it is important that it should 

 be clearly understood. In the words of the late Dr 

 Voelcker: " Direct experiments have shown that 100 

 cwt. of fresh farmyard manure are reduced to 80 cwt. 

 if allowed to lie till the straw is half rotten ; 100 cwt. 

 of fresh farmyard manure are reduced to 60 cwt. if 

 allowed to ferment till it becomes ' fat or cheesy ' ; 100 

 cwt. of fresh farmyard manure are reduced to 40-50 

 cwt. if completely decomposed. This loss not only 

 affects the water and other less valuable constituents 

 of farmyard manure, but also its most fertilising in- 

 gredients. Chemical analysis has shown that 100 cwt. 

 of common farmyard manure contain about 40 Ib. of 

 nitrogen, and that during fermentation in the first 

 period 5 Ib. of nitrogen are dissipated in the form of 

 volatile ammonia; in the second, 10 Ib. ; in the third, 

 20 Ib. Completely decomposed common manure has 

 thus lost about one-half of its most valuable constitu- 

 ent/' While, of course, a very great amount of absolute 



