512 NATURE AND PROPERTIES OF SOILS 



Table CIX 



COMPARATIVE YIELDS FROM YARD AND STALL MANURE. 



manure is very light in weight and has every appearance of 

 being burned. This condition, however, is produced by fungi 

 instead of bacteria, and the dry and dusty appearance of the 

 manure is due to the mycelium, which penetrates in all di- 

 rections and uses up the valuable constituents. Manure thus 

 affected is of little value either as a fertilizer or as a soil 

 amendment. 



290. Evaluation of farm manure. — For purposes of com- 

 parison, experimentation, and sale, farm manures are often 

 evaluated in a way similar to that used with commercial fer- 

 tilizers. The great difficulty here lies in arriving at prices 

 for the important constituents which are at all comparable 

 with the value of the manure in the field. If the value of the 

 ammonia in manure is arbitrarily placed at 15 cents a pound, 

 phosphoric acid at 5 cents, and potash at 8 cents, certain 

 tentative calculations may be made. While such assumptions 

 do not establish the commercial value either of fresh or 

 stored manure, they are of some use in comparisons and gen- 

 eralizations. The average manure, as it goes on the land, car- 

 ries about 12 pounds of ammonia, 5 pounds of phosphoric 

 acid, and 10 pounds of potash. Using the prices above, such 

 manure is worth commercially about $3.00 a ton. 



The commercial evaluation must be applied with care be- 

 cause of the many factors tending to vary the composition of 



