Bacteria in Manures. 211 



nished food for bacteria, especially the nitrogen-fixing 

 ones, and have added to the humus content of the soil. 

 J t is now realized that the value of manure is not deter- 

 mined alone by the amount of potassium, phosphorus, 

 and nitrogen it contains, but the organic matter itself 

 exerts a most important effect. Market gardeners find 

 it advantageous to pay more for manure than the fertiliz- 

 ing ingredients alone would cost in the form of commer- 

 cial fertilizers. For most soils the greater the amount of 

 organic matter that can be returned the better for the 

 soil. The practice of hauling manure directly to the field 

 from the stable is probably the most successful means of 

 conserving its value. 



If very large amounts of manure are to be applied, as 

 in market gardening, unrotted manure cannot be used on 

 account of its injurious effect on the crop. The amounts 

 usually applied in farm practice have no injurious effect. 



The potassium and phosphorus of the manure are 

 changed to soluble form in the decomposition processes. 

 These can be lost from the manure only through the 

 leaching of the pile. The largest loss is liable to occur in 

 the case of nitrogen when ammonia is freely formed. In 

 order to prevent the loss in the latter form, materials 

 such as gypsum, kainit, sulphuric acid, and peat, that 

 were supposed to fix the ammonia, were formerly em- 

 ployed. It is now recognized that the loss prevented by 

 their use is very small, and they are no longer used to 

 any extent. 



Hot and cold manures. Horse and sheep manures 

 are called hot manures because if placed in a pile they 

 heat or fire fang. Cow and hog manure are cold ma- 

 nrires. During their decomposition enough heat is 

 evolved to keep them from freezing in quite severe 



