114 SOILS AND FERTILIZERS 



rials either alone or jointly with lime. Ordinary prairie 

 soils, for the first ten years after breaking, are usually 

 well supplied. Swampy, peaty, and muck soils contain 

 large amounts ; in fact, they are often overstocked and 

 are improved by reducing the humus content. 'Alkali' 

 soils are usually deficient in humus. 



123. Active and Inactive Humus. When soil has 

 been long under cultivation, and no manures have been 

 used, the nitrogen and mineral matters combined with 

 the humus are reduced. The humus from long-culti- 

 vated fields contains a higher per cent of carbon than 

 from well-manured or new land; it is also less active 

 because of the carbon which does not readily undergo 

 oxidation. 9 



124. Influence of Different Methods of Farming upon 

 Humus. The system of farming has a direct effect 

 upon the humus content and the composition of the 



