380 SOILS: PROPERTIES AND MANAGEMENT 



Weight, Lime Content, and Acidity of Green Manures 

 to the Acre 



As decomposition proceeds the acids are oxidized, and 

 finally basic material is held largely in combination with 

 so-called humus of the soil. This is doubtless in the 

 form of a colloidal complex, not a definite chemical com- 

 pound. Analyses by Snyder 1 of purified humous ash 

 from eight productive prairie soils have been averaged 

 and are presented in tabular form in paragraph 97. 



The quantity of basic material ordinarily held by the 

 organic matter of the soil is small compared with the 

 total soil content. The bases contained in humus are 

 principally potassium and sodium — not calcium, as 

 might be expected in the salt of an organic acid formed 

 in the soil. Humus in the soil tends to overcome acidity 

 and functions as an alkali. In respect to its composition 

 and properties, much of it resembles a colloidal com- 

 plex rather than a chemical combination of soil bases 

 with organic acids. 



It has often been observed that land from which forest 

 has been cleared will yield good crops of red clover for 



1 Snyder, Harry. 

 41. 1895. 



Soils. Minnesota Agr. Exp. Sta., Bui. 



