138 SOILS: PROPERTIES AND MANAGEMENT 



the discussion of the composition of that great group oi 

 intermediate compounds, called humus, arising from the 

 decay of the organic matter of the soil. While Schreiner 

 found twenty soils, out of a group of sixty taken in eleven 

 States of this country, to contain dihydroxystearic acid, 

 this does not necessarily mean that this compound in 

 itself is a serious detrimental factor. It is very likely 

 that such compounds are merely products of improper 

 soil conditions, and are to be considered as concomitant 

 with depressed crop yields. When such conditions are 

 righted, the so-called toxic matter will disappear. Good 

 drainage, lime, tillage, a balanced food ration, promoted 

 aeration and oxidation, are so efficacious in this regard 

 that permanent soil toxicity need never be feared by the 

 farmer. 



94. End products of humus decay. — As the processes 

 of chemical and biological decay of the soil organic matter 

 proceed, the simple compounds already noted begin to 

 appear. This change is of course coordinate with a 

 certain amount of synthetic action, but compounds thus 

 built up must ultimately succumb to the agencies at 

 work and suffer a splitting-up and reduction to simple 

 bodies. Carbon dioxide is one of the most important of 

 these compounds, being always a product of bacterial 

 activity. Its importance has already been noted in the 

 discussion of weathering. Here it heightens the solvent 

 power of water and tends to increase the amount of plant- 

 food carried in the soil solution. Carbonation is a direct 

 result of its presence. Carbon dioxide may also tend to 

 flocculate colloidal matter in soils, and thus benefit the 

 physical conditions. With increased organic matter in 

 any soil, there greater bacterial action and an increase 

 in the carbon dioxide evolved may well be expected. In 



