ORGANIC COMPOUNDS OF SOILS 



99 



106. Soils in Need of Humus. — Sandv and sandv 

 loam soils that have been cultivated for a number of 

 years to corn, potatoes, and small grains, without the 

 use of stable manures or the proper rotation of crops, 

 are deficient in humus. Clay soils, as a rule, do not 

 stand in need of humus so much as loam or sandy 

 soils. The mechanical condition of heavv clavs is. 



Carbon 



"^sS^Qxi/gem 



H 



N 



dj/? 



Figf. 2o. Humus from old soil. 



I Fig. 21. Humus from new soil. 



however, improved by the addition of humus-forming 

 material. 'Alkali' soils are usually deficient in humus. 

 Its addition to loam or sandy soils is beneficial in pre- 

 venting the soil from drifting because humus binds 

 together the soil particles. There are but few soils, 

 under ordinary cultivation, to which it is not safe to 

 add humus-forming materials. Ordinary prairie soils, 

 for the first ten years after breaking, are usually well 



