OM. 

 35 



30 



25 



20 



15 



10 



oc. 



21 



18 - 



15 ~ 



12 - 



9 - 



3- 



Organic Soil Materials 



.-$** 



^^ 



AM 



^ 



\&3 



Nonorganic Soil Materials 



10 



20 



30 



40 



50 



Percent clay 



Organic soil materials thai are never saturated lof more than a lew days and 

 containing more*than 20 percent organic carbon are also Included. 



Figure 1. Organic carbon requirements for organic soil materials. 



soil materials that are not thixotropic by the formula 

 n=(A-0.2R)/(L+3H), 



where A=% water in a soil at field condition, calculated on a dry weight basis; R=% silt plus 

 sand; L=% clay; and H=% organic matter (organic carbon X 1.724). Most soil materials deposited 

 under water and never dried below field capacity have n-values of 1 or more (Figure 1). The 

 n-value is helpful in indicating whether you can walk on the soil in the undrained state and the 

 degree of subsidence that would occur following drainage. 



Contact with brackish or saline water affects soil properties and plant communities that grow 

 on the soil. Chabreck (1972) reported a salinity classification related to the salt tolerances of 



62 



