Nature and Classification of Soil Humic Substances

As introduced in Chapter 7, HS are usually classified into fractions in terms of solubility  

Fulvic acids (FAs) the fraction that is soluble in water at any pH value 

HS are not alone in soils but often appear associated with mineral colloids, small ions, and other organic compounds this point will be addressed in Chapter 14, but now we note that it implies a separation procedure to isolate HS for their study. 

FIGURE 10.1 Fractionation scheme of hmnie substances, based on the IHSS procedure. (From Swift R. S., Methods of Soil Analysis. Part 3. Chemical Methods, Soil Science Society of America Book Series 5, Madison, WI American Society of Agronomy-Soil Science Society of America, January 1,1996.) 

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