Humus soil precursors

The process by which humus is formed is called humification. Soil humus is similar to its lignin precursors, but has more carbojg lic acid groups. Part of each molecule of humic substance is nonpolar and hydrophobic, and part is polar and hydrophilic. Such molecules are called amphiphiles, and they form micelles (see Section 5.4 and Figure 5.4), in which the nonpolar parts compose the inside of small colloidal particles and the polar functional groups are on the outside. Amphiphilic humic substances probably also form bilayer surface coatings on mineral grains in soil. 

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