ABSTRACT

Humus is a natural product of the soil environment which is formed during the biological degradation of plant residues. Although the humus generally constitutes less than 1 to about 10% of the soil mass, it is a very important fraction. Simple phenolic substances in soil can be derived from degradation of plant phenolic polymers, such as lignin, and through microbial synthesis. Use of specifically 14C-labeled phenols, lignins, fungal melanins, and model humic acid polymers makes it possible to determine which of the constituent carbons of polymers are utilized most readily by the soil organisms and which are relatively more important in soil humus formation. The lignins of corn stalks were labeled by injecting specifically 14C-labeled ferulic or p-coumaric acids as lignin precursors into the stalks of growing plants and extraction of the ground stalks after harvest with hot ethanol to remove low-molecular- weight, labeled compounds.