Phenolic Acids in Oats, Wheat, Sorghum, and Corn Residues and Their Phytotoxicity1

Abstract Five phenolic acids, ferulic, p‐coumaric, syringic, vanillic, and p‐hydroxybenzoic, were quantitatively estimated in corn, wheat, sorghum, and oats residues, p‐Coumaric acid was present in greater concentration than the other acids. Acid and base hydrolysis were used to free the acids from the bound form. Higher concentrations of phenolic acids were found in the alkaline hydrolysate, indicating that the acids are probably bound by an ester‐type linkage. Concentrations of the cinnamic acid derivatives in the acid hydrolysate are probably low due to the breakdown of the free phenolic acids after acid hydrolysis. It appears that under ideal decomposition conditions, p‐coumaric acid might be released in sufficient quantity in localized areas of the soil to affect plant growth.