Plant Phenolic Acids in Soils: A Comparison of Extraction Procedures

Abstract

AbstractPlant phenolic acids have been found in plants and soils and some evidence suggests their involvement in biochemical interactions between plants (allelopathy) and organisms living in the soil. This study was conducted to compare the more common extraction procedures used in the recovery of water‐soluble phenolic acids from soil. Various extraction procedures were employed in the recovery of ferulic acid (4‐hydroxy‐3‐methoxycinnamic acid) from steam sterilized soil materials sampled from the A1 and B1 horizons of a Cecil soil (Typic Hapludults, clayey, kaolinitic, thermic) and a Portsmouth soil (Typic Umbraquualts, fine loamy, mixed, thermic). Ferulic acid was added (1000 mg/kg) to soil materials, allowed to equilibrate for 90 d, extracted and quantified by high‐performance liquid chromatography. Eight extracting solutions [H2O, methyl alcohol (CH3OH), 0.5 M sodium acetate (CH3CHOONa), 0.05 and 0.5 M diethylenetriaminepentaacetic acid (DTPA), 0.05 and 0.5 M ethylenediaminetetraacetic acid (EDTA), and 2 M NaOH] and various extraction times were used to recover ferulic acid from soil materials. Amounts of ferulic acid recovered from the A1 horizons were significantly lower than the amounts recovered from the B1 horizons for both Cecil and Portsmouth soil materials. Water and CH3OH recovered the least amounts of ferulic acid, whereas NaOH and 0.5 M DTPA recovered the most. In the B1 horizon materials, a major portion of the ferulic acid anions appeared to be absorbed by polyvalent cations (either exchangeable or nonexchangeable). This paper emphasizes the necessity of choosing the appropriate phenolic acid extractant for the soil phenolic acid fraction of interest.