Plant phenolic acids in soils: Sorption of ferulic acid by soil and soil components sterilized by different techniques

Abstract

Ferulic acid (4-hydroxy-3-methoxycinnamic acid) is produced by plants and subsequently released into soils, and appears to be involved in biochemical interactions between plants (allelopathy) and other organisms living in the soil. Knowledge of the processes affecting the concentrations of such potential allelochemicals in soil is essential to understand their roles in the soil environment. There is some information on the long-term physicochemical interactions of exogeneously-applied ferulic acid (FA) with soil materials that have been sterilized by autoclaving. Our aim was to determine the effects that soil sterilization treatments (autoclaving. methyl bromide and gamma irradiation) have on the recovery of exogenously-applied FA from different soil materials and components. Sterilization of soil was used to isolate physicochemical effects from microbial effects on FA. Ferulic acid was added at a rate of 5.15 mmolkg −1 to sterilized Al and Bl horizon material of Cecil (Typic Hapludults, clayey, kaolinitic, thermic), Portsmouth (Typic Umbraquualts, fine loamy, mixed, thermic) and White Store (Vertic Hapludalfs, fine, mixed, thermic) soils and to Georgia kaolin, gibbsite, goethite and Histosol materials. Samples were extracted within 2 min. and on days 1, 2, 4 and 8, with Mehlich III extradant. Immediate extractions were also made for nonsterilized soil materials. Extractable concentrations of Mn 2+ from sterilized soils were higher than concentrations from nonsterilized soils. Recovery of ferulic acid from soil materials sterilized by autoclaving was generally greater than recoveries from soil materials sterilized by methyl bromide or γ-irradiation. Methyl bromide treatment of gibbsite and goethite increased the “sorption” of applied FA. Recoveries of FA from sterilized and nonsterilized A1 soil materials were significantly lower than recoveries from B1 materials, irrespective of soil sterilization treatment. Changes produced by soil sterilization processes that affect the extractability of FA are greatly dependent upon the soil type and the kind of sterilizing treatment employed.