Irreversibly sorbed phenolic acids

In conclusion, the water-autoclave extraction procedure when compared to the EDTA extraction procedure underestimated the total available ferulic acid in the soil by roughly 5% for Cecil A and 22% for Cecil B. In addition to the quantitative difference there also appeared to be a difference in the types of the sorbed ferulic acid recovered. The water-autoclave-procedure recovered some irreversibly sorbed phenolic acids from Cecil A soil since only 55% of the sorbed phenolic acid recovered was utilized by microbes. This difference should not be surprising since the physical and chemical processes of the two extraction procedures, i.e., chelation vs. 

Since the water content and solutions added to soil samples was determined and known, respectively, free , reversibly sorbed, and available phenolic acids of a soil sample could be expressed in either p,M or p,mol/g soil. In addition since under laboratory conditions the concentrations of phenohc acids added to sterile soils were known, the amount (% or p,mol/g soU) of irreversibly sorbed phenohc acids (e.g., bound into recalcitrant organic matter or onto clay minerals) could also be estimated. 

When phenolic acids enter the soil environment they are reversibly and irreversibly sorbed to soil particles, polymerized, oxidized, reduced, leached, utilized by microbes, and taken up by roots. Rates for these various processes are highly variable and depend on soil type, biotic and physicochemical soil environmenL types and mixtures of phenohc acids in or added to soils, and time, among others. To eliminate the effects of soil microbes, soils may be autoclaved. Concentrations of individual available phenolic acids in soils at a given point in time may be estimated by extracting soils with appropriate extractants and HPLC analysis. Based on our soils, we recommend water for estimating soil solution concentrations and neutral EDTA for soil solution and reversibly sorbed phenolic acid concentrations. However, the effectiveness of neutral EDTA in recovering available phenolic acids in all other soils should not be assumed. Reversibly sorbed phenolic acids increased or decreased as soil solution concentrations and multivalent cations increased or decreased, respectively. 

Recovery of phenolic acids by NaOH from amended soil samples was equal to or greater than those recovered from non-amended soil samples. The difference (minus approximately 0.01 p,mol/g soil) in recovery between amended and non-amended phenolic acid soils represented a portion of the amended phenolic acids (i.e., 1 M NaOH extractable) that had been irreversibly sorbed during the equilibration and/or incubation periods. Values for 1 M NaOH extractable phenolic acids from non-amended soils were < 0.0017 xmol/g soil for Cecil B (0.2% organic matter) soil samples and ranged from 0.013 xmol/g soil for ferulic acid to 0.073 p,mol/g soil for p-coumaric acid in the Cecil A (3.7% organic matter) soil samples. Differences between amended and non-amended soils ranged from 0 xmol/g soil for p-coumaric acid to 0.024 p,mol/g soil for ferulic acid in Cecil A soil samples and 0.013 p,mol/g... 

Rates of phenolic acid sorption (reversible and irreversibly sorbed or fixed) to sterile soils varied over time. Immediately after addition of phenolic acids to soils (first 1-4 h) there was a very rapid sorption (primarily irreversible sorption) for both the cinnamic acid and benzoic acid derivatives (Figs. 2.15 and 2.18 Blum et al. 

Phenolic acids in soils occur either in a free state in the soil solution, reversibly sorbed to soil particles, fixed (irreversibly sorbed) very tightly to soil particles (e.g., recalcitrant organic matter, and clays), and/or on and in living and dead plant tissues/residues ( free , reversibly sorbed, and fixed). Of general interest to plant-plant allelopathic interactions are the free and reversibly sorbed states frequently referred to as the available fraction. Of particular interest is the active fraction of available phenolic acids, the fraction of available phenolic acids that actually interact with seeds, roots and microbes. Unfortunately we presently do not have a means of quantifying the active fraction, thus the focus on the available fraction. 

Con 4 Phenolic acids were rapidly and irreversibly sorbed to soil particles and/or incorporated into the recalcitrant organic matter within the soil. 

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