FORAGE MANAGEMENT SYSTEMS FOR SMALL-SCALE RUMINANT PRODUCTION IN THE APPALACHIAN REGION
Title: Sorption of tannin and related phenolic compounds and effects on extraction of soluble-N in soil amended with several carbon sources
Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 21, 2012
Publication Date: February 27, 2012
Citation: Halvorson, J.J., Gollany, H.T., Kennedy, A.C., Hagerman, A.E., Gonzalez, J.M., Wuest, S.B. 2012. Sorption of tannin and related phenolic compounds and effects on extraction of soluble-N in soil amended with several carbon sources. Agriculture. 2:52-72.
Interpretive Summary: Tannins, produced by plants, are able to attach to soil and reduce losses of soluble-Nitrogen (soluble-N) and thus could be important for managing soil organic matter (SOM), nutrient cycling, and water quality. However, we know little about how different classes of tannins and related compounds interact with different kinds of SOM. To address these questions, soil was collected from plots that had received annual amendments of several carbon substances (C-source) for five years. Samples were treated with water (Control) or solutions containing tannins or related compounds. After application, the amount of compound that affixed to the soil was determined together with the amount of nitrogen lost from soil. Sorption was low for non-tannin compounds, less than 15%, and unaffected by C-source. Sorption was higher for tannins, as high as 63%, and affected by C-source, with greatest sorption in soil from plots amended with biosolids, manure, alfalfa and canola residue compared to those amended with sucrose, wheat residue, cellulose, or compost. Extraction of soluble-N from soil was reduced by 18-24% by some tannins and non-tannin compounds but little impacted by C-source. For some treatments, the amount of carbon remaining in soil after the experiment was close to expected values confirming tannins or related compounds were attached onto soil and not otherwise lost. However, total soil-C remaining in samples treated with acidic compounds was unexpectedly lower than predicted values. The ability for soil to hold plant nutrients increased in samples after treatment with one tannin, but decreased after treatment with a related compound, and was not impacted by C-source. The patterns of sorption, observed in this study show different classes of tannins, but not related compounds, readily affix to soil and can be influenced by the quality of SOM. Some of these compounds can reduce solubility of nitrogen from soil. This information contributes to an assessment of the impacts of tannins and other phenolic compounds on SOM formation, nutrient cycling, and toxicity risk of some metals.
Some tannins, phenolic substances produced by plants, sorb to soil and reduce the extraction of soluble-N and thus could influence soil organic matter (SOM) and nutrient cycling. However, we know little about how these compounds interact with organic amendments in soil. Surface soil (0-5cm) from plots, amended annually with various carbon substances(C-source), was treated with water (Control) or solutions containing tannins or related phenolic subunits. Treatments included a polymeric flavonoid-based proanthocyanidin (SOR), catechin (CAT), tannic acid (TA), beta-1,2,3,4,6-penta-O-galloyl-D-glucose, (PGG), gallic acid (GA), and methyl gallate, (MG). We determined soluble-C and N in supernatants after application and a subsequent incubation in hot water (16 hr, 80 oC), to uncover evidence for sorption or effects on extraction of soil-N. Sorption was low for non-tannin phenolics, less than 15%, for MG, GA, and CAT, and unaffected by C-source. Sorption of SOR, TA and PGG was higher, about 23%, 42% and 63%, and impacted by C-source, greatest in plots amended with biosolids and manure, lowest in those amended with grass, wood, compost, wheat residue, sucrose, cellulose, or unamended soil. Extraction of soluble-N was little affected by C-source or by CAT, SOR, or MG, but reduced 18-24% by PGG, TA and GA. Total soil-C remaining in control samples and the CAT, SOR and PGG treatments was comparable to predicted values but low in the MG, GA and TA treatments, associated with the acidity of the solution pH. Soil cation exchange capacity increased following treatment with PGG by 5.3%, but decreased by about 6.5% with GA, irrespective of amendment. This study indicates different kinds of tannins, but not related phenolics, readily affix to soil and are influenced by C-source. Some of these compounds can reduce solubility of soil-N. Tannins and other phenolic compounds appear to have a role in the management of soils.