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Title: Changes in Soluble-N in forest and pasture soils after repeated applications of tannins and related phenolic compounds

Author
item Halvorson, Jonathan
item Gonzalez, Javier
item HAGERMAN, ANN - MIAMI UNIVERSITY - OHIO

Submitted to: International Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2011
Publication Date: 3/13/2012
Citation: Halvorson, J.J., Gonzalez, J.M., Hagerman, A.E. 2012. Changes in Soluble-N in forest and pasture soils after repeated applications of tannins and related phenolic compounds. International Journal of Agronomy. DOI: 10.1155/2012/163054.2012.

Interpretive Summary: Tannins produced by plants, can rapidly reduce the solubility of soil nitrogen (N). However, studies comparing the effects of different tannins to related compounds on different land uses are sparse. We compared soluble-N extracted from Appalachian forest and pasture soils by eight applications of water (Control) or solutions containing tannins or related phenolic subunits. Soluble-N extractions were reduced by tannins and more efficient from pasture than forest soil. Extractions with cool water were negligible but hot water released large amounts of soluble-N from soil in patterns influenced by the previous treatments. By the end of the experiment, a tannin, purified from sorghum, reduced soluble-N from forest and pasture soil by 8 and 23%, but the greatest effects resulted from a tannin purified from tannic acid that reduced cumulative extractions from forest and pasture soil by 27 and 43%. Our results indicated tannins and related phenolic compounds vary in their ability to reduce losses of N from soil and that their efficacy was influenced by land use. Increasing or maintaining the flows of these compounds into agricultural soils may be one strategy for managing soil fertility in Appalachian silvopastures. This information is useful to producers and conservationists for controlling nitrogen losses to the environment.

Technical Abstract: Tannins, reactive polyphenolic secondary metabolites produced by plants, can rapidly reduce the solubility of labile soil nitrogen (N). However, studies comparing the effects of different tannins to related compounds on different land uses are sparse. We compared soluble-N extracted from Appalachian forest and pasture soils (0-5 cm depth) by eight applications of water (Control) or solutions containing tannins or related phenolic subunits. Treatments included a polymeric flavonoid-based proanthocyanidin (SOR), catechin (CAT), tannic acid (TA), ß-1,2,3,4,6-penta-O-galloyl-D-glucose (PGG), gallic acid (GA), and methyl gallate (MG). After eight treatments, samples were rinsed with cool water (23 oC) followed by an incubation in hot water (16 hrs, 80 oC). After each step, the quantity of soluble-N extracted and the relative extraction efficiency compared to the Control (deltaSol-N) were determined. Key patterns of soluble-N, established with the first treatment, persisted throughout the experiment. Extractions were significantly reduced by the TA and PGG treatments and higher from pasture than forest soil. Extractions with cool water were negligible but hot water released large amounts of soluble-N from soil in patterns influenced by the previous phenolic treatments. Throughout the experiment, deltaSol-N varied as a Treatment x Use interaction showing tannins produced the greatest reductions of soluble-N with stronger effects on pasture soil. Although the first treatment with MG increased deltaSol-N, final cumulative extractions of soluble-N from forest or pasture soil were indistinguishable from the Control. The GA treatment did not affect forest soil but reduced soluble-N from pasture soil by 25% or nearly 100 mg kg-1. Treatment with CAT reduced extractions from both forest and pasture soil by 11% or about 27 and 47 mg kg-1. The condensed tannin, SOR, reduced soluble-N from forest and pasture soil by 8 and 23% or by 21 and 93 mg kg-1. Tannic acid, reduced soluble-N from forest soil by 22% or 58 mg kg-1 but from pasture soil by 40%, 156 mg kg-1. The hydrolyzable tannin, PGG, reduced cumulative extractions from forest and pasture soil by 71 and 176 mg kg-1 or by 27 and 43%. Our results indicated tannins and related phenolic compounds vary in their ability to affect the solubility organic soil-N and that their efficacy was influenced by land use. Increasing or maintaining the flows of phenolic secondary compounds into agricultural soils may be one strategy for managing nitrogen availability.