Hindawi Publishing Corporation International Journal of Agronomy Volume 2012, Article ID 163054, 13 pages doi:10.1155/2012/163054 Research Article Changes in Soluble-N in Forest and Pasture Soils after Repeated Applications of Tannins and Related Phenolic Compounds Jonathan J. Halvorson, 1 Javier M. Gonzalez, 1 and Ann E. Hagerman 2 1 USDA-ARS Appalachian Farming Systems Research Center, 1224 Airport Road, Beaver, WV 25813-9423, USA 2 Department of Chemistry and Biochemistry, Miami University, 160 Hughes Laboratories, 701 East High Street, Oxford, OH 45056, USA Correspondence should be addressed to Jonathan J. Halvorson, jonathan.halvorson@ars.usda.gov Received 15 September 2011; Accepted 7 December 2011 Academic Editor: Dexter B. Watts Copyright © 2012 Jonathan J. Halvorson et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tannins (produced by plants) can reduce the solubility of soil-N. However, comparisons of tannins to related non-tannins on different land uses are limited. We extracted soluble-N from forest and pasture soils (0–5cm) with repeated applications of water (Control) or solutions containing procyanidin from sorghum, catechin, tannic acid, β-1,2,3,4,6-penta-O-galloyl-D-glucose (PGG), gallic acid, or methyl gallate (10 mg g −1 soil). After eight treatments, samples were rinsed with cool water (23 ◦ C) and incubated in hot water (16 hrs, 80 ◦ C). After each step, the quantity of soluble-N and extraction efficiency compared to the Control was deter- mined. Tannins produced the greatest reductions of soluble-N with stronger effects on pasture soil. Little soluble-N was extracted with cool water but hot water released large amounts in patterns influenced by the previous treatments. The results of this study indicate hydrolyzable tannins like PGG reduce the solubility of labile soil-N more than condensed tannins like sorghum procya- nidin (SOR) and suggest tannin effects will vary with land management. Because they rapidly reduce solubility of soil-N and can also affect soil microorganisms, tannins may have a role in managing nitrogen availability and retention in agricultural soils. 1. Introduction Tannins are reactive secondary metabolites produced by plants that affect important biological, chemical, and phys- ical processes in soil and couple primary productivity to biogeochemical cycles [1–4]. Tannin effects on decomposi- tion and nitrogen availability in soil have been a subject of research for more than fifty years [5, 6]. However, devel- opment of strategies for use of tannins as soil management tools has lagged, in part because few studies have specifically related them to improving plant productivity or soil fertility. Early tannin research was conducted on temperate agricul- tural soils [7–9], while recent work has concentrated more on their role in forest ecosystems [10–12] and tropical soils [13– 15]. These studies, however, have tended to emphasize the impacts of tannins on microbially mediated processes rather than on the more immediate abiotic interactions between tannins and soil and have made little attempt to frame their findings into the context of landscape effects. Tannins are believed to affect the nitrogen cycle through several direct and indirect mechanisms that reduce rates of net mineralization or nitrification. Some tannins are directly toxic to plants or microorganisms [16, 17] but their effects vary with particular tannin chemistry or among taxonomic groups [18]. Some tannins or related phenolic compounds are used by soil microorganisms as substrates increasing microbial demand for nitrogen and immobilization in microbial biomass [2, 12, 19]. Tannins can also reduce rates of mineralization or decomposition by affecting the activity of enzymes [20, 21] or by forming complexes with other proteins or organic nitrogen compounds via reversible non- covalent processes such as hydrogen bonding and hydropho- bic interactions (cf. [2, 22, 23]). The availability of the nit- rogen sequestered in tannin-protein complexes varies among species of plants, taxa of microorganisms, or even among strains of mycorrhizae [11, 24–28]. Tannins and related phe- nolics may also affect soil-N through interactions with inor- ganic soil fractions [3, 23, 29]. For example, tannin-related