HR: 1340h
AN: B23D-1599 [Abstracts]
TI: Tannin-Metal Interactions in Soils: An Incubation-Extraction Approach in Hill-Land Environments
AU: * Gonzalez, J M
EM: javier.gonzalez@ars.usda.gov
AF: USDA-ARS-AFSRC, 1224 Airport Rd., Beaver, WV 25813-9423, United States
AU: Halvorson, J J
EM: jonathan.halvorson@ars.usda.gov
AF: USDA-ARS-AFSRC, 1224 Airport Rd., Beaver, WV 25813-9423, United States
AB:
Tannins, plant polyphenols known to react with proteins, metals and soil organic matter, are commonly found in
the vegetation growing in Appalachian hill-lands. Establishing silvopastoral grazing systems in these
environments is a means for improving productivity however the fate of tannins in soils and, in particular, the effect
on solubility/mobility of metals in soils is poorly understood. Soils from forest and pasture systems were
sampled from two depths, treated with tannic acid or related phenolic compounds, and analyzed for metals in
solution. The amount of Mn and Ca detected in solution varied among the different phenolic treatments, highest
for gallic acid, and was also influenced by depth and land use. As expected, the Ca content in solution was
correlated with the electrical conductivity (EC) and the Mn content was correlated with the redox potential in
solution. Interestingly, the EC was also correlated with both Mn content and redox potential. The higher Ca content
found in solution may result from the low pH of the phenolic compounds. The higher Mn in solution may result
from the redox reaction of Mn (IV) oxides with the phenolic compounds, producing soluble Mn2+ and quinones.
These quinones are very reactive compounds that can self-polymerize and/or copolymerize with other
biomolecules, such as amino-containing compounds and carbohydrates, to form humic-like substances.
Successful management of silvopastures, requires an understanding of factors that affect the quality and quantity
of plant secondary compounds like tannins entering soil not only to increase forage productivity but also to
enhance formation/stabilization of soil organic matter to increase nutrient cycling and reduce the toxicity risk of
some metals such as Mn.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0461 Metals
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting