Canopy Drip: A Source of Mobile Soil Organic Matter for Mobilization of Iron and Aluminum

Abstract

Abstract Leaf leachates, simulating canopy drip during rainfall, were collected from southern red oak ( Quercus falcata var. pagodaefoliz Ell. ), live oak ( Quercus virginiana Mill. ), and longleaf pine ( Pinus palustris Mill. ), which were the principal tree species growing on soils with spodic horizons on the North Carolina Coastal Plain near Ft. Caswell. The samples of canopy drip were immediately chilled, filtered, and freeze‐dried. From the representative canopy drip sampled it was estimated that approximately 20 kg/ha per year of organic matter could be contributed to the soil from this source. In the laboratory, 139 to 1,480µ moles of Fe or 460 to 1,450µ moles of Al/g of freeze‐dried canopy drip were complexed from nitrate salt solutions depending on the concentration of the leachate solution. This amounts to a possible field mobilization of 0.15–1.53 and 0.22–0.70 kg/ha per year of Fe or Al, respectively. The active components responsible for Fe and Al mobilization were determined to be polyphenols, reducing sugars, and organic acids. Paper chromatograms and reducing‐sugar analyses indicated that the polyphenol and reducing‐sugar contributions to soil as canopy drip were approximately 1 kg and 4kg/ha per year, respectively. Organic acids were not quantitatively determined. Thus, canopy drip was shown to be an important source of mobile soil organic matter for podzolization and other pedogenic processes.