SEMINAR GIVEN AT U.F. INDIAN RIVER RESEARCH & EDUCATION CENTER
Ft. Pierce, Florida
March 28, 2001
Mobility of Copper and Phosphate in Soils: Surface Adsorption, Colloids, and the Implications for Management Practices
Dr. William Fish
Environmental Sciences and Resources/Civil Engineering
Portland State University, Portland, Oregon 97207
Copper (Cu) and phosphorus (P) are of concern in managing the impact of citrus cultivation on surface water quality. Cu and P both tend to adsorb (bind) strongly to soils, although the strength and capacity of this binding depend on factors such as the grain-size distribution, organic carbon content, and iron oxide/hydroxide content of the soil. Cu and P are an especially interesting pair to examine together because the mechanism by which Cu attaches to soils is in one sense the
Aopposite@ of the way P attaches to soils. Consequently, high soil pH favors Cu binding whereas low soil pH favors P binding. Natural soil organic matter (humic material) further complicates this picture by introducing a complex, partially soluble or colloidal, anionic polyelectrolyte into the system. Humic materials may enhance the apparent mobility of both Cu and P. Finally, iron oxide/hydroxide minerals in the soil may also form stable colloidal suspensions in soil water, thereby potentially promoting the mobility of Cu, P and other soil constituents. Knowledge of these processes helps us understand the possible consequences of various types of tillage or irrigation practices with respect to minimizing the release of Cu and P to surface waters.Return to Bill Fish’s Home Page