CHARACTERIZATION OF COPPER AVAILABILITY AND CORN SEEDLING GROWTH BY A DTPA SOIL TEST

A greenhouse experiment was conducted to determine (i) the physical and/or chemical properties of soils which control Cu availability; (ii) if 0.0004M DTPA (diethylenetriaminepentaacetic acid) effects a small exchange of Cu in soils; and (iii) if pCu, estimated by iterative computer calculations based on DTPA stability constants, reflects the availability of Cu in soils. The growth and Cu accumulation of corn seedlings were studied using 16 northeastern United States soils, each treated to contain 125, 250, and 500 ppm total Cu. Soil pH, percent organic matter, cation exchange capacity (CEC), percent clay, percent silt, percent sand, percent Na2O, and DTPA-extractable Cu were measured in order to relate soil properties to Cu availability and seedling growth. The soil factors affecting the mean soil Cu activity coefficient and therefore controlling Cu availability were pH and the silt fractions of Na-bearing minerals. The DTPA at 0.0004M with a 1:10 soil-to-solution ratio did not effect a small exchange for Cu. For most soils, the DTPA extracted the labile Cu. Finally, when medium and fine-textured soils are tested by the Baker DTPA soil test, resulting pCu values of approximately 11.9 and less should in general indicate high soil Cu availability (i.e., soil Cu availability 0.16 ppm) and reduced corn growth. © 1982 Soil Science Society of America.