COPPER FRACTIONS EXTRACTED BY MEHLICH-3 FROM SOILS AMENDED WITH EITHER CUSO4 OR COPPER RICH PIG MANURE

The Mehlich-3 procedure is being adapted as a general soil test becaus e it has the advantage of simultaneous extraction of P, macronutrient and micronutrient cations, as well as an improved ability to extract C u over that of the double acid soil test. It would be desirable if thi s procedure could be used to estimate both deficient and toxic Cu leve ls in soils. This study was undertaken to determine soil Cu extraction patterns of Mehlich-3. Soils used were a Bertie fine sandy loam (fine -loamy, mixed, thermic Aquic Hapludult), Guernsey silt loam (fine, mix ed, mesic, Aquic Hapludalf), and a Starr-Dyke clay loam (fine-loamy, m ixed, thermic Fluventic Dystochrept-clayey, mixed, mesic Typic Rhodudu lt) from the Atlantic Coastal Plain, Appalachian, and Piedmont regions of Virginia, respectively. Copper was applied to field plots at an av erage 13-year cumulative level of 365 kg ha-1 as either Cu rich pig ma nure or CuSO4. Although Cu application exceeded the USEPA maximum safe Cu loading rate of 280 kg ha-1 for these soils, the pig manure and Cu SO4 treatments had no affect on corn grain yield or Cu concentration, however, there was a trend toward reduced early season growth on one o f the three soils (i.e., on the Bertie soil). Applied Cu was held by t he three soils in largely unavailable forms. Soils were obtained for l aboratory experiments from the control and treatments that received ei ther Cu rich manure or CuSO4 with Cu levels equivalent to that in the manure. Soil samples were divided into two groups; one was pre-extract ed by the Mehlich-3 procedure and the other was not pre-extracted. Sam ples were then sequentially extracted to determine exchangeable, speci fically adsorbed, organically bound, and oxide occluded Cu fractions r emaining in the soil. The amount of Mehlich-3 extractable Cu was a fun ction of total applied Cu, and the amount Mehlich-3 extracted from the manure treatment was greater than or equal to that extracted from the CuSO4 treatment. The Mehlich-3 procedure extracted mainly the exchang eable and specifically absorbed Cu at both relatively high and low lev els of Cu in the three soils. Because these are the available Cu fract ions, the procedure will likely be suitable to estimate both deficient and toxic Cu levels.