1. Soil Department; Agronomic Institute of Paraná State (IAPAR); 86001-970 Londrina PR Brazil
2. Embrapa Soja; Caixa Postal 231 CEP 86001-970 Londrina PR Brazil
3. Ohio State University; School of Environment and Natural Resources; Columbus OH 43210 USA
4. Department of Plant and Soil Sciences; University of Kentucky; Lexington KY 40546 USA