1. Institute of Soil Science and Land Evaluation; Soil Biology Section (310b), University of Hohenheim; Emil-Wolff-Str. 27 D-70593 Stuttgart Germany
2. 2326 Geology, Department of Environmental Sciences; University of California; Riverside CA 92521
3. Dep. of Agronomy; Iowa State Univ.; 2403 Agronomy Hall Ames IA 50011