1. ETHZ, Institute of Plant, Animal and Agroecosystem Sciences (IPAS); Universitätsstrasse 2 CH-8092 Zurich Switzerland
2. Research Institute of Organic Agriculture; Ackerstrasse CH-5070 Frick Switzerland
3. Fenaco AG; Erlachstrasse 5 CH-3001 Bern
4. Dep. of Agronomy; Iowa State Univ.; Ames IA 50011