1. Lantmännen, Grain Department, SE-531 87 Lidköping, Sweden.
2. Corresponding author. Phone: +46 510 88559. Fax: +46 510 88810. E-mail: thomas.s.borjesson@lantmannen.com
3. Precision Agriculture, Dept. of Soil Science, SLU, P.O. Box 234, SE-532 23Skara, Sweden.
4. Dept. of Microbiology, SLU, P.O. Box 7025, SE-750 07 Uppsala, Sweden.