?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.au=Schmidtke%2C+Knut&rft.aulast=Schmidtke&rft.aufirst=Knut&rft.date=2008&rft.title=How+to+optimise+symbiotic+nitrogen+fixation+in+organic+crop+rotations+&rft.genre=proceeding