You should always begin by contacting the competent lower-level soil conservation authorities, which can usually be found at the Umweltverwaltung office of your Landkreis or kreisfreie Stadt. These offices are best equipped to handle such matters, as they are familiar with the relevant conditions and particularities. If you are unable to obtain the help you need from these sources, contact the relevant Landesumweltämter für Umwelt or Landesanstalten für Umwelt.