An improved coulter assembly (10) includes a rotatable coulter blade (12) and a supporting assembly (14) having a parallel linkage arm assembly (34) and an active piston and cylinder assembly (58). The assembly (14) serves to maintain the blade (12) at a depth of at least about four inches, in order to prevent clogging of the assembly (10) during use. Another coulter assembly (110) includes a knife adjustment assembly (122) allowing selective vertical and angular adjustment of the knife (116) relative to the coulter blade (112).
