An agricultural implement, comprising: a trench opening assembly; a trench closing assembly; a trench depth sensor comprising a first part and a second part, said first part comprising at least one elongate member, the first part being disposed on the implement such that, in use, said at least one elongate member is disposed in a trench in a soil surface opened by said trench opening assembly, said second part operably connected to the agricultural implement and disposed to measure a distance to said elongate member, wherein the second part is disposed over said elongate member; characterized in that: said second part is disposed on said trench closing assembly and one of: 1) the second part comprises a radar and is disposed to measure a distance to said soil surface and to said elongate member; 2) the second part comprises a Hall effect sensor and is disposed to measure a distance to said elongate member, and one of i) said elongate member generates a magnetic field as current flows through said elongate member, or ii) a magnet is disposed on said elongate member; 3) the second part comprises an electromagnetic induction coil and is disposed to measure a distance to said elongate member; or 4) the agricultural implement further comprising a radio signal generator and a phase detector, said elongate member being one of a transmitting antenna and a receiving antenna, and said second part comprising an antenna that is one of a receiving antenna when said elongate member is a transmitting antenna and a transmitting antenna when said elongate member is a receiving antenna part. a trench opening assembly; a trench closing assembly; a trench depth sensor comprising a first part and a second part, said first part comprising at least one elongate member, the first part being disposed on the implement such that, in use, said at least one elongate member is disposed in a trench in a soil surface opened by said trench opening assembly, said second part operably connected to the agricultural implement and disposed to measure a distance to said elongate member, wherein the second part is disposed over said elongate member; characterized in that: said second part is disposed on said trench closing assembly and one of: 1) the second part comprises a radar and is disposed to measure a distance to said soil surface and to said elongate member; 2) the second part comprises a Hall effect sensor and is disposed to measure a distance to said elongate member, and one of i) said elongate member generates a magnetic field as current flows through said elongate member, or ii) a magnet is disposed on said elongate member; 3) the second part comprises an electromagnetic induction coil and is disposed to measure a distance to said elongate member; or 4) the agricultural implement further comprising a radio signal generator and a phase detector, said elongate member being one of a transmitting antenna and a receiving antenna, and said second part comprising an antenna that is one of a receiving antenna when said elongate member is a transmitting antenna and a transmitting antenna when said elongate member is a receiving antenna part. 1) the second part comprises a radar and is disposed to measure a distance to said soil surface and to said elongate member; 2) the second part comprises a Hall effect sensor and is disposed to measure a distance to said elongate member, and one of i) said elongate member generates a magnetic field as current flows through said elongate member, or ii) a magnet is disposed on said elongate member; 3) the second part comprises an electromagnetic induction coil and is disposed to measure a distance to said elongate member; or 4) the agricultural implement further comprising a radio signal generator and a phase detector, said elongate member being one of a transmitting antenna and a receiving antenna, and said second part comprising an antenna that is one of a receiving antenna when said elongate member is a transmitting antenna and a transmitting antenna when said elongate member is a receiving antenna part.