Power Harrow

A power harrow is a secondary-tillage implement used after primary cultivation (such as ploughing or deep loosening) to refine the surface into a seedbed. Unlike a plough, it does not invert the soil; its rotating tines work horizontally to shatter clods and produce an even, level surface for sowing.

It is distinguished from a passive chain or spike harrow by being actively driven from the tractor PTO, which lets it develop a fine tilth even in firmer conditions and allows working depth and intensity to be set somewhat independently of forward speed.

1. The tractor PTO drives a gear train along the top of the implement
2. Paired tines mounted on rotors turn on vertical axes, sweeping through the topsoil
3. The rotating tines crumble clods and level the surface without turning it over
4. A following roller or crumbler bar consolidates the tilth and controls working depth
5. In combination units, a seed drill mounted behind sows into the freshly prepared seedbed

The power harrow sits at the seedbed-finishing stage of a conventional tillage sequence, after primary loosening has fractured and, where used, inverted the soil. Its ability to create a level, fine seedbed in one or two passes, and to be combined directly with a drill, can reduce the number of separate field operations and therefore the total field traffic before sowing.

Tilth fineness is governed by rotor speed, forward speed, working depth, and soil moisture, and an over-fine tilth can increase the risk of surface crusting and erosion on vulnerable soils. Matching working intensity to the crop and conditions — rather than working the soil as finely as possible — is generally preferred.