From:
Unasylva - Vol. 10, No. 3 - Control of brush and undesirable trees: II

Pipe Harrow--Interesting attachment for rocky ground-x5380e0l.jpg
FIGURE 26. Pipe harrow. This is a self-clearing harrow which has been found useful for clearing sagebrush and covering grass seed on ranges that are so rocky and rough that other implements cannot be used. Plans for - its construction can be obtained from the U.S. Forest Service, Washington 25, D.C. (Oregon Extension Service)


Pipe harrow (Figure 26). The pipe harrow or Dixie drag was built for the removal of mature sagebrush on very rocky land. It consists of a series of pipes beset with steel spikes, dragged behind a horizontal spreader bar. Each pipe is swiveled so that it rotates freely and cleans itself of stems and clods. It bounces over the rocks, spins, rips out brush plants, gouges into the soil, and covers seed where enough soil is present. In the process it removes from 50 to 70 percent of the sagebrush. The rockier the ground - up to a point - the better it works and cleans itself.

The pipe harrow does not approach the various disc harrows in effectiveness, either as to kill of brush or to seedbed preparation. As stated, however, it is specifically designed for use on land too rocky for these latter implements to work without excessive breakage. The pipe harrow is a sturdy implement. Breakage is uncommon but the spike teeth and the swivels wear out in time. A 14-foot (425 cm.) unit can be pulled by a 50-horsepower tractor. If two harrows are used side by side, they can be pulled with an 80-horsepower tractor, although a heavier one is more efficient. On side slopes, the harrow should be equipped with troughs to keep them from jumping across one another.


From:
http://reveg-catalog.tamu.edu/07-Site%20Preparation.htm

Pipe Harrow--Interesting attachment for rocky ground-pipeharrow.jpg

Pipe harrows were designed to remove sagebrush and bitterbrush on rough terrain with rocks. One trip over removes a moderate amount of sagebrush and twice over removes a very high percentage. Pipes can be removed from the main beam to reduce brush removal and form special patterns. Users report 50 to 70 acres/day productivity. They are well suited to clearing sites in patterns to benefit wildlife. Seeding is conducted during single-pass harrowing and during the final pass of double-pass harrowing to establish desirable species. If sufficient desirable grasses are present, seeding may not be necessary.