Tandem Disk Harrow
Overview: The cutting and mixing action of a disk harrow varies with the diameter, weight and concavity of its blades; blade spacing; the angle of the disk harrow gang relative to the direction of travel; and operating speed. In dryland farming, the disk harrow can help prepare overwintered stubble or fallowed land for seeding.
In a mulch-till system that includes soil-structure improvement as part of its weed management, a tandem disk with 22" diameter blades on 9" spacing could create a fall seedbed for a winter cover crop by partially incorporating corn stubble; knock down the cover crop in spring; create a rough seedbed of overwintered residue for residue-managing planters; or run shallowly just before planting to kill all surface weeds. Larger diameter blades, or blades that are spaced farther apart, run at a higher speed, or set at angles of more than 18 percent are more aggressive.
Design Features: Tandem disks gangs are configured like a bowtie: the front gangs, left and right, lead with the outside ends ahead and angle back toward the center; the back gangs, in the mirror position, have the inner ends leading in the center of the tool and outside ends angling back. Gang angle is fixed at 18 or 20 degrees, or adjustable at lesser angles.
Offset disk harrow frames have two straight gangs, one behind the other, on a strong central H-frame. The gangs angle in opposite directions. Gang angle is adjustable, usually in the range of 25 to 48 percent. Offset disks, outfitted with heavier blades up to 28" diameter, are used more often for primary tillage and high residue.
Model for comparison: 21' tandem pull/drawn type
Rec. PTO HP: 120 to 170
Speed: 4 to 8 mph
List price: $22,500 to $24,200
Width range (all makers/all models): 6' to 23' for offset; 6' to 33' for tandem
Sources: 18, 21, 46, 76, 77, 85
Farmers: Bennett, de Wilde, Erisman, Gemme, Harlow, Kenagy, McKaskle, Spray, Muller