Harrow, << HAR oh, >> is an implement that farmers use to break plowed earth into smaller pieces before they plant seeds. The clods of earth left by the plow are too large for the delicate shoots to break through and too rough for machines to travel over during cultivation and harvesting. The harrow is also used to kill weeds and cover newly sown seeds. There are three main types: (1) the disk harrow, (2) the spike-tooth harrow, and (3) the spring-tooth harrow.
The disk harrow is a set of sharp disks, from 16 to 28 inches (41 to 71 centimeters) in diameter, mounted on a shaft. Such a unit is called a gang. Disk harrows commonly have one or two pairs of gangs. Each pair ranges from 5 to 50 feet (1.5 to 15 meters) wide. As the harrow is pulled forward, the disks revolve and cut the soil. If the soil is not hard, a disk harrow can be used as both harrow and plow. Such harrows can be weighted to make the disks cut more deeply. Disk harrows require more pulling power than do other types of harrows. They did not come into wide use until farmers began using trac-tors instead of farm animals to pull them.
The spike-tooth harrow is a set of two to six steel frames. Each frame can work an area about 5 feet (1.5 meters) square and has rods running across it. Steel teeth on the rods “comb” the soil as the harrow is pulled. This harrow works best on well-cleared land.
The spring-tooth harrow consists of a steel frame that may be from 5 to 40 feet (1.5 to 12 meters) wide or wider. Steel teeth shaped in a half circle are bolted into the frame. With a springing action, the teeth tear into the soil when the harrow moves. These harrows are wellsuited for rough, rocky ground.
