HARROWS

There are several types of harrows in use.  They may be classified according to the style of their teeth or cutting parts; they are as follows: 

Rolling cutter harrows.

Spring-toothed harrows.

Spike-toothed harrows.

Coulter-toothed harrows.

Chain harrows.

Brush harrows.

Plank or drag harrows.

These types vary in the depth to which they cut, and the degree to which they pulverize the soil.

Rolling cutter harrows. Harrows of this type (see Fig. 54) consist of one or more revolving shafts on which are arranged a number of concave disks.  These disks are either entire, notched, or made of several pieces fastened together.  Examples of these are the disk, cutaway and spading harrows.  These harrows cut and move the soil deeper than the other types.  They are especially adapted to work on heavy clay soils.

The value of this type of harrow as moisture preservers depends on the manner in which they are used.  If the disks are so set that they cover but a portion of the surface with a mulch of fine earth they leave a ridge exposed to the action of the wind and sun and the rate of evaporation is greatly increased.  The disks should be set at such an angle that the whole surface shall be stirred or covered.  Soils which need the disk harrow should generally be gone over again with some shallower working tool to smooth the surface.  An objection to the rolling cutters is that unless great care is taken they will leave the land in ridges and valleys.

The two gangs of disks throw the earth in opposite directions.  They are generally set to throw it from the centre and the result is a shallow double furrow the width of the machine.  By lapping each time the furrow is partially filled, but to get the land smooth a smoothing harrow should be used after the rolling cutter.

Spring-toothed harrows (Fig. 55).  Spring-toothed harrows with their curved spring teeth enter the soil readily, draw moderately easy and pass over obstructions without much difficulty.  They are very useful in new land that is full of roots and stumps and also stony land.  They pulverize the soil to an average depth.  They leave the soil in ridges.  The ridges can be leveled by a smoother in the shape of a piece of plank attached to the rear of the harrow.  On newly plowed grass land they tend to tear up the sod and leave it on the surface.  They also tend to drag out coarse manures when plowed in.

The original and more common form of the spring-toothed harrow is a floating harrow when at work.  That is, it rests on the points of the teeth and is dragged or floated over the ground.  A newer form of spring-toothed harrow, sometimes called the fallow cultivator, is mounted on high wheels and its action is largely controlled by them.  This form of harrow is claimed to do much better work than the floating harrow and may in a large measure displace the rolling cutter.  The weight of this harrow is entirely taken from the soil except in the wheel tracks, and the entire action is that of pulverizing and lightening the soil.