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A disc harrow is a farm implement that is used to cultivate the soil where crops are to be planted. It is also used to chop up unwanted weeds or crop remainders. It consists of many Carbon steel and sometimes the Longer lasting Boron discs which have many varying concavity's and disc blade sizes and spacing, the later being a function of the final result required in a given soil type, and are arranged into two Sections(Offset Disc Harrow) or four sections Tandem Disc Harrow). When viewed from above, the four sections would appear to form an "X" which has been flattened to be wider than it is tall. The discs are also offset so that they are not parallel with the overall direction of the implement. This is so they slice the ground they cut over a little bit to optimize the result. The concavity of the discs as well as their offset angle makes them loosen and pick up the soil they cut.
Before invention of the modern tractor, disc harrows typically consisted of two sections and which were horse-drawn and had no hydraulic functionality. These harrows were often adjustable so that the discs could be changed from their offset position. Straightening the discs allowed for transport without ripping up the ground; also they were not as difficult to pull. Overuse of disc harrows (called "disc plows") in the High Plains of the United States in the early 20th century may have contributed to the "Dust Bowl".
Modern disc harrows are tractor-driven and are raised either by the 3 Point lift or hydraulically by wheels. Some large ones even have side sections which raise up vertically or fold up to allow easier road transport or better storage configurations.
Primary Heavy Duty Disc harrows of 265 to 1000 lbs per Disc are primarily used to break up virgin Land chop material/Residue an incorporate it into the \Top Soil. Lighter Secondary Disc Harrows help completely incorporate Residue left by a primary Disc Harrow, eliminate clumps and loosen the remaining soil packed soil. The Disc Notched Disc Blades chop up stover left from a previous crops, such as cornstalks. Disc harrows incorporate remaining residue into the top soil promoting rapid decay of dead plant material. Applying fertilizer onto residue on the surface of the soil contributes to a great deal of applied Nitrogen being tied up by plant material and is not available as a consequence to germinating planted Seed. Disc Harrows are also generally used ahead of a plow to make the land easier to manage and work after a plowing operation.(That is if a Plow is used) it can also reduce clogging and allow more complete turning of the soil in the plowing process.
A Disc harrow is the preferred method of incorporating Agricultural lime (Either Dolomitic or Calcitic Lime) as well as Agricultural Gypsum and achieves a 50/50 mix with the soil when set correctly, reducing acid saturation in the top Soil promoting strong healthy Root development. Lime does not move in the soil and this poses a critical challenge to sustainable Zero till operations especially where Chemical Fertilizers are generally used by Farmer around the world.
Offset Disc Harrow
The Heavy Duty Disc with large Diameter disc blades of 26" 28" 30" 32" 36"and 40" and increased Disc spacings of 10" 14" and 18" are Primary Tillage Tools used to break virgin ground incorporate residue into the soil in preparation for either a Ripper /Subsoiler to break up a compacted soil, increase soil aeration as well as the promote soil permeability to lower levels of the soil profile. Prior to a planting operation a secondary Disc Harrow with Narrow disc Spacing of 8", 9", and even 10" with disc sizes ranging from 20", 22",24",26" can be used. NB Other similar secondary Tillage Tine implement or Rotary harrow are also widely used. When considering Secondary tillage equipment soil Type must be closely observed, in conjunction with the soil moisture content at the time. Lighter secondary Disc Harrows are primarily used to break down soil clods into smaller units. By so doing it allows easier penetration of water into the soil, increases soil aeration and enhances the activity of soil biota, and the final result is a seed bed that can be planted into.
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