Disks can be used in cultivation either as a primary tillage equipment-Disk plow or as a secondary tillage equipment-Disk harrow. The disk plows are used for plowing (intensive tillage), whereas disk harrows are used for smoothing the plowed soil surface to prepare good soil tilth for planting. Disks can be made part of a mulch tillage system (minimum tillage management using conventional tillage equipment) wherein the residue cover is maintained above 30%. This post will concentrate more on the disk harrows that can be used in minimum tillage and briefly mention the disk implements currently used for primary tillage. 

Disk harrows consist of concave metal disks (cutting blades) set at an oblique angle, either with a smooth edge or scalloped edge (small curves along the edges). Smooth edge disks can be used in normal soil conditions for leveling purposes, and scalloped edge disks can help in heavy residue conditions, wherein they help cut and chop up weeds and residues on the soil surface. The disks can vary in their blade sizes and spacing, extent of concavity, material with which they are made (carbon steel/boron steel), and arrangement. Regarding sizes, disks can have diameters ranging from 20 cm (light) up to 60 cm (heavy). Disks can be arranged into two classes: single-action and double-action. 

Single action disk harrow consists of two disk sections/gangs arranged end to end at an angle. The disk sections are arranged so that they throw soil in opposite directions. The right gang of disks throws the soil toward the right, and the left gang throws them toward the left. 

The double-action disk harrow can have two or more disk sections/gangs set one behind the other. When one disk gang is arranged after another at an offset angle on a single side (a total of two disk gangs), it makes an offset disk arrangement. They can be either on the left or right side of the line of travel. When this setup is repeated on the other side as well, that forms a tandem disk arrangement having a total of four disk gangs, creating a flattened shape X when viewed from the top. The four sections of disks are arranged with an offset angle, making sure they are not parallel to the direction of movement of the implement. This arrangement also ensures that on each side of the line of travel, the soil is thrown in opposite directions as the disc gangs on a single side face opposite directions. Tandem disk implements are commonly employed in heavy residue crop cultivation, such as corn. 

The disks arrangement can be changed in accordance with the extent of residue and soil slicing required in your field condition. The amount of residue left on the soil surface after disks are run can depend on the type of crop being grown. If the crops have heavy residue (corn, sorghum, wheat, etc.), a single disk pass can still leave around 40-70% residue. At the same time, if the crops have fragile residue, a disk run can bury the residues and not provide sufficient coverage. Therefore, it is essential to finetune the disk tillage practice suited to your crop production system. In any case, the disk equipment passing must be limited to one for a chance of residue coverage and erosion control. A field cultivator is sometimes used as a follow-up secondary tillage practice. The time gap and extent of weathering between disking and field cultivator passing can cause differences in the extent of residue coverage. Disk implements can also be used for incorporating herbicides and fertilizers; however, it should be made sure that the disks are not run in wet soils, as this can cause uneven application. Disking under wet conditions can also create undesirable results like clod formation that would require further tillage and compaction issues that can impair root growth. The timing of disk tillage operation should be adjusted so that the chances of wind and water erosion are minimal, depending on the soil type and weather conditions. 

Disk rippers and disk chisels are the most used primary tillage implements. Disk rippers have discs and heavy shanks running to deeper depths. The disks assist in chopping and rolling the soil, and the shanks running behind help with the soil loosening. They can bury up to 70-80% of residues and require up to 50 horsepower per shank. The operating width, depth, and angle can determine the extent of horizontal shearing caused. Disk chisels have disks and chisel shanks, with the chisel shanks running behind discs and set below disk level. This arrangement of chisels facilitates the removal of the density layer (looser topsoil and firmer subsurface soil) caused by the disks running in front. It can be used in crop production systems with heavy residues, as they can bury up to 50-75% of residues, with a 20-30 horsepower requirement per shank. Disc chisels cause horizontal shearing and rectify them in a single pass; hence, they can be considered a vertical tillage practice. 

Disk tillage can be fit into the conventional or conservation tillage category based on the purpose for which it is used, the amount of residues required, soil erosion control, and soil quality maintenance that can ensue with variations in the adoption intensity. To sustainably apply this approach per your soil condition and requirements, join our extension and education activities.

Please check for factsheets that involve studies with disk tillage.

Soil Health: What Does it Mean in North Carolina? 

Long-Term Tillage Effects on Corn and Soybean Yield in the Piedmont