Chisel plows & Subsoilers

Chisel Plow

A chisel plow (Figure 8.9) is an implement designed for primary tillage at depths from 15 to 46 cm. The soil engaging tools are shanks equipped with replaceable points or shovels. They shatter, mix, and aerate the soil with little soil inversion. They leave a rough soil surface with most of the plant residue remaining uncovered. This condition helps prevent wind and water erosion while improving water penetration into the soil, and the plant residue on the soil surface improves traction.

Chisel plows function most effectively when the soil is dry and firm because the tools can pass through wet soil with almost no shattering action.

A chisel plow requires approximately one-half of the draft of a moldboard plow with the same working width and operating at the same tillage depth. However, farmers usually operate a chisel plow at a greater depth than a moldboard plow to break up the plow sole for improved water and root penetration. Under those conditions the draft requirement of a chisel plow increases.

Figure 8.9 – A pull-type chisel plow with rigidly mounted shanks.

The plant residue left on the soil surface acts as an insulator and slows soil warmup and soil drying in the spring compared with soil left bare from moldboard plowing. Some researchers have found a need for increased chemical application rates because chisel plowing does not bury weed seeds and because plant residue may absorb some of the chemicals.

Chisel plowing is usually completed in late summer or early fall and is followed by one or more secondary tillage operations during the following spring. Both the surface roughness and required draft increase with increased operating speed. Chisel plows are available with integral and drawn hitching configurations. The shanks are designed with spring-cushion, spring-reset, or spring-trip mountings to protect the tool and frame from impacts with buried rocks.

Subsoilers

Subsoilers (Figure 8.10) are used to break through and shatter compacted or otherwise impermeable soil layers and to improve rainfall penetration. They have heavy standards that can be operated at depths of 45 to 75 cm or more. Subsoilers do very little soil mixing and no soil inversion. They are most effective under dry and firm soil conditions. A subsoiling operation is usually followed by another primary tillage operation before secondary tillage is begun. Most subsoilers use the integral hitching configuration, but a few are available with the drawn hitching configuration. Subsoilers frequently rely on the heavy design of the frame and standards for protection during impact with buried rocks. Figure 8.10 shows a pull type V-frame subsoiler.

Figure 8.10 – A pull-type V-frame subsoiler.