Soil Resistance
The resistance the soil itself shows to the implement working it, that is, the drawbar force needed per unit of cross section. It varies with soil type, moisture and compaction even within the same field; this variation directly makes the drawbar force, the engine load and the slip fluctuate.
Sandy soils give low resistance, heavy clay and dry soils give high resistance. When moisture drops a great deal or the soil is compacted, the resistance rises quickly. When the resistance increases, an implement working at a fixed depth pulls down the engine speed, increases slip and raises fuel consumption.
- Resistance rises approximately in direct proportion to the implement's cross-sectional area and depth.
- Even a change of direction of travel in the same field can make the resistance feel different.
- Where the tractor is straining, reduce the depth first, do not force the engine speed.
Soil resistance is the reason draft control exists: when the resistance rises, the system raises the implement somewhat and holds the load constant. Electronic retrofit kits do not measure resistance and do not produce this response. If your tractor has no draft control, you have to reduce the depth by hand in hard areas; the convenience the kit provides is that you can give that command more quickly.
The context where this term is used: Converting a tractor hydraulic lever to electronic control