Depth Accuracy on a Seed Drill
Keeping the depth at which the seed is placed in the soil constant across the field. When the depth varies from row to row, germination times separate from each other and plant emergence loses its uniformity. That is why in seeding the target is constant height, not constant draft force.
On seed drills the depth is mostly determined by the machine's own press wheels or depth limiters; the job of the three-point linkage is to hold the machine at the correct height and at a level angle. If the linkage forces the depth, the press wheels lose their function.
- In seeding, position control is preferred; draft control makes the depth fluctuate.
- The top link adjustment sets the machine's fore-aft level, and the lift rods set its lateral level.
- Raising and lowering the machine at the same point every time on the headland reduces gaps and overlapping seeding at the row ends.
The contribution of electronic control here is repeatability. Instead of bringing the quadrant lever to the same notch by hand on every pass, the same command is applied with a switch or joystick; on the LFT20 and LFT54 the cable is pulled to the same stroke every time (60 mm / 50 mm). This does not measure the depth, but it reduces operator-induced deviation.
Context in which this term is used: Converting a tractor hydraulic lever to electronic control