Modern subsoilers therefore tend to have narrow shanks, are not parabolic, and may have attachments that actually help to keep residue in place.

There are different types of subsoilers that can be used without disturbing surface residue much: Some have large winged points that heave the soil and cause much fracturing of the soil, even between shanks.

Others, such as the paratill unit, have bent-leg shanks (not common in Pennsylvania). The shanks come down straight, then curve sideways on a 45 degree angle, whereas the tip is again positioned downwards.

Research at the Soil Dynamics Lab in Alabama has shown that paratill shanks do maximum subsurface fracturing, take less power per shank than straight shanks, and do minimum surface residue disturbance.

Despite what some manufacturers may say, in my opinion, it is best to use subsoilers only under reasonably dry soil conditions. This means you should not be able to make a ball of soil by kneading it in your hand. The soil has to be that dry anywhere in the profile to the depth of tillage.

Contemporary subsoiling is meant to be a one-pass operation so that crops can be planted immediately after subsoiling without secondary tillage.

The choice of attachment is very important because it determines surface residue reduction to a large degree. Soil tends to ‘blow out’ behind the shanks (especially when run at higher speeds) so attachments are available to push soil back to create a suitable seed bed.

To achieve soil conservation goals, more than 30 percent residue cover should be present after sub-soiling and planting, so attachments should not cover residue but leave it on top.

Kick-back mechanisms are another necessity on sub-soilers. If not present, shear bolts will have to be replaced on a regular basis in our rocky soils, making sub-soiling an arduous task.

Next is the depth to which the shanks should be set. The subsoiler should be set approximately 1 inch below a compacted layer (if present). A tractor that can pull the sub-soiler needs to be available. Depending on soil conditions, you should count on approximately 40-50 HP available per shank.

Once subsoiling has been completed, it becomes necessary to have a plan in place to manage traffic after subsoiling and build soil structure. The benefits of subsoiling are easily lost by recompaction with heavy equipment. In fact, the situation will be worse than before sub-soiling, because the subsoiled field is more susceptible to rutting. Therefore, use flotation tires on all equipment and reduce tire pressure as much as possible to benefit from a large foot print.

Do not exceed 10 ton axle loads, and limit repeated traffic to select areas of the field that can then be treated if needed. After sub-soiling, plant cover crops to increase root mass in the surface and subsoil and rotate crops with different root architectures, such as tap-rooted and fibrous-rooted crops.

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