By Sjoerd Duiker, Soil Scientist
You may be wondering if you should use a subsoiler to alleviate soil compaction. Subsoiling can be consistent with “Conservation Agriculture” as long as it does not invert the soil and leaves most residue at the soil surface, while fracturing the soil underneath. Our research has shown that subsoiling is not justified in long-term no-tillage on most of our soils. The exception to this is when extreme compaction has been caused. Compaction can be perfectly managed using cover crops and flotation tires in long-term no-tillage.
Before you pull out the subsoiler, therefore, take a shovel and check soil aggregation and porosity. If the soil is well-aggregated and does not show severe platiness or massive structure, subsoiling is unlikely to result in any benefit. Instead, it will make the soil more sensitive to re-compaction and rutting and will make the soil surface rough, which can pose future issues with drilled crop establishment.
That being said, our research on a long-term no-tilled field with a shallow fragipan (Andover series) showed a yield bump in continuous corn. In our trial, the yield response was 14 bushels per acre from subsoiling of continuous no-till (without intentional compaction).
To get good results, use the subsoiler when soil is dryer than the “plastic state” (when you can make a ball out of soil). Plant right on top of or close to the slot you created. Make sure the subsoiler does not create a very uneven soil surface. This can be assured by using a subsoiler with straight shanks and some type of attachment to avoid soil “blowout” next to the shank or other attachment to break up clods or push them back into the soil. You need a tractor with about 40 hp per shank to pull a subsoiler set at 15-17 inches in depth.