By Sjeord Duiker, Soil Scientist
It has been unseasonably warm and dry lately in Pennsylvania. Dry soil means the threat of soil compaction is limited. With rain in the forecast, a great window of opportunity is open to plant soil-compaction-busting cover crops, such as forage radish, annual ryegrass, and rape after corn silage, high-moisture corn and early soybean harvest, while still having plenty of opportunity to plant the ‘workhorses’ — cereal rye, wheat and triticale. It’s also an opportunity to improve soil fertility and biological activity with the overwintering legumes hairy vetch, crimson clover, and Austrian pea.
All of these cover crops can be planted in mixtures according to your needs. It is not recommended at this time to plant cover crops such as red clover, sweet clover or summer annuals, such as sorghum, sudangrass, millets, buckwheat, sunflower, soybeans and cowpeas, because their opportunity to put on growth before and over the winter is limited.
The dry soil conditions also open a great window of opportunity to address severe compaction issues using subsoiling. Subsoiling is only recommended if there is a severe compaction issue. It is much better to build soil with cover crops, but in some instances it may be justified to pull out, or better yet, hire someone else with, a subsoiler.
Where we have seen a yield response to subsoiling includes cases of severe soil compaction on well-drained soils caused by harvest or manure-spreading operations. We have also seen a yield benefit to subsoiling soils with shallow fragipans reported in July.
It is not possible to use a penetrometer right now because the soil is too dry, but you can use a shovel and inspect the structure of the soil. Look for massive or platy structure that restricts root growth, inhibits biological activity and keeps water from percolating. If the soil can be broken apart and comes out crumbly or in little units called peds, there is not likely to be a benefit to subsoiling.
Subsoilers should fracture the soil and this is only possible if the soil is relatively dry. Subsoiling wet soil can decrease yields so the importance of soil moisture cannot be emphasized enough. Subsoilers should not turn up subsoil or invert the soil, and should do a ‘one pass job’ — attachments such as rolling baskets, packer wheels, coulters, rolling harrows can create a smooth soil surface ready for planting. Make sure a coulter precedes subsoiler shanks to cut through residue to avoid raking up stalks. Also, make sure the subsoiler has trip mechanisms to avoid breaking or bending shanks on rocks.
Immediately after subsoiling, plant a cover crop to build soil structure. Remember, subsoiling only breaks up compacted soil to allow air and water to penetrate and open passage ways for biological activity. Roots are among the most important partners to build soil. Remember that the soil will be very soft after subsoiling, so be very careful when taking heavy equipment into these fields to avoid re-compacting the soil. We found that re-compacting the soil after subsoiling destroyed all its benefits.