Due to the very wet spring in 2019, farmers were forced to work their soil wetter then they prefer to be able to plant their crop. When soils are tilled when wet, soil compaction will occur. When soils are compacted they are less productive and less healthy. Compacted soils have less pore space, and that means that plant roots might not be able to “breathe,‘ and both root development and nutrient uptake are restricted. Compacted soils also do not drain properly. All of these problems ultimately impact crop yield.

Compaction is typically caused by the use of heavy equipment when soils are too wet to support the weight of the equipment. Most compaction occurs in the spring preparing a field to plant a crop and in the fall when crops are being harvested. Farmers are often faced with the difficult choice of either working on wet soils to either get the crop planted or harvested before yields are reduced, or risk causing soil compaction.

Prevention is the best way to prevent compaction. The ideal situation is to wait for soils to dry out before entering the field. If that is not possible, a plan should be developed to repair the damage before the next growing season. Soil will not heal itself.

There are three methods a farmer can use to help alleviate soil compaction. Deep tillage (12 inches or more) can break up compaction. Growing a crop such as alfalfa that has deep roots will help break up compaction. In our office we have an alfalfa root that a local farmer brought in to show us. The root is nearly two inches in diameter, and the farmer said that it was at least 15 feet long. Roots like these penetrate compacted layers and create pore spaces. The third option is to plant cover crops with deep roots, such as oilseed radishes, that will use root growth during the fall to help break up compaction. These cover crops can increase rain infiltration, reduce surface runoff, and improve both soil tilth as well as overall soil quality.

As the harvest of wheat and other small grain crops approaches and old hay stands are being rotated out, now is time to consider options for planting cover crops. Allowing a cover crop to take advantage of the remaining two to three months of favorable weather conditions can address soil compaction that may have taken place earlier in the crop rotation and negatively impacted production and soil quality. For the livestock producer, late-summer planted cover crops may provide a high quality pasture for the fall.

Selecting a cover crop for your operation comes down to assessing your goals and desired management strategies, and considering if the herbicide applications made in the previous crop may limit your options.

Selecting the right cover crop

Assistance is available for farmers in selecting a cover crop that fits their particular situation. Our staff is able to work one-on-one with farmers to find the right techniques and species for their unique conditions and crop rotations. There is also an online option. The Midwest Cover Crop Council has a tool available that will make recommendations for planting cover crops based on location, cash crops, objectives for the cover crop(s), and the soil type. You can access this tool by typing the Council’s name in a search engine.

These are the most common cover crops to consider for late summer planting that will address soil compaction include:

• Oats: Oats have good growth in cool temperatures, build soil organic matter, and make an excellent component of a multi-species cover crop mix. They may also be grazed. When planted before September first, they can be used to control weeds over the winter. Oats are not hardy, and winter temperatures will kill the plants. This can be an advantage, as no tillage or herbicides are required in the spring prior to planting crops.

• Red Clover: This common clover is a short-lived perennial lasting up to three years. It typically is planted in the spring, but it can also be planted in the late summer. Because of its strong growth, it makes an excellent soil builder. It is commonly seen in a multi-species cover crop mix. One caution is that it should not be used as a primary species for grazing, as it can cause some health issues with livestock.

• Oilseed Radish: The oilseed radish has root that can go as deep as 10 inches into the soil. The long tap root breaks up soil compaction, allowing the next crop to root deeper and thus be able to get at nutrients and water that are below the previously compacted soil layer. They have also been shown to have near complete suppression of winter annual weeds. 

Cover crop mixes

Many growers have found that by planting a mixture of cover crop species mentioned above they reap benefits that are greater than those from planting just one species. According to Paul Salon, USDA-NRCS Plant Materials Specialist working in New York, diverse cover crop mixes increase soil microbial diversity, which in turn increases the health of the soil. They are also better at suppressing weeds due to their varied growth habits. Many seed companies sell seed mixtures adapted to planting in late summer and early fall. Some companies will even customize mixtures for growers based on their soil types and the commercial crops that will be grown.

It will take up to two months of good growing conditions to gain the most benefit from your cover crop. The best seeding method to establish these cover crops is with a grain drill either in a tilled or no-till system.

If you are growing crops such as corn that are harvested later in the year, deep tillage is likely to be a more workable option to deal with compaction. The tillage should extend down to at least 12 inches deep. It can be performed in the late fall after harvest, or in the spring before planting.