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Manure, compaction and cover crops

Soil compaction is when pressure decreases the spaces between soil particles. When soils lose pore space, they have a reduced ability to hold water and air which is essential for plant growth. In many cases, when there is a compaction issue at a certain depth or on the sidewall from planting the plant root’s ability to grow is affected. Limited pore space also reduces water’s ability to infiltrate the soil and properly drain, which can lead to ponding issues or additional runoff, an increase plant injury from soil applied herbicides, yield reductions and other issues which last years.

Most soil is susceptible to compaction. Compaction can be caused or exasperated by many factors including equipment traffic and size, tillage practices and field conditions. Sandier soils are less susceptible to compaction but can become compacted, while heavier soils are much more likely to become compacted due to their smaller particle size. Compaction can happen at distinct levels: surface crust, surface, tillage pan, subsoil.

How do I prevent compaction in my fields?
Manure itself can help alleviate compaction issues in the long term as it helps build soil organic matter and soil structure. However, application can cause compaction when not managed correctly. Manure is often applied in the fall and spring (except for into hay fields, following wheat) when fields are sometimes wetter than other seasons in Michigan. Avoiding trafficking saturated fields is the best way to prevent compaction.

Some best management practices to reduce the incidence of compaction in fields, according to Linda Schott at the University of Idaho, include making mindful equipment choices, using reduced tire pressures, and using traffic control.

Bigger tires are great, but if the contact area has not increased compaction is still a risk. Tire volume needs to be managed to get more contact area to reduce compaction. One way to do that is with a central inflation system and knowing the recommend pressure for your tires for the road and for the field.

Traffic control limits agricultural machinery traffic to designated areas, rather than across a whole field year after year. This restricts compaction to zones, while the seedbed remains undisturbed. According to the Natural Resources Conservation Service (NRCS), to accomplish controlled traffic the following must be accomplished:

• Ensure that controlled traffic lanes are designed and used to avoid concentrated flow that may result in gully erosion.
• Limit wheel/track traffic to no more than 30 percent of the soil surface.
• The same tracks must be used for all high load traffic continually.
• Use a Geographic Positioning System (GPS) to guide field operations and wheeled/track traffic when the designated traffic lanes are obscured.
• Once the tram lines or traffic pattern is established, do not till deeper than four inches.

What can I do if my field has soil compaction?
Certain things can help the overall soil structure, including cover crops, building organic matter, changing management practices to avoid working the field when wet, controlled traffic and thoughtful equipment choices.

Soils are resilient and can repair themselves if left to their own devices; however, this typically means a fallow period. We can help them repair themselves by changing our management practices to help them develop in a way that is more favorable to rebuilding that soil structure.

When choosing cover crops, it is important to choose the right type of rooting system. In extreme cases of compaction, such as after construction activities, a pass of deep tillage may be needed before planting. A deep-rooted crop such as oil seed radish or cereal rye helps break up compaction deeper into the soil profile, while cover crops with a more fibrous root system such as oats and buckwheat will help break up crusting toward the top. Either way, getting living roots in the soil helps to create organic matter and pore space when they are terminated and decompose. •