Agronomics

Cover Crops

Overview
Interest in cover crops has skyrocketed over the past few years across soybean production regions. In some crop production systems, cover crops are an age-old practice for maintaining soil productivity, but their use in soybean productions systems has been minimal until recent years.

The concept of “soil health” has also gained traction in recent years. Soil health, also sometimes referred to as soil quality, is defined as the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans. The definition speaks to the importance of managing soils so they are sustainable for future generations. Cover crops are an important component of soil health.

Producers are giving cover crops a fresh look as part of modern sustainable agricultural systems. Keep in mind that cover crops provide some benefit to the soil or environmental quality. They are not planted for harvest value. Some cover crops are suitable for grazing or haying, but if you plant them for such purposes, then they are forage crops and should be managed as such.

Cover crop benefits
Potential benefits to using cover crops include:

  • Scavenging or “trapping” residual soil nitrate to prevent losses from leaching into the water table.
  • When a legume cover crop is used, atmospheric nitrogen is “fixed” by root infecting synergistic bacteria. This nitrogen will eventually become available to the next soybean crop as the cover crop residue is broken down by soil microorganisms.
  • Protecting the soil surface from erosion by both wind or rain.
  • Improving soil physical properties including better tilth, increased organic matter, increased biological activity in the soil, and recycling of nutrients in addition to nitrogen.
  • Suppressing weeds by competition, shading, or the production of “allelopathic” chemicals that serve as natural herbicides.
  • Provide water, cover, and food for birds and other wildlife and increase landscape diversity. They may also provide habitat for pollinators and other beneficial insects.

Selecting appropriate covers

  • Consider your cropping/tillage system
    • In what time frames can they be planted and terminated?
  • Will you select a crop that will be cold terminated (e.g. oats) or one that will continue growth in the spring (e.g. cereal rye)?
  • How will your climate fit the cover crops selected?
    • There needs to be greater cold tolerance as you move northward.
  • What cover crops are suitable for your soil type and drainage?
    • Crops selected for clayey, poorly drained soils will likely differ from those selected for sandier, droughty soils.
  • Will you use a single species or a mixture?
    • Single species covers are easier to manage, but mixtures can provide multiple benefits and improve biological activity more quickly.
  • Consider the effects of possible herbicide carryover from the previous crop on the cover crops selected.
Photo Credit: Joseph L.Murphy

Seeding methods

  • Drilling or split-row planting
    • Good seed-to-soil contact makes these methods more reliable.
    • A disadvantage is that planting cannot occur until the cash crop is harvested.
  • Broadcast seeding with or without shallow incorporation
    • Use of shallow incorporation with a harrow or vertical tillage tool can cut and fluff crop residue allowing better seed-to-soil contact.
    • Seeding without incorporation is possible but less reliable. Certain cover crops such as peas will establish poorly without incorporation.
  • Aerial seeding/overseeding
    • Planes, helicopters, or high clearance ground equipment can be used to broadcast seed into standing crops.
    • This method can provide an earlier seeding window and more cover crop options to choose from.
    • Major disadvantages include poorer seed-to-soil contact and negative impacts from highly variable soil moisture conditions in late summer and early fall.

Cover crop termination

  • Winter kill
    • Crops such as oats and oilseed radish can be used in northern production areas since they will establish well in the fall, but will be killed out during the winter.
  • Herbicide applications
    • Always consult herbicide labels and current state recommendations about specific chemicals and crops.
    • Generally, nonselective contact products (e.g. paraquat) or translocated products (e.g. glyphosate) work well.
  • Tillage
    • Tillage can be affective but there can be challenges if there is a large amount of above ground growth.

Other Considerations
Online resources are available from the Midwest Cover Crops Council to assist in selecting the proper cover crops and mixture ratios.

Some cover crops can suppress certain soybean diseases. In University of Illinois studies, cereal rye planted after fall corn harvest and killed and incorporated into the soil in the spring prior to soybean planting, significantly reduced stand losses due to Rhizoctonia seedling blight. In a Kansas State University study, when certain mustard species that produce high levels of glucosinolates were used as a cover crop, there was a reduction in charcoal rot in the subsequent soybean crop. Other diseases that may be suppressed less consistently include sudden death syndrome, Septoria brown spot and soybean cyst nematode.

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Source: Information on cover crops is provided by Douglas J. Jardine, Professor Emeritus, Kansas State University 7/2020. Images provided by Crop Protection Network and IPM images and Joseph L. Murphy