Cover Crops

Definition

Cover crops can be legumes or grasses, including cereals, planted or volunteered vegetation established prior to or following a harvested crop primarily for seasonal soil protection and nutrient recovery. Cover crops protect soil from erosion and recover/recycle phosphorus in the root zone. They are grown for one year or less.

Purpose

To control erosion during periods when the harvested crop does not furnish adequate soil cover.
To recover phosphorus and other nutrients in the root zone by plant uptake.
To improve infiltration, thus reducing surface runoff from the soil.

How Does This Practice Work?

Cover crops are established during the non-crop period, usually after the crop is harvested, but can be interseeded into a crop before harvest by aerial application or cultivation.

Cover crops can reduce phosphorus transport by reducing soil erosion and runoff. Both wind and water erosion move soil particles that have phosphorus attached. Sediment that reaches water bodies may release phosphorus into the water.

The cover crop vegetation recovers plant-available phosphorus in the soil and recycles it through the plant biomass for succeeding crops. The soil tilth also benefits from the increase of organic material added to the surface.

Growing vegetation can promote infiltration and roots can enhance percolation of water supplied to the soil. This can reduce surface runoff. Runoff water can wash soluble phosphorus from the surface soil and crop residue and carry it off the field.

Where This Practice Applies and Its Limitations

Cover crops are suited for use in any cropping system where there is opportunity for ample vegetated development, canopy and roots, before cold or dry weather to protect soil surface from detachment of soil particles by erosion or runoff. Good plant development is essential for uptake of available phosphorus.

Use caution in situations where cover crop vegetation could deplete soil moisture prior to seeding the succeeding crop. Actively growing cover crops can pump water out of the soil by transpiration, thereby modifying soil moisture during wet periods.

Inadequate canopy cover or stem density of the vegetation will not provide sufficient soil protection or runoff reduction. A minimum of 50 percent canopy cover and 200 stems per square foot are required to produce the desired effects.

Cover crops can increase soluble phosphorus loss in surface runoff. Dead cover crop biomass can be a source of phosphorus to runoff water, especially in climates with snowmelt runoff. Conservation practices that control soluble phosphorus loss should be used in conjunction with cover crops, such as soil testing, phosphorus balance, and management of phosphorus sources, timing, and placement.

Effectiveness

With adequate vegetated soil cover, the erosion is greatly reduced. Reduction of erosion will correspondingly reduce particulate phosphorus transport. Depending on soil properties and cover crop management, cover crops can promote infiltration of precipitation into the soil profile, reducing runoff and phosphorus loss.

Overall cover crop effectiveness for reducing phosphorus loss is a balance between decreased particulate phosphorus loss and potentially increased soluble phosphorus loss. Effectiveness will be greater in cropping systems that are prone to greater erosion and particulate phosphorus loss.

Cover crops’ effectiveness in recycling phosphorus depends on the duration of growth and time of planting. The longer the plant grows, the more phosphorus accumulates in the biomass. Ranges of phosphorus in the above ground biomass, including harvested material and plant residue, is 10 to 30 pounds per acre.

Cost of Implementing the Practice

The cost of establishing cover crops includes seedbed preparation, seed and planting. Additional cost is connected with harvesting the vegetation or killing the vegetation for preparation of succeeding crops. The cost of harvesting may be offset by the value of the forage. Cost of establishment and maintenance for each cover crop ranges from $20 to $80 per acre.

Operation and Maintenance

A cover crop needs to be seeded to a density high enough to protect the soil surface by plant canopy and have sufficient stem density to retard runoff and promote infiltration. Timely planting is important to minimize the time interval between crop harvest and cover crop establishment. Weed control is required to prevent invasion of problem pests to the cropped area.

Ending the growth of a cover crop is critical because of the importance of moisture conservation for the succeeding crop. The timing of harvesting the cover for forage should be accomplished to both conserve soil moisture and produce a quality forage.

Termination of the cover crops is usually performed before seeding of the subsequent crop. This can be done by mowing, tillage, roller chopping, application of herbicides or relying on temperature extremes.

References

Local Cooperative Extension crop budgets can be referenced to determine local cost. USDA-NRCS and Extension Service technical references and standards (Cover Crop, code 340) are available at local county offices.

Blanco-Canqui, H. (2018). Cover Crops and Water Quality. Agronomy Journal, 110(5), 1633–1647. https://doi.org/10.2134/agronj2018.02.0077

Kladivko, Eileen J. (2020). Cover Crops: Progress and Outlook. In J. A. Delgado, C. J. Gantzer, & G. F. Sassenrath (Eds.), Soil and water conservation: A celebration of 75 years (pp. 293–302). Soil and Water Conservation Society. https://www.swcs.org/resources/publications/books/soil-and-water-conservation-a-celebration-of-75-years

Kleinman, P. J. A., Osmond, D. L., Christianson, L. E., Flaten, D. N., Ippolito, J. A., Jarvie, H. P., Kaye, J. P., King, K. W., Leytem, A. B., McGrath, J. M., Nelson, N. O., Shober, A. L., Smith, D. R., Staver, K. W., & Sharpley, A. N. (2022). Addressing conservation practice limitations and trade‐offs for reducing phosphorus loss from agricultural fields. Agricultural & Environmental Letters, 7(2). https://doi.org/10.1002/ael2.20084

Myers, R., Weber, A., & Tellatin, S. (2019). Cover Crop Economics: Opportunities to Improve Your Bottom Line in Row Crops. Sustainable Agriculture Research and Education (SARE). https://www.sare.org/resources/cover-crop-economics/

For Further Information

Contact your local soil and water conservation district, USDA-NRCS or Cooperative Extension Service office. To find your local USDA Service Center, visit https://www.nrcs.usda.gov/contact/find-a-service-center. Cost-share may be available for seeding cover crops from the Consolidated Farm Service Agency (CFSA).

Current Author

Nathan Nelson
Kansas State University
nonelson@ksu.edu

Previous Author

Jerry Lemunyon
USDA-NRCS

Editing and Design

Deanna Osmond
NC State University

Forbes Walker
University of Tennessee

Citation:

Nelson, N. 2023. Cover Crops. SERA17 Phosphorus Conservation Practices Fact Sheets. https://sera17.wordpress.ncsu.edu/cover-crops/