Too Much of A Good Thing?
March 14, 2025
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Agriculture faces many challenges ranging from soil degradation to weed pressure and nutrient depletion. One promising solution to these challenges is the use of cover crops. Cover crops grown primarily for ground cover rather than harvest provide multiple advantages such as enhancing soil health, suppressing weeds, and promoting sustainable farming practices.
What are cover crops?
Cover crops are plants grown during fallow periods or between cash crop cycles to protect and enrich the soil. Examples of cover crops that can be used in Missouri includes cereal crops, brassicas, grasses and legumes. Table 1 provides the list of common warm and cool season cover crops that can be used in the Midwest region.
Termination of cover crops
Cover crops must be fully terminated before or shortly after planting cash crops. If not properly managed, they can compete with cash crops for moisture, sunlight, and essential nutrients, effectively acting as weeds. Two most common method of terminating cover crops are chemical and mechanical.
Starting with the crop year 2020, crop insurance for the insured crop also provides cover crop management practices that is evaluated under Risk Management Agency (RMA) rules for Good Farming Practice (GFP) determinations, similar to other management decisions such as fertilizer application and seeding rates. Deciding when to terminate the cover crops is a balancing act between maximizing biomass production to enhance cover crops soil benefits and minimizing potential risk to cash crop planting, emergence and yield.
More information on cover crop termination guideline provided by USDA NRCS can be found in the link below:
Benefits of Using Cover Crops
The benefits of cover crops cannot be overstated. Governmental organizations like USDA NRCS are dedicated to disseminating information on adoption of cover crops in farms because of many benefits that cover crops can offer.
Major benefits of cover crops include:
1) Improvement of soil health which ultimately leads to yield increaseCover crops improve soil health by increasing organic matter content of the soil. They increase organic matter as they decompose, enhancing soil structure and improving its ability to retain nutrients and water. This organic matter also supports the growth of beneficial soil organisms, such as earthworms and microbes, which further enrich the soil. Additionally, cover crops enhance nutrient cycling by fixing nitrogen, especially in the case of legumes, and making it available to other plants. As cover crops decompose, they also release other essential nutrients, like phosphorus and potassium, into the soil. Cover crops keep the soil covered reducing the chances of soil erosion and nutrient leaching during heavy rainfall.
2) Soil moisture conservation
Residues after cover crop termination reduces evaporation from the soil surface and increases water infiltration rate resulting in less moisture stress during elongated drought period. However, timely termination of cover crops is essential to avoid negative impacts of cover crops on soil moisture. Excessive cover crops residue can retain too much moisture in wet years while actively growing cover crops may deplete soil moisture during dry years.
3) Weed suppression
Cover crops play a crucial role in weed suppression by utilizing multiple mechanisms to outcompete and inhibit weed growth. They compete with weeds for essential resources such as sunlight, water, and nutrients, making it difficult for weeds to establish and thrive. Some cover crops, like rye and mustard, release allelopathic chemicals that suppress weed seed germination and growth. Additionally, the dense canopy formed by cover crops shades the soil, reducing light availability for weed germination, while their residues after termination create a mulch layer that further inhibits weed emergence.
4) Mitigate insect, disease and nematode pressure
Cover crops help reduce diseases, pests, and nematodes through several ecological and biological mechanisms. Cover crops act as a barrier, interrupting pest life cycles by providing habitat for beneficial insects and natural predators that help control pest populations. They also reduce soil erosion and improve water infiltration, creating conditions less favorable for pathogens that thrive in compacted or waterlogged soils. Some cover crops, like castor bean and sorghum-sudan grass, have specific nematode-suppressing properties, disrupting nematode reproduction and reducing their populations. By incorporating diverse cover crop species into crop rotations, farmers can naturally mitigate pest and disease pressures while enhancing overall soil health and resilience.
5) Promote sustainable and resilient farming systems
Cover crops enhance environmental resilience and sustainability by improving soil health, reducing greenhouse gas emissions, and increasing a farms ability to withstand extreme weather events. By adding organic matter and enhancing soil structure, cover crops improve water infiltration and moisture retention, making soils more resistant to droughts and heavy rainfall. They also prevent soil erosion, reducing the loss of topsoil and nutrients during extreme weather conditions. In terms of greenhouse gas reduction, cover crops help sequester carbon in the soil, lowering atmospheric CO₂ levels. They also decrease the need for synthetic fertilizers by fixing nitrogen (in the case of legumes) and cycling nutrients, which helps reduce nitrous oxide emissions, a potent greenhouse gas. By naturally suppressing weeds, cover crops minimize the need for herbicides facilitating reduced chemical use. Cover crops further support biodiversity by providing habitat for beneficial insects, pollinators, and soil microorganisms, contributing to a more resilient agroecosystem. By incorporating cover crops into farming systems, growers can improve long- term soil health, boost productivity, and create a more sustainable agricultural system.
USDA NRCS Cover crops guidelines
The NRCS cover crop guidelines, found in Conservation Practice Standard Code 340, focus on establishing and managing cover crops to enhance soil health and reduce erosion, with specific guidelines for planting, termination, and management.
More resources on cover crops provided by USDA NRCS can be found in the link below:
written by Swati Shrestha, PHD
“This material is based upon work supported by the U.S. Department of Agriculture, under agreement number NR226424xxxxG003.Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the U.S. Department of Agriculture. In addition, any reference to specific brands or types of products or services does not constitute or imply an endorsement by the U.S. Department of Agriculture for those products or services. USDA is an equal opportunity provider, employer, and lender.
