A Toolbox for Understanding and Implementing Cover Crops in your Farm or Garden

Written by Dr. Todd DeZwaan

Cover crops are a powerful tool for enhancing soil health, reducing production costs, and promoting environmental sustainability for both large commercial producers and smaller market gardens. They can reduce input costs associated with fertilizers, herbicides, and pesticides while improving soil health and preventing erosion. Cover crops also conserve soil moisture and protect water quality.

Cover crops can reduce fertilizer costs by adding nitrogen to the soil and improving the availability of essential micronutrients. Leguminous cover crops, such as hairy vetch and crimson clover, fix atmospheric nitrogen, converting it into a plant-available form in the soil. Subsequent production crops can utilize this nitrogen, allowing growers to decrease their synthetic nitrogen fertilizer applications. Non-leguminous cover crops, particularly cereals and grasses, scavenge excess nitrogen and micronutrients remaining after harvest, preventing nutrient loss through leaching and runoff and holding them within the plant biomass for later release upon decomposition.

Cover crops reduce the need for herbicides and pesticides by suppressing weeds through competition for light and soil resources, and through the release of natural herbicidal compounds. They also help manage pests and diseases by fostering a healthy soil environment. Cover crops support beneficial soil microbes that inhibit disease, create unfavorable conditions for soilborne pathogens, and attract beneficial insect predators and parasitoids that control pest populations. Brassica cover crops, such as tillage radish, can reduce nematode pest numbers by releasing compounds that break down into toxic sulfur-containing products.

Cover crop roots improve soil health by enhancing water infiltration, alleviating soil compaction, and improving overall soil structure. They increase soil organic matter and that stimulates beneficial microbial activity and enhances nutrient recycling. The quick growth of cover crops prevents soil erosion by providing a protective layer that holds soil in place, reduces crusting and shields soil against wind and rain impact. Long-term cover crop use increases water infiltration and reduces runoff, minimizing the loss of topsoil, and cover crop residue conserves soil moisture by increasing water infiltration and reducing evaporation. By reducing erosion and runoff, cover crops protect watersheds by minimizing nonpoint source pollution from sediments, nutrients, and agricultural chemicals. Their ability to take up excess soil nitrogen can also reduce nitrogen leaching into groundwater and watersheds (1).

While cover crops have significant potential to produce these benefits, many of them may only be seen after long-term investments and not after a single year of use (2). Cover crop adoption is a behavioral change, requiring significant time and commitment. Cover crops also come with risks and challenges that can diminish their success. Several resources are available to help growers implement cover crops into their operation, and understand the best practices and risks associated with cover crops.

Cover Crop Species Selector: The Cover Crop Species Selector (https://covercrop-selector.org/) helps growers choose the right cover crop species or mixes based on their specific goals and growing conditions. This tool allows growers to define their specific objectives (e.g., nitrogen fixation, weed suppression), their location and climate, and their soil type and drainage. The Cover Crop Species Selector simplifies decision-making by filtering and ranking potential species based on grower input. This tool also helps growers avoid potential pitfalls of selecting cover crops that are poorly adapted to the local climate, are difficult to manage, or fail to provide the intended benefit. 

Cover Crop Seeding Rate Calculator: The Cover Crop Seeding Rate Calculator (https://covercrop-seedcalc.org/) follows on the Cover Crop Species Selector tool. Once a grower has selected their cover crop species or mixes, this tool may be used to calculate seeding rate based on location, site conditions, and cover crop planting date. If a cover crop mix is desired, the tool will calculate the appropriate seeding rate for each species in the mix considering variables such as seed size, projected germination rate, and species competition within the mix. Using pricing input from the grower, a cost calculator returns the total amount of seed a grower needs for their operation, and the price per acre and the total cost they can expect to pay for their cover crop seed. 

Cover Crop Economic Decision Support Tool: The Cover Crop Economic Decision Support Tool (DST) (https://covercrop-econ.org/) is designed specifically for commercial growers to help them understand the economic impact of cover crops on profitability when making their seasonal crop management decisions. Following on the Cover Crop Species Selector and the Cover Crop Seeding Rate Calculator, this tool allows commercial growers to provide all their input costs and projected outputs to create a budget table that describes the total economic benefit of the cover crop. The Cover Crop Economic DST is very detailed. Inputs consider costs associated with labor, fuel, seeds, seedbed preparation, termination, tillage, fertilizer, and herbicides. Outputs include the cover crop nitrogen credit, erosion control cost savings, cover crop grazing revenue, projected yield improvement, and additional considerations such as federal assistance programs and carbon offset programs. The ‘Resources’ link (https://covercrop-econ.org/#/Resources) at the Cover Crop Economic DST provides a wealth of resources to assist with decisions on the use of cover crops and educate growers on conservation practices and soil health. 

Cover Crop Nitrogen Calculator: The Cover Crop Nitrogen Calculator (https://covercrop-ncalc.org/) allows growers to calculate their seasonal nitrogen credit from their selected cover crop. The tool relies on data collected from cover crop plant samples collected on the termination date. The minimum data required for the tool are field location, cover crop dry weight, and cover crop nitrogen concentration. Additional data on cover crop chemistry and water content at termination will increase the accuracy of the calculations. The Cover Crop Nitrogen Calculator uses real-time weather data and five-year historic averages where data is not yet available, daily soil moisture and temperature, and local soil properties to return a detailed view of the amount and timing of nitrogen and organic matter availability from a cover crop. 

Additional Resources: In addition to these decision tools and calculators, there are several resources to help growers learn more about cover cropping strategies within North Carolina and the Southern US region. The NC State Extension Cover Crop (https://covercrops.ces.ncsu.edu/) and NC State Extension Soil Health and Management (https://soilmanagement.ces.ncsu.edu/) homepages provide links to cover crop specialists, publications, and additional support tools. The Southern Cover Crops Council (https://southerncovercrops.org/) provides cover crop resources targeted to southern growing regions, including a detailed Southern Cover Crop Variety Trial report. Finally, the NC Organic Commodities Production Guide includes a chapter on best agronomic practices for rolled cover crop mulches in organic commodity crop production (https://content.ces.ncsu.edu/north-carolina-organic-commodities-production-guide/chapter-8-rolled-cover-crop-mulches-for-organic-corn-and-soybean-production).

1. SARE Outreach. (2007) Managing Cover Crops Profitably, 3rd Edition. https://www.sare.org/wp-content/uploads/Managing-Cover-Crops-Profitably.pdf
2. Stowe, K. D. (2017). NC Field Report: Thinking About Cover Crops? NC Soybean Producers Association. https://ncsoy.org/article/thinking-cover-crops/