Cover cropping is becoming a practice used by many farmers for its benefits to soil health and sustainable agriculture. Cover crops are crops that are commonly planted after the primary cash crop is harvested in order to avoid periods of bare soil. Sometimes cover crops are planted before the cash crop harvest to extend the growing season for the cover crops. Cover crops offer several important ecosystem services, as well as improved yield and quality of subsequent crops. There are many different crops that are used as cover crops and each type offers their own strengths. Specific cover crops can be grown alone or can be grown in mixtures to gain maximum benefits, as well as shape the mixture to the specific needs of the agricultural system. Legumes, such as clovers and vetch, are known for their association with nitrogen-fixing microorganisms and their ability to increase soil organic matter. Grasses, such as ryegrass, barley, and cereal rye, are well known for their ability to prevent erosion, suppress weeds, and capture residual nutrients. Brassicas, such as canola, rapeseed, daikon radish, turnips, and mustards, are commonly implemented as cover crops for their benefits in erosion control, weeds suppression, water conservation. In addition, their deep and strong taproots can alleviate soil compaction and take up nutrients deep in the soil profile that the cash crops left behind.

Mixture of cereal rye and dailon radish. Photo by Nora Doonan, UConn

Cover cropping is a useful tool for preventing the leaching of nutrients because pf their ability to take up the residual nutrients. Non-legume cover crops, like grasses and brassicas, are commonly used to withdraw nutrients from the soil to be used for biomass that would otherwise be susceptible to leaching. Mixtures of legume and non-legume cover crops are a great method for both supplying the soil with nitrogen through biological N fixation by legumes and the capturing of that nitrogen by non-legumes. After the cover crops are terminated, the residue will decompose overtime and some of the nutrients will be released becoming available for subsequent cash crops.

Growing cover crops can increase soil organic carbon. Soil is one of the major reserves of carbon on land. Using cover crops for their benefits in carbon sequestration can help to mitigate climate change by removing excess CO2 from the atmosphere via photosynthesis. The rate and amount of carbon accumulation in soil from cover crops depend on several factors, such as cover crop biomass production, the number of years in which cover crops have been implemented into the system, tillage practices, the species of cover crop, initial soil organic carbon, climate, etc. In order to enhance the potential of cover crops to sequester carbon, biomass production is one of the most important factors. It is necessary to ensure that the cover crops have maximum number of growing days possible. This can be achieved by planting your cover crops immediately after cash crop harvest and terminating cover crop late or at the subsequent crops’ planting. Another practice related to biomass would be to interseed cover crops with standing crops.

Single species of cereal rye in fall. Photo by Nora Doonan, UConn

There are a few methods commonly used for cover crop termination, including natural winter kill, chemical termination, incorporation, burning and mechanical termination (such as rolling/crimping). Cover crops may also be grazed or harvested as silage. When rolling/crimping method is used, it is important that the cover crops are terminated at the right growing stage because it impacts the efficiency of killing the cover crops. For example, more than 90% rye was killed if terminated at milk stage compared with 20% rye kill if terminated at flag leaf stage, three weeks after rolling/crimping. Regrowth can occur if mowing in early growth stages. Herbicide termination is more flexible in terms of when the cover crops can be terminated. Burning can cause loss of carbon, nutrients, and turn soil surface to be hydrophobic.

Cover cropping, specifically multi-species mixtures, are an excellent method for increasing agroecosystem diversity, which serves many benefits in weed and pest management and nitrogen retention. Whether grown as a single species stand or in polyculture, it is clear that cover crops can be used as a tool to achieve specific goals necessary for promoting soil health.

Home gardeners can practice cover cropping on a smaller scale. Winter rye, buckwheat, oats, beans, peas and some alfalfa species can be planted before, during or after harvest depending on the purpose of the cover crop.

Nora Doonan, Graduate Research Assistant, University of Connecticut