Cover Crops for Vegetable Production

Published: February 15, 2021

Soil management of vegetable crops takes on added importance because of their high dollar value. Therefore, soil improvement via the use of cover crops is an important management consideration for vegetable growers. Cover crops represent an effective way to improve both the physical and chemical properties of soils dedicated to vegetable production.

A number of questions must be considered before planting cover crops. They include:

• Is the primary goal of the cover crop to fix nitrogen, suppress weeds or add organic matter to the soil?
• When will the cover crop be planted (i.e, fall, spring or summer) and how long will it take to mature?
• Does the cover crop chosen need to be able to withstand freezing temperatures?
• How will the cover crop be terminated (e.g., mowing, herbicides, etc.) so that the field may be planted?
• Will the cover crop seed itself before termination and risk becoming a weed?
• What cash crop will be planted after the cover crop?

Additionally, growers must be aware of the advantage and disadvantages of various cover crops available for use. For example, legumes, such as clover, hairy vetch, Austrian winter pea and others do a good job of fixing nitrogen, but they don't leave high amounts of residue or contribute greatly to soil organic matter. However, since most vegetable crops require between 100 and 220 pounds of nitrogen per acre, the use of legumes as cover crops can help supply a substantial portion of nitrogen fertilizer requirements.

Alternatively, grasses such as cereal rye, Japanese millet and others produce a lot of biomass and build soil organic matter more rapidly, but they don't fix nitrogen. Additionally, they can tie up nitrogen in soils due to their high carbon-to-nitrogen ratio. Tillage radish and buckwheat neither fix nitrogen or produce abundant residue. However, each serves a function of its own.

The majority of vegetable growers employ fall-planted cover crops, since most of their available land is occupied during the growing season by vegetables. That said, there are several major considerations for fall-planted cover crops. For example, for larger, transplanted crops such as tomato and pepper, a cover crop that can be terminated and left on the soil for mulch and weed suppression might be the best choice. Alternatively, cover crops that are low residue such as tillage radish can be planted directly into the following spring, or incorporated into the soil and then planted.

Fall seeding of cover crops most generally occur from mid-August until mid-September. This allows for an adequate time to achieve the maximum amount of growth. Cereal rye can be planted until Thanksgiving. Some simple options like tillage radish are worth trying, especially for growers who have not planted cover crops before. Tillage radish leaves very little if any residue left on the soil.

Oats is another common cover crop used in vegetables systems. However, it will winter kill and leaves low residue. It often is combined with Austrian winter pea, which is able to fix nitrogen. Hairy vetch is a winter annual that can be planted in the fall and terminated in the spring, using a variety of different methods. Cereal rye is also a winter annual often used as a companion plant to hairy vetch.

The establishment of a cover crop is just as important as the establishment of a cash crop. Cover crop seed germination will be enhanced through good seed-to-soil contact. This can be accomplished through mechanical preparation of the soil, or through the use of hand tools to help rough up the soil surface. Additionally, it is important to remove or kill weeds before planting cover crops, since the latter find it difficult to compete with already established weeds. When legumes are used as cover crops, it is important to remember that different species might require different bacterial inoculant species. Therefore, make sure to purchase the appropriate inoculant for the cover crop being seeded to ensure maximum nitrogen fixation.

Cover crops may be seeded by broadcasting seeds by hand, through the use a belly seeder, or a fertilizer spreader. Drop seeders/spreaders and powered broadcast spreaders represent another option. In any case, covering the seed will also help to enhance seed germination and establishment. The latter can be accomplished through the use of tractor tools such as light harrow, cultipacker or a firmer/roller. Growers also might consider spreading a light layer of compost on top of the seeds, if covering the seeds using the above mentioned options isn't possible. Seeds should be watered in well, especially if the soil is dry. In the absence of rain, irrigation should be considered to help seeds germinate.

The following comprehensive chart was taken from Managing Cover Crops Profitably published by the Sustainable Agriculture Research and Education (SARE) program.

Managing Cover Crops Profitablyis one of the most comprehensive resources on cover crops for use both in row crop production, vegetable production as well as perennial crops. It can be viewed online or downloaded from the internet by going to the following web address: https://www.sare.org/wp-content/uploads/Managing-Cover-Crops-Profitably.pdf. Individuals who lack internet access may obtain a copy by sending a check for $25.95 payable to SARE Outreach Publications to: SARE Outreach Publications, c/o International Fulfillment Corp., 3570 Bladensburg Road, Brentwood, MD 20722.