Cover Crops 101
Recently I received two calls from growers who are interested in being able to “grow” a significant proportion of the nitrogen that next year‟s corn crop will need. Traditionally, we have used cover crops for two main purposes: erosion control and additional spring forage. Today, however, the uses and benefits of the various grass and legume species is varied and numerous. Cover crops add organic matter to the soil enhancing the natural productivity and fertility of our soils, they help to scavenge and hold nutrients which are then available to the following crop, and they are an essential tool in successful no-till production systems.
Species selection and use is an exciting area of farmer interest and industry research. New and less commonly used species do however come with some risk and tend to be more difficult to manage than good „ol rye or another cereal grain. Species which are now becoming more common within the capital region are: crimson clover, hairy vetch, annual ryegrass, forage radish and other brassica species. Much of the interest in non-legume species is for the purpose of trapping and holding nutrients, such as from fall and early spring manure applications. While legumes, such as crimson clover and hairy vetch, will be able to capture 70-150 lbs of nitrogen and then release it for the following crop. In my mind a legume would be the most useful in situations with no manure or limited and uneven manure use. In essence you are growing your own nitrogen fertilizer.
One rule of thumb to remember for all cover crops is that the amount of top growth present in the spring is proportional to the amount of nutrients contained within the roots and the entire plant. Its common sense but very important to consider. As the cover crops decompose they will release much of these nutrients back into the soil-It‟s what my grandpa called “green manure”. This is especially true of the nitrogen in legumes. It‟s true in grasses as well; however, if your grass‟s top growth has started shooting heads or becomes “stemy” and lignified, a portion of the N and other nutrients will be tied up in the fodder and not available to the next crop. As stated above, more biomass generally means more nutrients and organic matter returned to the soil, to obtain greater N benefits you will want to consider delaying legume termination and corn planting until early May. Cover crops burned down in April have significantly less biomass. This is especially true of legume species (see table at right for average dry matter production in the last 5 years*)
Keep in mind that grasses can be seeded late into the season, often up through the end of October, but legumes should be started in late August until no later than the end of September (the 20th is preferred). If planted to early the following can smother if they become to rank: hairy vetch, crimson clover and even annual ryegrass. They also will not establish well or have very little fall growth if seeded too late in the season. A little manure applied pre or post planting will help these three cover crops establish quickly, however avoid heavy manure applications which can stimulate excessive growth and can worsen winter kill. I would also consider adding a small amount of a nurse crop such as triticale, ryegrass or wheat (rye will head too early) if planting a legume. A bushel or less should bring you the added benefits of a grass species without being too competitive with the legume.
From fall establishment to spring termination, I cannot begin to cover all the issues associated with successful cover crop use. So, let me leave you with some questions about your situation.
- What is your primary goal/need? forage, N from a legume, nutrient scavenging, soil building, erosion control
- What are you constraints? planting date, harvest date, equipment
The Penn State Agronomy Guide and other resources are available to you. Use them to avoid disappointing results when developing new cropping systems. Whether to improve your no-till success, grow more N for your corn, or build up your soils with living roots year round, cover crops are playing an increasingly important part in crop production in the Capital region.
*Vetch did not establish well in two seasons and therefore has a lower than expected yield.