Cover Crops – Quick Nuts and Bolts

Erin EagenJuly 2014

In recent years cover crops have become a hot topic at many of the major Ag conferences. What do we need to know about cover crops? Considering this option after wheat harvest, which cover crop is right for you? This article will give you a broad understanding on the benefits to cover crops and focus on three of the many options you have.

The first thing you need to ask when considering cover crops for your farm is what is your objective in planting a cover crop? Different cover crops provide different benefits. Both the cropping/tillage system you use and the amount of time you have for a cover crop to grow are critical in seeing positive results. Generally cover crops need 4-6 weeks of growth to equal the expense. An important aspect when choosing a type of cover crop is the location of the farm, along with the soil type and natural drainage of the soil. Some cover crops tolerate conditions with high amounts of moisture, whereas others can manage in drought conditions. These are all thing that one should consider when planting any sort of crop.

Advantages to growing a cover crop are numerous:

 Nitrogen Source – only legumes can fix atmospheric N into forms that are usable for plants. After you terminate a cover crop, much of the N will become available for the following cash crop. Once the termination of the legume has taken place, there should be N available in 1-2months.

 Nitrogen Scavenger – growing roots of a cover crop can absorb residual soil nitrates from fertilizer and soil organic matter mineralization. These scavengers will reduce the amount of nitrates that leach as well as protect water quality and helps build organic matter, thus potentially reducing the amount of N being applied in those fields.

 Soil Builder, Subsoiler, top soil loosener – cover crops at a very high level can improve soil quality, build organic matter and sequester carbon by adding roots and shoots to the soil. For example, fibrous root systems enmesh soil particles and provide food for micro-organisms. Deep roots can improve soil permeability which in turn increases the water filtration and aeration. Tap roots penetrate compaction in layers over time that gives way to macropores for future root growth.

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Erosion Preventer, Lasting Residue – is the most common use for a cover crop, protecting from wind and water erosion, as well the live root of the plants hold the soil together.

Weed Fighter – they have the ability to suppress weeds, creating competition, shade and potential allelopathy, (an organism produces one or more bio-chemicals that influence the growth, survival, and reproduction of other organisms).

Recycle Nutrients – nitrogen is generally the main focus of planting cover crops. However there are other nutrients that cover crops can tap into that are locked up in the subsoil by reducing soil erosion, building organic matter, and increasing soil biological activity.

Improve Water Quality – as said above cover crops improve water quality by decreasing erosion into drainage water.

Though there are many different forms of cover crops all with their one specific uses below.  We will focus on three.

Red Clover is used for either frost seeded/under seeded in cereal crop or inter-seeded in a standing crop. There are two types of red clover in Ontario; double cut “medium” red clover and single cut “mammoth” red clover.  The latter is slow growing, matures two weeks later than double cut and requires vernalization to flower. Single cut clover does not flower in the seeding year and is more drought tolerant.  (Vernalization is the ability to flower in spring by exposure to prolonged cold winter). Red clover should be planted shallow and a common suggestion is to inoculate rhizobium trifolii when planting. This type of clover can grow from 20-60cm in height; it grows best in moist, cool conditions and usually flowers within 65 days of planting. This cover crop has a thick tap root that grows 60-90cm per year; lateral roots are found mostly in the top 12cm of soil. This is done overwinter since it is considered a short lived perennial. It will grow on a wide variety of soil conditions, even soil which is slightly acidic pH.  For the best growth generally a pH level of 6-7 is desired. Red clover is shade tolerant and can persist 1-2 years in Southern Ontario and 2-3 years in Northern Ontario. Control for red clover is tillage and or systemic herbicide. This type of clover is sensitive to residual of atrazine and some Group 2. Red Clover is effective in weed control especial in under-seeding of cereal crops. As well as providing organic matter and nitrogen to the soil when tilled down.

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Oats are fast growing annual grass, more upright in growth habit and tillers less than barley. A full term crop can reach 1.3m, with fall growth reaching 20-50cm. The roots are fibrous and are not as aggressive like rye, only reaching 84-195 cm. This cover crop can tolerate a large soil pH range of 4.5 – 6.5, a pH range which is larger than both wheat and barley. It is sensitive to the triazine family, when effected this will reduce the growth of the crop. If there is a vigorous crop canopy it will suppress most weeds. A key point about oats and nitrogen is that it does not take up as much nitrogen as rye, though oats will winterkill and release nitrogen when it decomposes. If the oat stand is well established there is potential for a high quantity of biomass production. For erosion prevention, oats can be planted in a solid stand or wind strips alongside cool season vegetables like carrots for early wind damage and erosion reduction. Though they can be planted in wind strips, it is not recommended that this method be used in tomatoes or other vegetables, the height required for wind protection often is not established when controls must be applied.  If the conditions are too hot and dry a poor cover and a lack of erosion control may result.

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 Tillage Radish is similar to oilseed radish, however with slight differences. Oilseed flowers within 6 weeks and goes to seed if not controlled, becoming a problem weed the following spring. Unlike the oilseed radish, the tillage radish has a longer gestational period and will not flower in the same amount of time, making it a more viable option as a cover crop.  The benefits of tillage radish are rapid germination and growth and its ability to hold and release plant available nitrogen and other vital nutrients. It penetrates hardpan like a drill due to its taproot, decays rapidly and come spring the soil tends to be warmer and drier in some cases suppressing nematodes. It grows 50-100cm in height with a rapid top growth and the cover is complete. Radish is unaffected by early frost and resists mild freezing, though if temperatures reach -4oC the seedlings will die. Radishes will winterkill in normal winter conditions. This cover crop prefers cool, moist growing conditions, and thrives on well drained loams to clay loam soils; note the crop is highly intolerant of shade and or traffic. Tillage can be used to control radishes, wait for a good freeze and or use common burndown herbicides. Radishes have sensitivity to many Group 2 herbicides and triazine. For the best results when using tillage radish for weed control it is recommended to use a form of tillage as soon as possible after harvest and then seed into a stale seedbed. Do not delay seeding of the crop so as to create enough competition with weeds since there are no herbicides registered on radish. A downside of radishes is that decaying residue left on the surface overwinter can have a very strong odor. For planting radishes with a drill it is recommended to use 10 to 12lbs/ac and for broadcast use 12 to 15lbs/ac. The cost for the cover crop is moderate depending on variety, nematode suppressing varieties are usually higher in price.

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There is so much information on cover crops, below are some resources to help with choosing the best crop that suits your needs. If you are interested in more conversation on cover crops please contact you Veritas Agronomist.

Midwest Cover Crops – http://www.mccc.msu.edu/states/ontario.html

OMAF – http://www.omafra.gov.on.ca/english/crops/facts/cover_crops01/covercrops.htm

Cover Crop Solutions – http://www.covercropsolutions.com/