Cover Crops for Fall Planting
August is a great time to plant cover crops. There are so many to choose from. However, as summer winds down and we move into September, the options for cover crops start to shrink a bit. Basically you need at least 6 weeks of good growing weather (for that particular cover crop) to really justify the cost for many cover crops. When choosing a cover crop for fall planting, consider your goals - do you want erosion protection over the winter or to grow some nitrogen for next years crop or just to build some soil biodiversity and extend the biological activity a little longer in the fall. Another consideration - terminating the cover crop - will it die over winter or will you need to use tillage to control spring growth?
Erosion protection - fast growing grasses like oats, barley, rye, triticale and wheat are good options for quick ground cover in the fall. The fine, fibrous root systems will help to build soil structure while protecting the soil surface. Choose oats, barley or the spring varieties of wheat and triticale if you need the cover crop to die before spring.
Grow some nitrogen - clovers like Crimson clover are an option, if planted in August. This is a relatively fast growing clover that is inconsistent in overwintering. Another option is peas. Ontario research has shown that there is little nitrogen transfer to the succeeding crop in conventional systems from pea cover crops. However, peas planted in August and September can put on some good growth under the right conditions and when combined with a grass, can make a useful green manure crop or if necessary emergency feed.
Building biodiversity - cover crops do more than just cover the ground, the roots and the root exudates provide food and habitat for a multitude of soil organisms. Planting a cover crop mixture can assist by creating more diversity, creating a "more natural cover". The thought is that multiple cover crop species will have more resilience. The cover crop will recover or respond better to stress and be more productive across the variability of a field. There has been some suggestion from research in the US Midwest that mixtures of 6 or more species are optimal. Many of these mixtures are based upon the concept of warm season versus cool season and grasses/legumes and other broadleaves to create mixtures of four or more species.
You will notice that oilseed radish has not been included in the suggestions above. This "rock star" of the cover crop world has a number of roles where it is an excellent cover crop choice, however limited growth potential after early September make it less suitable, except as part of a cover crop mixture.
To help you make cover crop decisions for this fall - check out the new Cover Crop Decision Tool for Ontario - on the Midwest Cover Crop Council website at http://www.mccc.msu.edu/selectorINTRO.html.
Figure 1: Fall growth of Crimson clover planted after wheat harvest 2011
Figure 2: Six years of constant cover cropping with intensive cash cropping/livestock has built soil structure and supported soil life.
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