Cover Crops Cover All the Bases

by Gisela Duerr and Brenda Frick

The Organic Agriculture Centre of Canada is collaborating with the Jill Clapperton and Michael David at the Lethbridge Research Centre and Dean Spaner at the University of Alberta in a project to develop cover crop mixtures suitable for the Canadian prairies.

Cover crops are a valuable tool in cropping systems. Typically, cover crops are sown after other spring crops are in, and they are tilled into the soil before they set seed. They are a useful alternative to summer fallow, with the potential to return organic matter and nutrients to the soil while allowing for moisture recharge.

Different species have different characteristics that make them useful cover crops. Legumes and pulses host bacteria that fix nitrogen. Deep-rooted crops improve drainage and water infiltration in the soil. They also bring up nutrients from the subsoil. Crops with rapid growth can increase organic matter, prevent nutrient loss from the system, and suppress weeds. Crops that differ from the cash crops can disrupt pest and disease cycles.

Mixtures of different species have the potential to combine desirable characteristics, and to reduce the risks associated with their undesirable characteristics. For instance, an oat-pea mixture combines the nitrogen fixing benefit of a legume with the rapid growth of a cereal. The oat will support the pea vines, and reduce lodging.

The new cover crop study includes fifteen seed mixtures, and a total of eighteen different crops. Oat is a reliable, low-cost cover, with good ability to suppress weeds. Oat is tested with forage pea, faba bean, hairy vetch, woolypod vetch, crimson and Persian clover, lupin and chickling vetch. Faba bean and lupin are champions of nitrogen fixation when moisture is plentiful. Lupin grows a strong, deep taproot and acidifies the soil, increasing phosphorus availability. Chickling vetch is a legume with high water use efficiency which means it can produce a large amount of biomass under moisture stress. Hairy vetch improves soil tilth and helps cycle phosphorus. Woolypod vetch can produce abundant organic matter.

Sorghum-sudangrass is a fast growing warm-season plant with the potential to add large amounts of organic matter to the soil. It has an aggressive root system that can effectively break up hardpans in the subsoil. Sorghum-sudangrass is mixed with buckwheat and crotalaria (sunn hemp) or subclover (subterranean clover), and with cowpea. Crotalaria is a tropical legume that suppresses nematodes, resists drought and is associated with high levels of nitrogen fixation. Subclover is an excellent weed suppressor and a good nitrogen source. It is free of major diseases and relatively resistant to grasshopper damage. Cowpea is a heat-loving legume which tolerates drought and low soil fertility. Cowpea grows quickly in warm soils and attracts many beneficial insects.

The study also looks at three relatively unknown broadleaved species. Phacelia is an annual plant with a large, fibrous root system. It is a good soil conditioner and a great bee plant. Forage chicory is drought-resistant plant with a deep taproot. It can mobilize minerals from the subsoil. Phacelia and forage chicory are resistant to grasshoppers. Oilseed radish has a root system similar to chicory. In addition, it acidifies the soil and increases phosphorus availability.

Initially, this study will determine which of these crops do well under prairie conditions. Those crops that prove themselves will be studied further, to determine appropriate seeding rates, establishment methods and to optimize mixtures. We hope that this work will help increase the options that producers have to build and strengthen soil organically, and to maintain cropping potential.

Gisela Duerr, Ph.D., is a Research Associate of the Organic Agriculture Centre of Canada at the Lethbridge Research Centre, Agriculture and Agri-Food Canada. She can be contacted at 403-317-3375 or duerrg@agr.gc.ca. Brenda Frick, Ph.D., P.Ag., is the Prairie Coordinator for the Organic Agriculture Centre of Canada at the College of Agriculture, University of Saskatchewan. She welcomes your comments at 306-966-4975 or brenda.frick@usask.ca.


This article first appeared in The Western Producer, and is published here on the OACC website with permission.


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