By John Greig
One of the biggest challenges for organic farmers is coming up with the complex crop rotations that help them manage nutrients, markets and environmental impacts.
Katherine Stanley, a research associate at the University of Manitoba, outlined the multiple factors organic farmers need to take into consideration when determining their crop rotations at the Guelph Organic Conference.
The University of Manitoba has the longest experience with organic rotations with their plot at the Glenlea Research Station that’s been in organic production for 25 years. They also have organic plots at Carman, Man.
Stanley outlined five major factors that should go into crop rotation decision. Many of them are big picture.
- Is the crop rotation vulnerable to fluctuating market demand? Stanley has done some consulting with a 10,000 acre organic farm in the Ukraine. They were so excited by the price of organic spelt that they put half of their acreage into the crop. So did every other organic producer and by the time harvest came around, the price of spelt was definitely unexciting.
- Soil building: making sure to alternate nitrogen fixers and consumers. Take a look at which crops are more profitable cash crops and which cover crops need to be grown in order to enhance soil and nutrients. Make sure they complement each other.
- Conserving nutrients: making sure to know the nutrient demands of crops in rotation. This is where it’s important to check out manure application in order to supplement cover crop-delivered nutrients. The University of Manitoba decided that it needed to add manure to its crops in its long-term rotations.
- Build soil fertility through the creation of biomass. This includes cover crops and where you consider how to manage weeds and pests through crop rotation. It could also be green manure built into the rotation, as is common in Western Canada.
- Demands on labour and equipment. A farmer may have to make changes in the rotation if he doesn’t have the employees or equipment needed to plant or harvest the crop.
Organic farmers need longer-term planning in order to avoid problems with their rotation. It goes beyond thinking about the corn-soybeans-wheat rotation of conventional farmers.
At the Carman research site, lead researcher Martin Entz, Stanley and their associates have a six-year rotation:
- Green manure;
- A grain legume (now often soybeans);
- Green manure;
- Oat/rye mixture
They also put about 7.8 tonnes of manure per acre on the plots over the six years. Growing a green manure every three years provides enough nitrogen for the rotation. An initial rotation at Glenlea had a green manure every four years, but it was running short of N and a decision was made to move up the rotation by a year.
“At Glenlea, we didn’t include manure for the first 10 years,” she said.
She pushed Ontario organic farmers to think about the sustainability of the common corn-soy-wheat, then red clover rotation.
“There are a lot of heavy nitrogen feeders in this rotation. I’m not sure we have enough nitrogen in this rotation,” she said.
At the University of Manitoba, researchers are working on on-farm nutrient budgets that examine what level of nutrients are used and exported off the farm, looking rotation and crop yields.
That way a farmer will know if there’s a net loss of nitrogen per acre over the entire rotation.
There are more cover crops in use than ever before and it can be challenging to figure out which to use.
Stanley suggests checking out the Prairie Organic Grains Initiative (POGI) where they have put together resources including a long list of cover crops and information about when to grow them.
The list can be found at pivotandgrow.com.