Long-term cover crop research is moving beyond the basics to more complex interactions between covers and row crops.
Projects are now looking at how cover crops affect yield over several years, have an impact on crop quality and the value they could have if farmers get credit for reducing atmospheric carbon.
Why it matters: Economically justifying cover crops can be difficult, so more research is needed to further quantify downstream and long-term benefits.
Dr. Laura Van Eerd of the University of Guelph’s Ridgetown campus, heads what is now a 12-year set of trials exploring cover crops in rotations that include vegetables. She talked about her research at the Ontario Fruit and Vegetable Processors Association and the Ontario Processing Vegetable Growers conference recently in London.
With the benefits to the soil as a result of cover crops now firmly accepted, some of Van Eerd’s emerging aims include determining how cover crops influence crop yield and crop quality, and to what extent cover crop use would contribute to a farm’s offset to a carbon tax – if and when such a system is developed. And she believes her long-term project is well-placed to provide input for those determinations.
“We can’t expect changes in one year but we can, potentially, in a decade,” she said of the vegetable rotation trials in which she and her team have planted 161 cover crops over 12 years.
Only twice, she explained, have the results been significantly detrimental: once, a crop of rye got ahead of some cucumbers, but that was because of poor planting date on the cucumbers. And once, growing rye prior to spring wheat as a way of preparing ground for tomatoes, the rye also took over. That, she suggested, was simply proof that this rotation is unworkable.
In a trial testing three different cover crops followed by snap beans, there was a 10.6 per cent yield boost in the snap beans after oats compared to a control plot. “To me, that’s huge.” In another, sweet corn had a 6.9 per cent yield boost, on average, after a cover crop combining some permutation of oats, cereal rye, oil-seed radish, forage pea and hairy vetch.
Another trial showed no varying effect on yield in cucumber, snap bean or sweet corn from different planting dates of the cover crop. “For me, it means recommendations are pretty easy. Get a cover crop in when you can.”
One advantage of using cover crops in rotation with vegetable crops, Van Eerd added, is that the main crops are generally harvested early, meaning there’s a long cover crop growing season compared to a corn-soybean rotation. So the potential to build soil organic carbon is high.
As for the potential for cover crop-growing producers to qualify for carbon tax credits, “in my opinion, farmers should get compensated for their services.”
If such a system came into place, questions would be raised about how to factor in different soil types and cover crop varieties with respect to their potential to build carbon. But she’s confident trials like hers will be able to provide the information necessary for governments to accurately create a carbon credit system.