A cover crop trial conducted at the Ridgetown campus of the University of Guelph suggests that the economic benefits of growing cover crops is equal to or better than the results of its no-cover trials after factoring in the cost of seed and other inputs for the cover crop.
While in most cases there was a yield response, Dr. Laura Van Eerd, lead researcher on the project, suggests that the real benefit of growing cover crops may be more long term by way of increased organic matter and soil tilth.
"If you're going to see an effect from cover crops it won't be from planting them in one year," Van Eerd says.
"It's not as clear cut as I would like to see it. Sometimes we're getting a yield boost and other times we don't, but the economic results come out better.
"However, that is a short-term view and if one looks at it over 10 or 20 years, the benefits may be significant.
"We are trying to look at year-after-year and the real benefit will be from adding carbon and tilth to the soil."
Van Eerd noted that an OMAFRA economist crunched the numbers on the project and factored in the cost of cover crop seed, herbicides, and custom application of herbicides in calculating the return.
The project examined trials on a number of different cover crops and their impact on several crops such as seed and sweet corn, tomatoes and cucumbers.
"What he found was that compared to the no-cover plot, cover crops resulted in crops the following year that were more profitable or just as profitable as the no-cover trial," Van Eerd says, adding that, based on added crop profitability, there was no net cost to growing the cover crop.
"There was a yield increase in most cases and most times it was significant, but not always."
She notes that 2010 was the third year the project has used cover crops before and after harvesting cucumbers, and in most cases there was an economic benefit from the use of cover crops.
"We have cover crops with no nitrogen added and cover crops with nitrogen applied and they all are all yielding about the same in economic terms," she says, noting that because cucumbers are marketed at different values based on grade the economic impact was measured rather than on straight yield increase.
"I'm not saying you should grow cucumbers without a nitrogen application and just plant a cover crop, but if we were comparing apples to apples, the no-cover crop with no nitrogen would yield better if a cover crop were added."
Van Eerd notes that in terms of dollars-per-hectare benefit, the trial plots ranked oilseed radish as the best, then oats, vetch, peas, no cover crop, and then rye.
"Because rye over-winters we've found that slugs can be an issue so you want to be aware of that," she says, adding that the lush green tissue of the rye in spring acts as a magnet for slugs.
"If you grow a rye cover crop I would recommend that you kill it or incorporate it early in the spring."
Van Eerd says if rye is left to grow in spring it can also draw down the soil's nitrogen levels, which may account for the decreased yields found in cucumber crops following the rye treatment.
She adds that in terms of dollar return on early and late plantings of cover crops there was no difference in the cucumber crop, and she found that surprising when considering the difference in the growth of the cover crop.
"We're trying to figure out why and I don't have an answer right now but possibly it's because the cover crop is contributing to the soil's tilth," she says.
"But from a practical point of view I would say plant early. Typically we like to get our cover crops in by mid-September. If it's later than that we are questioning whether we are getting enough biomass. But if you are planting late, I prefer oilseed radish because it grows quickly."
Van Eerd says the question that must be asked is: Is the economic boost derived the following year from an increase in nitrogen, or is it from improved soil tilth?
"We're not seeing a huge nitrogen credit, but if it were just nitrogen you would expect the cucumbers to be higher yielding in terms of tonnes per hectare, but that's not really the case; they are about the same.
"So I think it has a lot to do with improved soil tilth."
Van Eerd points out that the trials have been conducted on exceptionally good vegetable-growing soil.
"It's excellent land with good fertility, nice texture and tilth," she says, adding that improved soil quality resulting from cover crops may be more significant on poorer land.
"This is great vegetable land and cover crops are making a difference, so I would encourage growers to go to their worst land and see how much difference they can make there."
Van Eerd says she would not have suggested that when she started the project four years ago.
"We've been repeating this and now I am starting to think, wow, in vegetable production it's a winner and if we can get these differences maybe we can see bigger improvements on poorer land."