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Some old ways aren’t better, but…

Long-term rotation study underlines that summerfallow harms soil health, but the old mixed farming model looks pretty good

You might think that a long-term crop test might mean five years. A decade would be remarkable. But what could plots tell you about soil health if they’ve been going on for 87 years?

They would tell you that Prairie farmers were right to stop keeping fields in fallow as part of a rotation and instead move to minimal or zero tillage. They would also make clear that the use of manure and perennial forages in the rotation can have significant positive impacts on long-term soil organic matter and crop yield.

The Breton Plots tell that story, and although the specific crops grown for the last 87 years in the same set of rotations may not be the most favoured crops or rotations today, the wisdom of the soils continues to be read by researchers at the University of Alberta.

The Breton Classical Plots were established in 1930, just east of the town of Breton and 100 km southwest of Edmonton. The Hendrigan Plots, a second set of long-term plots at the same site, were established in 1980. The soils are Gray Luvisolic soils that developed under boreal forest, unlike most of the farmland in the Prairies that developed under grassland and is known as brown or black soils. The boreal forest-influenced soils were challenging to manage due to low organic matter after the forests were cleared.

Still, Miles Dyck, an associate professor in the department of renewable resources at the University of Alberta, says the long-term plot results should be transferable to most other soil types.

“In terms of processes that occur in soils, they are generally not dependent on soil type, such as nutrient cycling and organic matter buildup,” he says. “Why we see such dramatic differences there, is the soils were so low in organic matter to begin with. They tell a good story.”

Figure 1. Soil organic matter percentage as affected by crop rotation and nutrient treatment, 2013 soil sample analysis results. Error bars represent the standard error.

In the days of wheat and fallow

The story starts in 1930 with low organic matter soils and Prairie cropping practices in which wheat was the star. Fallow was also used regularly, but mixed farming was also practised with regular forages in the rotation. The researchers wanted to reflect both of those systems and as a result two major crop rotations have been studied for almost 90 years since: wheat-fallow and wheat-oat-barley-hay-hay.

“Superimposed over the two rotations are eight different fertility treatments,” says Dyck. There’s a check with no fertilization and the rest have a combination of chemical fertilization and manure.

“It’s really designed to help farmers figure out what kind of crop rotation and fertilization and nutrient management are best practices,” Dyck explains.

The Hendrigan plots established in 1980 by soil science professor Bill McGill look at three different rotations, including continuous grain with chemical fertilizers and other systems with longer-term rotations with legumes and forages so that all the nutrients are supplied through legumes or manure.

The trials allow researchers to read what professor emeritus Jim Robertson calls a “library of information” from the soils.

“The soil stores information on the long-term impact of these systems,” says Dyck. “What’s emerging is rotations with more diversity, including cereals, legumes and forages are better in terms of soil health.”

Figure 2. The effect of crop rotation and nutrient treatment on average wheat crop yields in each rotation, over a-nine year period (2007 through 2015). Error bars represent the standard error.

Plots in the wheat-fallow rotation with no fertilizer or manure have seen a 24 per cent loss in soil organic matter to 1.8 per cent. Plots with chemical fertilization with nitrogen, phosphorus, potassium and sulphur have less loss in soil organic matter, but it has dropped to 2.2 per cent in that treatment. Manure application has significantly improved soil organic matter, increasing it to 3.6 per cent.

Dyck cautions that the applied manure has been composted and at a level to supply all of the nitrogen needs of the crop, which would be at a fairly high volume. Manure increases the tilth of the soil, along with providing nutrients.

“Not everyone is in a position to apply manure. Shipping costs can be prohibitive. We’ve also seen in the five-year and eight-year rotations that including perennial forages as part of the rotation are an excellent way to increase organic matter.”

The trend towards cover crops could also help increase organic matter.

“Farmers are interested in (cover crops) and researchers are looking at them as well. Anything you can do to increase biomass additions to the soil is a good thing,” says Dyck.

The Breton Plots are overseen by a management team and are funded between 50 and 60 per cent by an endowment. Dyck says he hopes that the endowment can someday fund 100 per cent.

With no canola in the rotation, it could be argued that the plots need to change, but there are no plans to do so. Where else can you find almost 90 years of consistent plot treatment?

The researchers have, however, adapted the varieties of crops in the rotation to reflect modern usage, and fertility treatments have also been updated.

The Breton site was originally 20 acres on land farmed by Ben Flesher. Ben’s son Bill and his wife Sylvia recently sold another 60 acres adjoining the original plots at a fraction of market price so that the land can also be used for research plots. That research will contain new plot research to be conducted by Miles’ colleague Guillermo Hernandez Ramirez, looking at perennial cereals.

About the author

Field editor

John Greig is a field editor for Glacier FarmMedia.

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