MANITOBA CO-OPERATOR — Manitoba dry bean growers could one day cut nitrogen fertilizer rates nearly in half without sacrificing yield, according to new research from the University of Manitoba.
Speaking at a July 29 field day in Carman, university research agronomist Kristen MacMillan said she’s in the final year of a study examining how much nitrogen dry beans can fix from the atmosphere through nodulation and whether lower fertilizer rates could be viable for Prairie conditions.
“We’re still waiting for the final results of this study, but almost 50 per cent reduction in the nitrogen rate would have really important economic benefits for farmers,” said MacMillan.
That finding could come at an ideal time. Manitoba farmers planted a record 207,000 acres of dry beans in 2025 — including a record-high 123,000 acres of pintos — the highest dry bean acreage in two decades.
Dry beans are in the same legume family as peas and soybeans, well known for fixing their own nitrogen out of the atmosphere. Dry beans, though, are worse at it.
“The main reason is that it’s non-selective as a host, so it’s fairly promiscuous with the rhizobia in the soil, and that reduces its efficiency in fixing nitrogen,” said MacMillan.
That reputation has led to full fertilizer programs as standard practice. But MacMillan’s current trials aim to test whether modern cultivars — grown in Manitoba soils that have seen decades of pulse production — might be capable of fixing more nitrogen than previously thought.
Two earlier studies that MacMillan worked on — including nitrogen rate trials completed in 2022 at Carman, Portage la Prairie and Melita — showed that dry beans did respond to fertilizer, but not at economically optimal levels. MacMillan’s earlier work also looked at inoculants, which varied by product.
A summary of dry bean nitrogen and nodulation on-farm trials from the Manitoba Pulse and Soybean growers, which cites MacMillan as one contributor, said that yield increased in small plot pinto and navy beans (located at Carman and Portage la Prairie from 2017-2019) at high nitrogen rates of 140 pounds per acre. “When considering the return on investment, it was statistically the same for all rates of N application, meaning the economic optimum rate was to not apply any N fertilizer at all,” the summary noted.
It also cited black and pinto bean trials at Brandon, Melita and Carberry from 2021-2022, which found no yield change with different fertilizer rates, with the exception of uninoculated black beans in Melita in 2022.
The same resource noted that fertilizer had an inverse relationship with nodulation. The more fertilizer they put on, the less nodulation they saw.
Plants “become ‘lazy’ and rely on soil nitrogen alone,” the grower group said.
Measuring nodulation
MacMillan’s team has rated nodulation. Until now though, it wasn’t clear how much nitrogen those nodules were actually providing.
That’s the focus of her current research: how much atmospheric nitrogen dry beans are fixing under Manitoba conditions, and whether that amount changes depending on nitrogen rate and inoculation.
One set of plots at the University of Manitoba’s Ian N. Morrison Research Farm is measuring nitrogen fixation across 12 popular dry bean cultivars using a method called “natural abundance,” which tracks nitrogen isotopes. A second trial is testing nitrogen fixation under different fertilizer rates, with or without inoculant.
“The hypothesis that’s being tested is whether we can move from a full rate of N fertilizer down to a low rate and still maximize yield,” she said.
Dry beans in Manitoba typically yield around 2,000 pounds per acre, which translates to about 90 pounds of nitrogen. MacMillan said literature suggests N fixation could provide up to 20 to 40 per cent of that requirement — a meaningful contribution, especially when combined with residual nitrogen already in the soil.
In addition to saving farmers money, the less nitrogen applied also means less nitrous oxide, a powerful greenhouse gas, is released into the atmosphere.
“Environmentally, this could lead to less nitrogen-intensive cropping systems when it comes to growing dry beans,” she said.
About the author
Associate Editor, Grainews
Don Norman is an agricultural journalist based in Winnipeg and associate editor with Grainews. He began writing for the Manitoba Co-operator as a freelancer in 2018 and joined the editorial staff in 2022. Don brings more than 25 years of journalism experience, including nearly two decades as the owner and publisher of community newspapers in rural Manitoba and as senior editor at the trade publishing company Naylor Publications. Don holds a bachelor’s degree in International Development from the University of Winnipeg. He specializes in translating complex agricultural science and policy into clear, accessible reporting for Canadian farmers. His work regularly appears in Glacier FarmMedia publications.
Related Coverage
Ramp up your nitrogen efficiency in winter cereals: VIDEO
On-farm research translates crop breakthroughs into ‘farmer speak’
Federal money to grow Manitoba agriculture manufacturers
VIDEO: Yield-eating weeds and pest insects tackled at field day
Soil moisture, more timely application may help limit fall fertilizer loss
