Originally published November 14, 2019 on The Western Producer
By Robert Arnason
If you feed the micro-organisms in the soil, they will feed us.
Many soil experts believe a healthy population of soil bacteria is critical for a healthy and productive soil. If farmers reduce tillage, grow cover crops and minimize the use of chemicals, the soil micro-organisms will thrive.
A Montana State University study, published in October, indicates it’s not that simple. Other factors, like temperature and moisture, are much more important for soil micro-organisms.
Montana State scientists found that the population and diversity of soil bacteria peaks in June, drops off in July and is highly dependent on moisture.
“There is a big seasonal effect,” said Tim Seipel, a plant ecologist at Montana State, in Bozeman, Montana. “Just think of this fall. There’s not much biology going on out there. We’ve had a painfully cold and snowy fall (in Montana).”
Soil health is a hot topic in agriculture and so are beneficial soil bacteria. The bacteria help plants find nutrients in the soil, stimulate plant growth and possibly protect plant health.
Seipel and his colleagues took soil samples and assessed the bacterial diversity of soil around wheat roots. They took samples from three different production systems: no-till, organic and an organic system with reduced tillage — at the university’s Fort Ellis Research Center near Bozeman.
One of the things that strikes me is that processes are really slow here… Now I have an easily understood difference in soil health. – Tim Seipel
After analyzing the bacteria within the samples, the results were similar for no-till, organic and reduced tillage organic.
“Bacterial richness and evenness peaked in early June and dropped by late July, but was not different by farming systems,” the researchers wrote in a paper published in Geoderma.
“Seasonality may result in variations in temperature, precipitation, soil moisture, and solar radiation, all of which drive rates of soil microbial metabolism and respiration, as well as taxonomic composition.”
Bozeman is about 500 kilometres south of Medicine Hat, Alta., so spring and warm temperatures arrive earlier than in Western Canada. But the scientists found similar results in Havre, Mont., which is much closer to the Canadian border.
“The differences (between systems) are surprisingly small,” Seipel said.
He wasn’t shocked by the result, because the Northern Plains of North America have a cool and dry climate. Changes in soil health and soil composition happen slowly, so introducing cover crops or stopping tillage won’t have an immediate effect.
“One of the things that strikes me is that processes are really slow here,” Seipel said. “It isn’t as simple as ‘I did all these things’. Now I have an easily understood difference in soil health.”
The Montana State finding confirms what Marla Riekman, a Manitoba Agriculture soil expert, has said about soil health tests.
In a dry June, a soil health test will produce one number. In a wet June, the exact same test at the same location, will produce a completely different number.
“We need to understand those results can sometimes be affected by the seasonality. Or, might not be repeatable,” Riekman said in October, at a soil health conference near Winnipeg. “That’s where I’m at a loss…. I don’t how to make a recommendation from (the results) of some of these tests.”
The Montana study did produce a couple of surprising findings. For one, the researchers learned that weeds can alter the population of bacteria in the soil.
“Some weed species are better at recruiting beneficial microbiota than domesticated crops, allowing them to be more competitive,” the scientists wrote in their paper. “(It’s possible) that weed species are more dependent on plant-microbial connections, while crops only need them under non-ideal growing conditions.”
The researchers also learned that soil samples from zero tillage plots, had a higher population of soil bacteria later in the growing season.
“What we did see … is the tilled, organic system, the number of (beneficial bacteria) in there… did drop off more than in the no-till systems,” Seipel said. “Which, I thought, was interesting.”