Flax crop residues can be a costly nuisance for Saskatchewan growers if they aren’t managed carefully. They wrap around seeding equipment in the spring, increase downtime in the fields, and interfere with seed germination, taking a chunk out of the bottom line.
According to Dr. Jeff Schoenau (Professor of Soil Science at the University of Saskatchewan), harvest conditions could influence decisions surrounding residue management strategies.
“Flax tends to be harvested last in later fall when it is cold and damp,” said Schoenau. “This allows the straw to become tough which makes it chop poorly”. This can make it a real tangly issue come seeding time.
Saskatchewan growers may turn to vertical tillage, discing, or burning as strategies for handling flax residues. While each of these options are effective at reducing the amount of straw and stubble left in the fields, are they always worth the effort?
To answer this question, Dr. Schoenau teamed up with colleague and soil physics professor Dr. Bing Si to conduct a large-scale research trial, funded through the Saskatchewan Wheat Development Commission, the Saskatchewan Pulse Growers, the Western Grains Research Foundation, and the Saskatchewan Ministry of Agriculture through the Agriculture Development Fund.
“We were interested in learning how these different residue management strategies would affect the condition of the soil and the crop yields in the following growing seasons,” said Schoenau.
The three-year project began in the fall of 2015 near Central Butte, Saskatchewan. Each test plot spanned nearly five acres and contained residue from a recently harvested flax crop. The research team managed the residues on each plot using either vertical tillage, tandem discing, raking and burning, or no-till practices. Come spring, each plot was seeded to red spring wheat, while the subsequent two years were seeded to peas and then to canola.
The research team evaluated each of the long-term effects of their flax residue management strategies based on soil health and structure, crop yields, and cost of production.
“The first thing we measured was the effect of flax residue management practices on soil water infiltration over three crop years,” said Si, adding that, “In Saskatchewan, water is a major limiting factor for crop production.”
Flax stubble burning didn’t appear to have a major impact, but tilling reduced the soil’s moisture content compared to untilled plots.
“That is what we expected,” said Schoenau. “Tillage tends to dry out the soil, because if you get rid of that stubble on the surface you don’t have as much snow trap during winter.”
During the first year of the study, they found that vertical tillage reduced air permeability of the soils compared to the other treatments. According to Schoenau, “We looked at this because the roots need oxygen and so do the microorganisms. We need aeration to allow the microorganisms to do their job like fix nitrogen.”
The researchers believe these findings might be explained by their use of rolling baskets behind the vertical tillage equipment which may have increased the number of fine pores in the surface soils.
Aggregate size and stability was another important consideration as predictors for soil erosion.
“We found that aggregate size wasn’t affected much,” said Schoenau, “but the tillage and burning practices did tend to decrease aggregate stability.”
Fortunately, the negative impacts of their tillage treatments appear to be short lived. According to Si, “The negative effects of tillage seem to disappear after a couple of years, so it doesn’t hurt as long as you don’t do it every year.”
The same couldn’t be said for burning, especially when considering soil fertility.
“Burning did show a small increase in phosphorus availability the following crop year, but you also lose carbon and nitrogen from the soil which can hurt in the long-run,” said Schoenau. “You may get a bit of short-term gain, but you potentially get some long-term pain from continued burning.”
When it came to crop yields. Schoenau and Si didn’t see any changes in crop yields the following three years after their residue management treatments.
So, what does all this mean for a producer’s bottom-line?
“If there is truly no difference in yield, but there are additional operation costs, it actually doesn’t pay,” said Schoenau.
Schoenau goes on to say, “If you’re able to harvest the flax early on when it’s warm and the straw chops well, you might not need to burn or till. Seeding directly in well-chopped flax stubble worked well, in our study.”
But when harvest conditions are not ideal, Schoenau and Si agree that periodic use of tillage practices are a viable solution to handling difficult crop residues.
“Vertical tillage doesn’t hurt the soil if you don’t do it every year,” said Si. “If the purpose is for residue management and weed control in problem spots then you can do it and the effects will dissipate over time.”
Ultimately, a successful residue management program all comes down to optimizing harvest conditions and paying attention to the needs of the land.
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