In the not-too-distant past, it used to be that farmers gave their straw away for free. That is no longer the case.
John Heard, of Manitoba Agriculture, Food, and Rural Initiatives (MAFRI), has been doing soil fertility extension work in Manitoba for about 16 years.
These days, Heard said, “There’s an appreciation that there are soil nutrients in straw — about a third of the phosphorous and a third of the nitrogen that the crop takes up, as well as much of the potassium. So a lot of the nutrients are there, although not in a water soluble form, generally released upon the straw’s microbial breakdown.”
According to Heard, straw’s nutritional value varies. “Environmental and growing conditions determine grain yield and how well nutrients are mobilized from stalk to grain. Soil fertility level and applied nutrients have a major impact on straw nutrient content.
“From crop harvest, nutrient export derived would be comprised of about two thirds to 80 per cent nitrogen and phosphorous and maybe 20 per cent potassium from the grain.
“Potassium from the straw is fairly water soluble.” Heard says it will wash out readily, replenishing soil reserves. But nitrogen and phosphorous need moisture and warmth to allow the necessary microbial breakdown.”
“Estimating the straw’s nutrient release is tricky,” Heard says. “It’s dependent on the carbon-to-nitrogen ratio, temperature, moisture, and microbes. When straw has a high C-to-N ratio, straw removal or burning may increase short term N and S availability.”
Heard says removing straw removes the food supply for soil microorganisms. This slows their growth, decreasing their demand for nitrogen and resulting in less immobilized nitrogen.
“Farmers have learned how to manage this,” Heard says, by “working in some nitrogen by banding it and placing it beneath the residue — the zero till idea.
“When physically separated from the residue, it can be quite efficient — feeding the crop before it feeds the bugs to break down the straw.”
Nuisance or nutrients
Some farmers reap more income from selling bales than the straw’s fertility value, but Heard suggested, “There should be pretty good financial enticement to part with your straw.
“Some farmers may consider straw a nuisance if they don’t have the machinery to chop, spread, and work it into the soil.” These farmers are more likely to sell their straw for a profit.
Other farmers want to sell the straw to get it out of the way. While there is fertility there, Heard says, “it’s slow release, not occurring until the following season. Sometimes not early enough for quick growing crops like canola and cereals.
“It’s increasingly difficult to assign values to other benefits of straw, such as maintenance of soil organic matter levels, improved soil structure (including water holding capacity and infiltration), and erosion control,” Heard says.
There are also other benefits association with leaving straw in the field. These include replenishing organic matter and cover, which reduces evaporation, as well its microbial breakdown which helps encourage soil structure.”
Even when straw is harvested, Heard says much of it remains in the field. “The density of the straw from the base of the plant that isn’t harvested is greater than the density of the straw above it — and all that growth is returned.
“Many studies on Prairie black soil tend to show we don’t have much soil degradation, as the initial organic processes levels are high and we still return good residue even in the stubble.
“Farmers who are more leery about exporting straw are those on sandy soil (low in potassium), as potassium is the highest nutrient left in straw. And potassium is three times the price it was 10 years ago and is an expensive nutrient to replenish.
“We don’t need much potassium on our clay soils, but we certainly need it on sandy soils. And if people are harvesting and moving their straw from the soil, potassium is what they’ll end up needing to buy from fertilizer companies.
If you sell your straw, Heard says, buy fertilizer to make up the difference. Or, he suggests, “even better is to sell your straw to the local livestock producer and then get back the manure application for your land.”
Choosing not to bale
Larry and Pat Pollock are organic farmers approaching semi-retirement. Their 600 acre farm is northeast of Brandon, where they grow ancient grains and alfalfa hay.
“As organic farmers, we choose to not bale crop residue,” said Pat. “We want to return as much organic material to the ground where it was grown (in place/sheet composting).
“The NPK and trace minerals stay right in the field and are slowly released to future crops. The crop residue in straw particles improves the soil texture, increases the soil’s organic matter, and allows better root zone aeration.
“The layer of chopped straw acts as mulch to reduce wind erosion of the valuable topsoil and improves moisture retention. Moisture stress in plants increases their susceptibility to disease.
“The soil’s improved ability to absorb water decreases the leaching potential, especially in sandy soils. The presence of added straw helps to break up clay particles and to loosen the root zone. The mulch layer helps to regulate soil temperatures and will reduce the heaving that occurs during freeze-thaw cycles.
Not baling leaves the Pollacks with fewer trips over the field, and less soil compaction. This frees up their time and saves them from buying bales and trailers.
But if you do decide to bale, make sure to make up for the lost nutrients. “Farmers following soil tests will step up their application rates accordingly,” Heard says. “If they’re getting paid for straw, they can use some of those funds to pay for that.” †