USA
August 29, 2024
As every grower knows, the two concerns in oilseed storage are spoilage and insect infestation. Both can be controlled by managing the delicate balance between a stored crop’s temperature and moisture.
TEMPERATURE + MOISTURE EQUATION
To manage insects, colder is better: most storage insects go dormant around 50°F and are killed outright if grain can be held below freezing for a period of time. To manage spoilage in either oilseed sunflowers or canola, the industry’s typical recommendation is 8% moisture and a maximum temperature of 60°F. Just how much does temperature matter to safe storage length? A whole lot.
“Stored canola at 12% moisture and 60°F, all you’ve got is 18 days before there’s enough spoilage occurring that canola starts clumping together. Farmers might call it sweating, but it’s spoilage,” says Ken Hellevang, North Dakota State University Ag Engineer and a grain drying specialist. “If you can cool that same 12% moisture canola to 40°F, now you’ve got about 110 days. It all hinges on temperature.”
Moisture matters too. At 10.6% moisture, Hellevang says stored canola should be safe for 40 days at 60°F and 238 days at 40°F. Add just 1.4% more moisture and the safe storage length drops by more than half.
As plant breeders continue to improve oil content in oilseeds, producers may need to take a hard look at whether the 8% moisture level traditionally accepted as ‘safe’ for longterm oilseed storage is, in fact, still safe.
“Historically for canola and sunflower, we could probably get by with 8% as the recommended moisture content,” says Hellevang. “As oil contents of both commodities increase – we’re seeing oil contents for sunflowers increasing up to about 45% — the moisture content that’s safe for storage is reduced. Typically, today we’re talking about 7% moisture being safe for summer storage, where it just didn’t have to be that dry when guys were storing it 30-40 years ago.”
MANAGING THE CORE
Oilseeds are at highest risk of spoilage in the central core of a grain bin. Two key factors typically contribute. The first, in any crop but particularly in the case of sunflowers, relates to dockage. When relatively large sunflower seeds flow into a bin, particles segregate depending on size and density, explains Hellevang.
“We end up with a spout line or an accumulation right under the center of the fill hole that is typically much smaller particles, whether that’s weed seeds or broken kernels. Because it’s more difficult to get air flow through that finer material and it tends to be higher in moisture content, that tends to become an area where we have more storage problems.”
The second factor relates to temperature differentials. The riskiest period for oilseed spoilage tends to be the two- to four-week window after harvesting if a grower doesn’t run air right away, and again post-winter when the difference between the temperature inside the bin and the warming temperatures outside the bin create convection currents through the grain.
“Especially in spring if you get warm air going up the sides of the bin, going over the top and coming down through the center, that will increase the grain temperature and moisture, which can spoil the grain in the top center of the grain,” says Barry Coleman, Executive Director of the Northern Canola Growers Association.
While that kind of convection current can be problematic in any storage bin, canola is particularly at risk, he adds. “The small seeds and high oil content means it’s very tough to move air through canola, so getting the temperature down is the main thing and cooling is more of a priority than drying.”
Most producers’ go-to solution for managing convection current induced heating in the center of the storage is known as ‘coring the bin’ (unloading grain, which will ‘take the top off the bin’). Coleman says pulling canola from the crown of the storage down through the middle of the bin, and then either shipping it or moving it to a secondary storage, is a very effective way of managing heating in the middle of the bin. Successful storage managers use coring the bin as just one option in a whole suite of proactive management tools, all underpinned by careful, consistent, on-going monitoring.
“I’ve got a slide in the storage presentation I do for producers that says: ‘Management means making decisions based on understanding the science of grain storage.’ If we’re going to manage the storage, we need to make sure that we’re monitoring all its different aspects. Having cables in place does not eliminate the need for people still looking and smelling and using some of those old technologies like putting samples into a moisture meter,” Hellevang says.
Bin Monitory Technology Options
Today’s bin monitoring technology puts your stored crop’s status right in the palm of your hand, with real-time updates easily viewable on any smart device. That said, producers need to understand both the value and the limitations of bin monitoring technologies.
TEMPERATURE CABLES
Temperature cables are a smart management strategy that should be installed in every bin, says Ken Hellevang, North Dakota State University Ag Engineer and a grain drying specialist. However, producers need to recognize that they provide temperature spot checks, not a comprehensive picture. “If you look at most grains, they have an R [insulation] value of about 1/inch. So, if heating is happening two feet away from that temperature sensor, that’s an R24 insulation barrier between whatever’s happening and the cable. That’s more insulation than you’ve probably got in your house.”
In fact, he points out, researchers at Purdue University put full gunnysacks of wet grain into bins about three feet from temperature cables to test the cables’ sensitivity in an extreme heating situation. Despite the grain in the sacks intensively rotting, the temperature cables were unable to pick up on the heating. “A temperature cable tells an important part of the story, but it’s just part of the story,” says Hellevang. “Guys tend to rely on them too much.”
MOISTURE SENSORS
A more recent addition to the grain monitoring world is moisture sensors. Moisture sensors measure air temperature and the air’s relative humidity which, when combined in a formula, should produce a reasonably correct moisture content reading. That’s not quite the case, however.
“The unfortunate thing is the relative humidity measurement is not really accurate. If you look at the literature, it’ll usually say that it’s measuring the moisture content to within plus or minus one percentage point.” Sunflower measuring 10% moisture could actually be 9% or 11%: a variation that could drastically impact the stored
crop’s safety.
CO2 SENSORS
The newest monitoring technology measures carbon dioxide levels — a by-product of both insect activity and spoilage — in storage. According to research from Purdue, it is possible to detect spoilage more quickly using CO2 measurements than any of the other methods. That said, more work is still required before the technology can meaningfully contribute to storage safety, says Hellevang.
“It’s so new that I’m not sure that we totally understand its practical application. Where do you put your sensors? How important is making sure that the fan is off? How important is having a seal versus letting the wind blow through?”
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