Temporary Storage of Sunflower Seed
Tuesday, September 1, 1998
filed under: Harvest/Storage
Will there be significantly more temporary storage of sunflower in 1998 than in prior years? This year's larger sunflower acreage and generally good crop conditions are helping round out such a scenario. The stage already has been set, as wheat and other small grains have filled countless farm bins and commercial elevators throughout sunflower regions due to low commodity prices and transportation bottlenecks. It appears the only place left for some sunflower crops will be inside pole barns or machinery sheds - or in outdoor piles.
Even though they're intended to be "temporary," such storages do require a degree of management in order to protect the sunflower seed from deterioration. Proper management becomes even more important if the days of temporary storage stretch out into weeks - and possibly even months, depending upon marketing considerations. North Dakota State University extension ag engineer Ken Hellevang has several suggestions for those finding themselves in need of temporary storage this fall for all or part of their sunflower production:
o If storing indoors, make sure the structure is sufficiently strong for the crop depth. This is of most concern with denser crops like wheat or corn. "Equivalent Fluid Density" (EFD) is the term engineers use to describe the force exerted by the crop, i.e., the load a structural wall must hold to safely store that crop. Wheat exerts a force on a wall of about 24 pounds per foot of grain depth; corn (shelled), 23 pounds; grain sorghum, 22 pounds.
Oil-type sunflower, however, exerts only 12 pounds per foot of depth, while for nonoils the figure is just nine pounds. So with oil sunflower, a 10-foot-high pile of seed would produce about 120 pounds of pressure per square foot at the bottom of the wall. "When we look at walls and the loads they'll have to bear, with sunflower we can go about 1.25 times as deep as with wheat," Hellevang notes, i.e., roughly the cube root of the EFD ratio.
The floor surface of an indoor facility also should be taken into account. "It's very important to keep ground moisture from coming into that grain, and it starts with selecting a site," Hellevang observes. "Is there good drainage around the building? Is there a good base to keep the moisture away from the grain?" If the structure has an earthen floor, plastic sheeting provides an effective barrier against moisture moving into the bottom layer of 'flowers.
Plastic may be appropriate even on concrete floors. "If we have wet conditions beneath [the concrete], the vapor goes through," Hellevang remarks, adding that cracks in the concrete also allow upward moisture migration. "It will 'wick up' into the grain, and you'll end up with quite a mound of grain near the floor that spoils and becomes worthless." That's naturally more of a concern if the sunflower remains in the storage for several weeks or longer.
o Consider covering outdoor piles. This obviously is not very feasible for a commercial elevator with a huge pile of sunflower that will be dried and is expected to be moved within a short period of time. For smaller on-farm piles, however, the investment could pay worthwhile dividends when the crop finally is marketed.
"We need to keep the moisture away," Hellevang stresses. "Once it's there, unless the pile is frozen, we're going to have problems."
Site selection is important. Piling the sunflower on ground that has good drainage - and perhaps even a crown to it - is a big plus. Again, a layer of plastic beneath the sunflower keeps soil moisture from moving into the pile; plus, it prevents dirt or gravel from becoming mixed in with the seeds and affecting quality.
Fall rains are a real threat to outdoor piles of sunflower seed. Hellevang says it takes about five pounds of water to raise the moisture content of 100 pounds of oil sunflower from 10 percent up to 15 percent. That's the equivalent of what's received in a one-inch rainfall. A slow, soaking two- to three-inch rainfall carries obvious implications for an uncovered pile.
"If we look at our precipitation patterns [in the Upper Midwest], we tend to get a fair amount of moisture during the fall period," Hellevang points out. "And it doesn't take a lot of rain to soak in and 'wet up' a lot of that product." Hauling wet seeds to market also means larger moisture discounts, he adds, noting that wetting the top several inches of a 10,000-bushel pile carries different economic implications (i.e., one's ability to sufficiently "blend off" with drier seeds below) than does wetting to a similar depth on a 100,000-bushel pile at a commercial elevator.
o Aerate piles expected to remain intact for an extended period. NDSU guidelines suggest a maximum moisture content of 10 percent for sunflower seeds in short-term (less than six months) storage under aeration. That recommendation was developed with standard steel-bin storage in mind, but it also would apply to temporary indoor or outdoor facilities.
"If it's going to be [in the pile] for just a week or two, we probably can get by without aeration," Hellevang advises. "Otherwise, I really encourage people to put a duct beneath the pile and hook on a fan. If we can move just a little air flow through to cool the pile, we can greatly enhance storability."
Quality deterioration is the result of moisture and temperature acting together. High moisture and cool temperatures will not cause storage problems, nor will low moisture and warm temperatures. The intent in aerating a temporary pile is to lower the temperature, not the moisture content, as one cannot realistically expect to dry the seeds.
"It doesn't take very much air flow to have a big impact," Hellevang advises. "We can use a 3/4-horsepower aeration fan and get some 12-inch duct relatively cheaply. If that duct is laid on the bottom of the pile and some air is moved to cool the sunflower, your chances of success are greatly increased. We don't need a drying fan of five to 10 horsepower. From an aeration standpoint, it takes very little air flow to change temperature."
o Monitor the pile closely. Piling 10-percent sunflower while ambient temperatures are 40-45 degrees or lower should provide for an extended safe storage period. But if the 'flowers are at 14- or 15-percent moisture and being piled when temperatures are 65-70 degrees, hot spots may develop within a day or two.
The frequency of monitoring thus depends on the conditions under which the sunflower is being piled. "If we get the crop inside a pole barn and we have an aeration system in there, we're probably looking at conditions not all that different from putting them in a bin," Hellevang exemplifies. "If we have a pile sitting outside, we need to be checking it more frequently - especially if it went in on the wet side."
Take time to probe piles that are rained upon, the NDSU drying/storage specialist adds. "The surface will tend to dry off; underneath is where the problems will develop," he points out. "We need to be probing below the surface.
"If you have damp sunflower and we're on the warm side, I'd be monitoring very closely," Hellevang concludes. -Don Lilleboe
Editor's Note: "Temporary Grain Storage," NDSU Extension Bulletin AE-84 (Revised), will be available in early September. Authored by Ken Hellevang, the publication includes a variety of helpful information pertaining to the temporary storage of various grains in both indoor and outdoor settings. Among its contents are instructions for the construction of structural walls of adequate strength to hold stored crops.
Bulletin AE-84 (Revised) can be obtained by North Dakota producers from their local NDSU Extension office. Interested persons from other states should contact the NDSU Ag Distribution Center at (701) 231-7882.