It All Comes Back to Basics
Sunday, August 1, 1999
filed under: Harvest/Storage
'Proper Management Should Ensure Retention of Stored Sunflower Seed Quality'
Out of Sight, Out of Mind
This familiar adage sounds benign, but it can produce some nasty
consequences for sunflower in storage. Like other grains, stored
sunflower seed literally passes "out of sight" the moment it is augered
or moved pneumatically into the bin. Hopefully, however, it is never
remains "out of mind" for too long. Should that occur, the eventual
result may be much more ominous: "out of quality" seeds and a producer
who ends up "out of income."
In light of the technology and information available today, Ken
Hellevang contends there is no legitimate reason for the quality of
sunflower seed - or any other grain - to deteriorate significantly while
in storage. Nonetheless, the North Dakota State University extension ag
engineer fielded numerous calls this past winter and spring regarding
stored sunflower seed that had incurred serious mold and/or insect
Insects were making their presence known by Thanksgiving in crops
which had not been adequately cooled after being binned. "Then, in
March, as people were hauling in sunflower and much of it was being
tested by the grain labs, there were reports of a lot of heat-damaged
sunflower," Hellevang relates. Heat damage would indicate
higher-than-desired moisture contents; but also that the grain had not
been adequately cooled, he says.
Why hadn't the problems been detected earlier? Either they weren't sufficiently severe to be noticed, or
monitoring of the seeds wasn't sufficiently thorough.
The extent of the past year's storage problems was likely
exasperated by the size of the 1998 crop, the relatively mild Upper
Midwest winter - and by the fact that some seeds were stored in
temporary facilities where an adequate aeration system may not have
For a number of years, North Dakota State University ag engineers
have listed 10 percent as the maximum recommended moisture content for
oil-type sunflower seeds going into short-term storage (less than six
months), and eight percent as the maximum for oils in long-term
storage. For nonoils, the numbers are 11 and 10 percent,
There are four ways in which these goals can be met:
1. Via Mother Nature, i.e., harvesting when seeds are already at
or below these moisture levels. That's not hard to achieve in the High
Plains, where hot, dry autumn days commonly result in seeds harvested at
well below 10-percent moisture.
2. With a high-temperature dryer. There, as veteran producers
know, one has to remain cognizant of the 'moisture rebound' phenomenon.
The moisture content being read by a moisture meter is more influenced
by the outside of the seed. But since the interior nutmeat is of a
different material and moisture than the seed hull, such a reading may
be too low by one, two or even more percentage points, depending upon
how wet the seeds were and how quickly they were dried. So a sealed
sample must be allowed to equilibrilize (usually taking between 12 to 24
hours) before a true reading of the entire seed's moisture content can
3. Inside the bin via a natural-air/low-temperature drying
system. Efficient natural-air/low-temp systems utilize a fully
perforated floor for uniformity and thoroughness of drying. The drying
process can take up to several weeks, depending upon airflow rate,
climatic conditions and the initial moisture content of the binned
seeds. Sunflower seeds going into storage at 15-percent moisture, for
example, require a minimum airflow rate of 0.5 cfm per bushel; at
17-percent moisture, the minimum would be 1.0 cfm.
4. Aeration. Moving sufficient ambient air through a bin can
remove some moisture over time - but it's not the answer if one needs to
dry down the sunflower by more than one or two points. That's
particularly true if the producer is aerating in late fall and/or uses a
"Y" duct system versus a fully perforated bin floor.
The good news, says Ken Hellevang, is that sunflower - particularly
in the Upper Midwest - does not have to be dried down to those
recommended storage moisture levels if - and this is a very large if - the seeds are kept sufficiently cool while in storage.
What's meant by "sufficiently cool?"
The table on page 8 lists the approximate allowable storage time
for cereal grains and sunflower. (Please call the NSA for a reprint of the table.) Wheat at 17 percent moisture, for
example, can be stored for up to 130 days if kept at 50 degrees F. For
17-percent sunflower, however, the upper limit at 50 degrees is only
about 30 days. Hellevang's rule of thumb is that dropping the
temperature by 10 degrees roughly doubles the allowable storage time.
"That's why it's so important we make use of aeration to control
the temperature," he states. "If you cannot control the temperature,
you must drop the moisture.
"Grain can be stored at higher moisture contents as long as we keep
the grain cold," the NDSU ag engineer continues. "If we pull down the
temperature and keep it at freezing, we can hold seeds over winter with
no storage problems. So when samples come in with heat damage, that
tells me they're not operating the aeration system to keep the storage
cool - because even if the seeds were put in wet, if the air was on and
kept things cool, they shouldn't have had problems."
With wet seeds, Hellevang emphasizes the need to turn on the
aeration fans in a timely fashion, not waiting until November out of a
desire to be moving colder air through the bin. He encourages producers
to begin cooling as soon as the outside air temperature is 10 to 15
degrees below the interior bin temperature. Doing so has a couple key
* It will limit insect reproduction. Grain temperatures of 70 to
80 degrees are not only optimum for molds; they're also ideal for
insects. "When we get the temperature down in the 50- to 60-degree
range, insect reproduction is reduced; in the 30- to 50-degree bracket,
insects are dormant; and if we bring our temp below 30 and hold it there
for an extended period, we can actually kill insects," Hellevang
* "With our larger bins, we get moisture migration, where - because
of temperature differences - the moisture accumulates in the top center
of the bin. That appears to be driven whenever we have about a
20-degree differential within the bin. By keeping the temperature
approximately approaching outdoor temperatures as they drop, we prevent
the crusting problem that occurs with moisture migration."
Hellevang adds that controlling binned grain temperatures does not
require a large fan - particularly with a lower-density crop like
sunflower. "Just a small fan, and perhaps a duct distribution system,
is all that's required to cool that grain. We can control a
10,000-bushel bin with a 1.5-horsepower fan."
The bottom line when it comes to protecting stored sunflower seed
quality is one of 'reventive medicine,'Hellevang emphasizes. "It all
comes back to basics," he says. "The first thing we need to know is
moisture content. As the grain is going into storage - and then after
it's in storage - we need to be taking samples and checking the moisture
content. We also need to do temperature sampling within the storage,
because that's really what will determine the storability of that crop."
Once the crop is in the bin and has been thoroughly checked, "I
recommend producers be out there every couple weeks so they know what
the moisture contents are and what the temperatures are," Hellevang
advises. "Then, after the grain has cooled down to near freezing,
checking the grain probably once a month during the middle of winter is
fine. But they still need to be out there doing some probing -
particularly as temperatures begin to warm up in the spring." - Don