Is natural air drying right for your bins?

Using forced natural air to dry tough grain is a bit like farming.

There’s never a guarantee of success but a little bit of know-how can go a long way.

John Ippolito, a regional crop specialist with Saskatchewan Agriculture, says there are several factors that determine whether forced natural air has the ability to remove moisture from stored grain.

One of the most important is air flow.

“Probably the biggest issue that we try to sort out right away is the difference between what we call aeration and what we call natural air grain drying,” said Ippolito.

“For aeration, in the true sense of the word, all we’re trying to accomplish is to cool the grain mass down or to make the temperature of that grain uniform, so we’re using relatively low air flow rates. The common recommendation is somewhere between one-tenth and two-tenths of a cubic foot per minute per bushel.

“For natural air grain drying to be effective, we’re looking for air flow rates in the range of one to two cubic feet per bushel per minute, so nearly 10 times the air flow that we would expect in aeration.”

The basic principle behind natural air grain drying is that warm ambient air, when forced through stored grain, will absorb moisture as it moves though the grain mass.

Air flow is one factor that determines drying capacity.

But there are other factors as well, said Joy Agnew of PAMI, an agency that carries out agricultural equipment testing.

Ambient air temperature and relative humidity also affect the rate of moisture removal.

On its website, PAMI uses an Equilibrium Moisture Content (EMC) chart to illustrate the air’s capacity to dry stored grain under a variety of temperature and relative humidity scenarios.

In a nutshell, warm air with low relative humidity should result in good drying conditions, provided that air flow rates are adequate.

Conversely, as outside air temperatures decline and relative humidity levels rise, the drying capacity of ambient air is diminished.

PAMI’s EMC chart can be viewed on-line at

But the story doesn’t end there, Agnew added.

Still other factors, including the type of grain being stored and the temperature of the stored grain itself, can also affect dry-down rates under natural air grain drying systems.

Saving stored grain

  • Temperature differences between the outside air and inside stored grain can cause air circulation that traps moisture and damages grain.
  • Hot grain is especially prone to condensation. In fall and winter, this condensation occurs near the roof in the centre of the bin. In spring and summer, it happens at the bin’s bottom. Grain should be turned or aerated to prevent damage.
  • Any crusting on the surface of pulse crops must be removed shortly after it develops or the crop risks downgrading. Avoid surface piles where possible because this promotes uneven drying. Fans can help cool grain and dry crops.
  • Use bin monitoring cables to measure temperature gradients from the top to the bottom through the core.
  • Inspect bins monthly once they are stabilized.

For example, grain that goes into the bin warm and tough is generally easier to dry using forced air than grain that goes into the bin cool and tough.

In addition, growers who are hoping to achieve some degree of drying using forced natural air should ensure their bins have proper ventilation so moist air has an opportunity to escape and condensation inside the bin is minimized.

Potential benefits of a natural air grain drying system can be quickly negated if the bin has inadequate venting, Ippolito said.

Ventilation requirements at the top of the bin are greater in systems that use high volume fans.

In the fall of 2016, many prairie growers added supplemental heat to aeration systems to dry down grain that came off the fields late and tough.

Supplemental heat provides greater flexibility for growers who are managing tough grain in storage.

Agnew is in the process of crunching numbers to determine if there s an economic case for using aeration fans and supplemental heat more routinely during the early harvest period.

If tough grain can be taken off early during the warmer part of the harvest season, drying is more likely to be achieved in the bin given that ambient daytime air temperatures and grain temperatures are relatively high.

With the right systems, growers could get an early jump on harvest and dry down stored grain at a relatively low cost rather than waiting for crops to dry naturally in the field and losing valuable time that could otherwise be spent in the combine.

Stay safe while checking bins

It’s like drowning and it happens just as fast. You get sucked down into a pile of moving grain and the more you struggle, the faster you sink. After just five to six minutes, you can die of suffocation. How do you prevent it?

  • Before entering the bin, stop the flow of grain, shut off any mechanical equipment and allow for bin ventilation.
  • Break up surface crusts from outside the bin through a roof door using a wooden or plastic pole or a weighted line.
  • If you must enter a bin, stay above the material and never stand on it.
  • Wear a proper safety belt with securely fastened “life lines” when working above the material.
  • Always have a standby around.

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