Busting storage myths: Is air drier at night?


There are a lot of competing narratives around grain storage; some may even call them myths.

For people who wanted to clear away some of the smoke and mirrors around grain storage, there was a special presentation of “Myth Busters” at the Ag in Motion event this year. It was hosted by Joy Agnew, project manager with the Prairie Agricultural Machinery Institute (PAMI.)

We caught up with Agnew so she could let us, and you, in on some secrets. “My goal is just to give producers as much information as I can so they can make their own management decisions.”

There were five storage myths that Joy discussed in her presentation, and we discussed one that seems to be particularly contentious — if, in fact, air is drier at night. That immediately led to that famous phrase, “Well, technically speaking…” and, yes, technically night air can be drier (as in, holding less water), however it also simply can’t hold as much water, because it’s cooler.  (Story continues below…)

Agnew gets down to brass tacks about what’s actually happening in the interview above: Cool air can’t hold as much moisture as warm air, so air at night is more likely to have as much water as it can hold, even if it has less water, in total.

“But when it comes to drying grain you are more concerned or interested in how much more water the air can hold before it becomes saturated,” she notes.

She uses the capacity of a water glass as a proxy for the water-holding capacity of air. “My water glass analogy is basically showing that air during the day can hold more water, so it’s a big glass, air at night is a smaller glass. And relative humidity is essentially, percentage of full, so air during the day is a big glass. If it’s 50% (relative) humidity day, it is half-full. So that means there’s still that much more space to take up moisture.”

Like almost everything in farming, though, there are other things to take into consideration, such as the temperature of the grain.

The water glass analogy also works well in describing what happens if the grain is cooler than the air. Agnew says, “Warm air, let’s say a big glass that’s half full, if you pass that through cool grain, that air is going to cool off, and so the glass is going to shrink, but the water that was already in the glass has to go somewhere.” In this context, “somewhere” is into the grain.

The biggest problem with water going into the grain is that it will be mostly concentrated at the point of contact, creating a high moisture spot. Luckily the cause of the problem is also the solution — just continue to run the fans, she says.

PAMI posts its research on the PAMI website. For more information on storage, click here. For other topics, click here.

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