Getting grain in, getting moisture out

Harvest | Grain that comes off the field cool with high moisture content will require on-farm drying

Poor harvest conditions in many areas have increased the likelihood that a significant portion of this year’s crop will need to be conditioned before it is sold or stored.

The window for prairie farmers to harvest dry, high quality grain is closing, says Edgar Harder, a farmer from North Battleford, Sask.

“We’re going to get some warm weather yet. It’s going to happen,” said Harder last week.

“We can get good weather in October or at the end of September where the grain can become dry in the field. So the dry harvest is not finished yet.”

No one knows how much grain will come off dry.

Harder, a former Saskatchewan Agriculture employee, has been contracted by the province to answer questions about aeration, also known as natural air grain drying (NAGD).

He said aeration can be an effective, low-cost way to reduce the moisture content of binned grain, but it is only effective under certain conditions. And if harvest drags on, the chances of using natural air to dry down tough grain will diminish quickly.

“From now on you’re not going to get much drying from natural air any more unless we get a week or two weeks of warm weather,” he said.

There are limitations to how much drying can occur in NAGD systems. It depends on the temperature of the air that is being forced into the grain bin and its relative humidity, said Harder.

The temperature of the binned grain is another critical factor.

Tough grain that comes off the field warm can be dried by blowing cooler ambient air through the grain.

The relative humidity of the air drops as it is warmed by the heat in the grain, which allows it to pick up additional moisture.

The process works until the grain mass is cooled down to the ambient air temperature.

“The air being forced into the grain mass has to have the ability to pick up moisture,” said Harder.

“If your grain in the bin is still warm from harvest, then running cold air through it will warm up the air and allow it to pick up additional moisture.”

Conversely, if the grain mass is already cold, running cold air through it is not going to take out much moisture.

However, cooling grain will delay spoilage under the right conditions.

To achieve any appreciable degree of drying with aeration, producers should ensure that the relative humidity of the air going through the grain is below 60 percent, he said.

Some drying will occur if relative humidity is in the 60 to 70 percent range, but generally speaking, the lower the humidity, the better.

On its website, Saskatchewan Agriculture suggests that NAGD systems are most effective when the air entering the grain bin is 10 C or warmer and relative humidity is 70 percent or less.

Harder said he is often asked if running aeration fans at night will reduce the moisture content of stored grain.

The answer is maybe.

The ambient air temperature and relative humidity must be at proper levels. Otherwise, the air will not be able to pick up additional moisture as it passes through the pile.

Farmers hoping to reduce moisture content of binned grain using aeration should always ensure that the bin is adequately vented so moist, warm air can exit the structure after it has been forced through the grain.

If the bin roof panels are cold, moisture can condense on the under side from the warm humid air and drip back onto the top of the grain in the bin.

In crops that have yet to be harvested, the temperature of grain coming off the combine will be an important factor. In many cases, grain that comes off cool with excess moisture will require artificial drying that uses natural gas, propane or some other heat source.

Conditioning costs vary from elevator to elevator, but in most cases, grain terminals will dry grain at posted rates or they will blend tough grain with other grain that was dry at the time of delivery.

Most elevator locations give priority to producers who also agree to market their grain through that delivery point.

On-farm drying or custom drying may be the only other option for producers who are not in a position to deliver or sell their grain immediately.

According to Saskatchewan Agriculture, artificial heat sources can be added to aeration fans to achieve some level of drying.

In those cases, producers should follow basic rules:

  • Limit the increase in air temperature to 10 C.
  • Ensure that the minimum air temperature entering the grain is at least 5 C and preferably 10 C.
  • Ensure that the maximum air temperature entering the grain bin does not exceed 24 C.
  • Ensure that the air flow entering the grain is at least one cubic foot per minute per bushel. This may require partly filling bins rather than filling them to capacity.
  • Monitor grain once or twice a day to ensure it is drying and not spoiling because of the warmth generated in the grain mass.
  • Leave fans on for at least a few hours after the heat source has been removed to allow grain to cool adequately.

Hot air grain dryers are effective under almost any conditions, although the cost can be a tough pill to swallow.

Calculating the cost of on-farm drying can be difficult.

A few years ago, Alberta Agriculture posted a formula for estimating drying costs on its website.

It said producers must first determine moisture content of grain and then determine how many pounds of water per bushel must be removed. Once that has been determined, how much heat, in British thermal units (BTUs), required to dry a single bushel of grain can be calculated.

One gigajoule of natural gas or propane is the equivalent of roughly one million BTUs.

Farmers should also factor in additional costs such as labour and electricity required to run a dryer.

According to Saskatchewan Agriculture, grain dried in a hot air dryer regains moisture after it cools, which is known as moisture rebound.

Grain coming out of a dryer should always be cooled adequately before it is returned to storage.

Producers who have binned tough grain and those who are trying to use aeration to reduce moisture should always monitor grain closely and frequently to avoid spoilage.

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