Cropping

Strategies for managing high moisture grain in storage

Grain Central, November 3, 2020

STORM rain, hail damage and wet paddocks are adding to harvest stress across southern Queensland and northern New South Wales as growers work around the clock to get crops into storage.

But the challenge of harvesting doesn’t end at putting grain in the silo, with the Grains Research and Development Corporation’s (GRDC) Stored Grain Extension Team currently on call (1800 WEEVIL) to provide advice to growers storing grain at less than optimum moisture levels.

Queensland Department of Agriculture’s (DAF) senior development agronomist Philip Burrill, who is a member of the GRDC stored grain extension team, said there were several key points growers needed to keep front of mind when it came to storing grain with high moisture levels.

“The current unsettled weather conditions across much of southern Queensland and northern NSW has seen growers harvesting early with grain at moisture levels of 14 to 17 per cent,” Mr Burrill said.

“To avoid storage quality problems, growers need to act quickly once grain is in the silo. Grain respires like most living organisms, which means it takes in oxygen to use with carbohydrates, which in turn generates carbon dioxide, water and heat.

“When grain has a high moisture content and is warm, the rate of respiration increases significantly. This is what causes grain to self-heat, similarly to a wet bale of hay.

“Without aeration cooling of high moisture grain in storage, the temperature rapidly increases. For example, it can reach 40 degrees Celsius and more within a few hours of being in a silo.

“This can result in serious ‘bin burnt’ grain damage and creates ideal conditions for moulds and insect pests.”

Aeration, drying, blending

Mr Burrill said when growers were in a situation where they needed to harvest early and temporarily store grain, it was critical they had aeration cooling, as well as clear plans to dry grain or blend grain within three to five weeks.

“In most cases, grain can be safely held for a few weeks at 14 to 16 per cent moisture content with small aeration cooling fans running continuously, delivering airflows of at least two to four litres per second per tonne (2-4 L/s/t),” he said.

“Options for managing high moisture grain depends on the equipment available, but it is important to understand it is very difficult to reliably reduce moisture content using standard small aeration cooling fans (output 2-4 L/s/t) designed for cooling grain, not drying.”

In summary, Mr Burrill said small aeration fans were useful for temporarily holding wet grain, but growers needed a plan to dry grain that involved either a grain dryer (batch or continuous flow); aeration drying in silos with high output fans (15-25 L/s/t); or blending grain.

Silo set up

Tactics for silo set up for temporary storage of high moisture grain:

  • Run aeration fans continuously (24/7) after the first truck load goes into the silo. Ideally, use a silo with an aeration ducting design that ensures effective air distribution through wet grain. Silos with a wide base may require at least two fans opposite each other. Ensure silo roof vents or the top silo lid is open enough to ensure fan performance and that airflow is not restricted. Aeration fans need to be producing airflow rates of at least 2-4L/s/t.
  • Consider only filling two-thirds of the silo to reduce the grain depth and effectively increase air flow.
  • Do twice daily checks on grain temperature (use a grain probe – for example, Graintec Scientific – Toowoomba), silo fan operations and check grain smell at the top of the silo.
  • Run aeration fans day and night to keep wet grain cool. Ideally, use an automatic aeration controller set on ‘auto continuous’. This automatically turns fan off for a short time when air exceeds 85 per cent relative humidity.
  • If manually operating fans, growers should monitor the ambient temperature and relative humidity on-farm. If it the weather is wet and humidity is consistently above 85 per cent, they should turn off fans for short periods (two to four hours). Regularly check grain temperature with the aim of keeping it below 25 degrees Celsius. Remember, it is the average relative humidity of the air you are using while fans are running that is important. Short run periods for one to two hours of high humidity air during a rain storm should not cause problems as long as this is promptly followed by lower average relative humidity air (30 to 65 per cent relative humidity).
  • ‘Turning grain’ is an option to consider. After two to four days of having wet grain in the silo, auger the grain into a truck, then back into a silo. Moving grain around and turning it over helps to break up hot spots that can develop in a silo. This may be helpful if your aeration air distribution system/ducting is limited.

Equilibrium moisture content

Mr Burrill said it might also be helpful for growers to understand the equilibrium moisture content (EMC) for various grains and make use of the charts and graphs available.

“For example, the EMC figures for wheat when grain temperature is at 25˚C for three grain moisture content levels – of 12.5 per cent, 14 per cent and 16 per cent – results in the matching relative humidity that develops within the grain bulk of approximately 60 per cent, 70 per cent and 82 per cent,” he said.

“As a guide, during summer growers should aim for grain temperatures below 23˚C in storage and safe grain moisture contents that keep the grain bulk relative humidity below 60 per cent. This reduces the risk of damage caused by heat, grain moulds and storage pests.”

Source: GRDC

For advice from the GRDC Grain Storage Extension Team call 1800 WEEVIL.

For more detailed information about storing high moisture grain go to https://storedgrain.com.au/dealing-with-high-moisture-grain/.

Other useful resources:

How aeration works https://storedgrain.com.au/how-aeration-works-grdc-update/.

Aerating stored grain http://storedgrain.com.au/wp-content/uploads/2016/10/GRDC-Aeration-Book-2016_R2.pdf.

Water activity and equilibrium relative humidity – Len Caddick, CSIRO https://storedgrain.com.au/water-activity-and-equilibrium-relative-humidity-len-caddick-csiro/.

PAMI Equilibrium moisture content charts for grain management http://pami.ca/wp-content/uploads/2017/09/Equilibrium-Moisture-Content-Charts-for-Grain-Storage-Management_rev2.pdf.

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