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For over 20 years, Advantage Plastics has been manufacturing and supplying New Zealand-wide a large range of on-farm storage & handling equipment.
While the target for long-term storage should be to get heap or silo temps down to single figures, fans should be on as soon as ambient air is 3-4 deg C below the grain temperature, says storage specialist Richard Flach, of equipment supplier Flach & Leroy.
“Aim to have grain below 15 deg C within two weeks of harvest, and below 12 deg C within 3 months.
“For example, if the grain is coming in at 20 deg C, you can use air at 15 deg C to cool it, so do it in steps making the most of cool ambient conditions rather than waiting for a frosty night.”
Flach points out it requires much less energy to cool grain than to dry it.
“A useful analogy is a mug of tea - it cools down far quicker than it evaporates!”
It’s important to cool grain as it comes in off the field because the main insect pests of stored grain, particularly grain weevil, can multiply rapidly above 10 deg C, irrespective of the moisture content, he points out.
Preventative treatment with organophosphate (OP) insecticide such as Actellic (pirimiphos-methyl) at intake is an expensive option compared to cooling and, while still permitted in New Zealand, there are concerns with residues entering food chain.
“OP’s aren’t allowed in the UK anymore,” he notes.
That said, there may be some merit in treating the top layer of grain due to localised increases in moisture content because of condensation come winter, he adds.
Relatively low air volume is required to achieve effective cooling, as little as 0.15 cubic metres/minute/t.
Typically, a small centrifugal fan can provide this, but the air distribution system must be appropriate to the store type.
Manual management of fans can work, but it is easy to forget to turn a fan off in the morning, or fail to notice if temperatures rise unexpectedly,
warns Flach.
“If that happens, at best you’ll be doing no good at all, and at worst, warming the grain back up.
“Better to have a simple differential thermostat which measures the grain temperature and the ambient temperature, and only runs the fan if the ambient temperature is 3 or 4 deg C lower than the grain temperature.”
Accurate and regular sampling and monitoring of stored crop will help detect potential problems early, minimising losses and or the cost of corrective action.
“Any localised increase in temperature could indicate fungi, sprouting or insects. Any increase in moisture content could indicate condensation, leaks, or insects.”
No storage fungi grow if grain is stored below 14.5% moisture content and mites are unable to breed if the moisture is below 14.5%, he adds.
