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Workshop: Handling high moisture sorghum at harvest

GRDC grain storage specialist and DAF agronomist Philip Burrill is encouraging growers with high moisture sorghum to start harvest with a clear strategy in place to dry grain.
Photo: GRDC

Queensland and northern New South Wales sorghum growers are currently facing the common challenge of cooler weather slowing the dry-down of grain sorghum prior to harvest.

Department of Agriculture and Fisheries (DAF) senior development agronomist (Postharvest Grain Protection), Philip Burrill, says many growers were concerned about storage risks with the moisture content of some late sorghum crops well above the safe storage level of 13.5 per cent.

“There are growers who would like to harvest sorghum now, but it is sitting in the paddock with a 14-18 per cent moisture content,” he says.

“My advice is to harvest now if it looks like weather damage to grain or significant plant lodging is likely. However growers who harvest high moisture content sorghum need to have a clear strategy in place to avoid quality downgrades during storage.”

Mr Burrill, who works on GRDC's grain storage project, said the first steps for growers involved accurately checking the average moisture content in the paddock and organising on-farm equipment.

“The strategies that growers put in place depend on their equipment on-farm, but their options generally are to: dry grain immediately it is harvested, or temporarily hold sorghum using aeration cooling fans until grain drying can be organised, or to blend moisture grain with dry grain.”

But Mr Burrill warns growers that if they harvested sorghum with a grain temperature around 20-25˚C and moisture content above 16 per cent and put it in a silo without aeration cooling fans operating it will rapidly ‘self-heat’ and develop moulds.

“It is important growers understand the challenges of trying to reduce moisture content using standard small aeration cooling fans (output 2-4 L/s/t) designed for cooling grain, not drying,” he says.

“It is practically impossible to dry grain using a cooling fan. In explanation, if you have 100 tonnes of sorghum in a silo at 15.5 per cent moisture content and wish to remove two per cent moisture content to bring it down to 13.5 per cent, you actually need to remove two tonnes of water.

“That is 2000 litres of water and you can’t effectively remove that amount of moisture with standard low output aeration cooling fans.”

He also explains that using gas burners to add extra heat (4-6˚C) to the air in front of ‘low output’ aeration fans (2-4L/s/t) was not reliable or safe.

“This practice typically ends up over drying the grain in the bottom of the silo and actually causing grain damage with over wet grain problems developing at the top,” Mr Burrill says.

“But small aeration cooling fans are very useful when run continuously on silos to temporarily holding wet grain. The continuous low volume airflow will keep grain cool.”

In most circumstances, he says grain could be safely held for a few weeks at 14-16 per cent moisture content with small aeration cooling fans running continuously, delivering airflows of at least 2-4 litres per second per tonne.

“If growers decide to hold high moisture content sorghum in silos until they can put it through a grain dryer, then aeration fans need to be used to keep the grain from getting hot and prevent mould and bin-burnt grain damage,” Mr Burrill says.

“It is critical growers do daily checks on silo fan operations, grain temperature and smell.”

While it is possible to hold high moisture grain for short times with aeration fans, the ultimate aim is to reduce the moisture content of the grain with either a grain dryer or using aeration drying in silos.

“If choosing to use aeration drying in silos, growers will need large output fans, providing total air flows of 15-25 L/s/t. Remember, by only half or two thirds filling a silo it increases the airflow rates in terms of L/s/t,” Mr Burrill says.

“For drying, these large output fans are typically run for long run times of 18-22 hours per day for nine or more days, depending on ambient conditions.”

However, in some situations adding additional heat (4-6˚C) to this high airflow is worthwhile as it reduces ambient air humidity. For more information see GRDC’s reference note How aeration works.

In summary, the options for high moisture content sorghum are: grain dryer (batch or continuous flow); aeration drying in silos with high output fans (15-25 L/s/t); or for many growers, holding it in silos for a few weeks using the small aeration cooling fans (2-4L/s/t) prior to organising grain drying or blending.

Five tips for storing high moisture content sorghum:

  • Run aeration fans continuously (24/7) after the first truck load goes into the silo. If possible, use silos with at least two aeration fans to assist with good air distribution through wet grain and trash. Clean the impeller on older aeration fans, as accumulated dust will reduce airflow outputs. Ensure silo roof vents/top silo lid is open for good ventilation.
  • High moisture sorghum (14-16 per cent) can be held safely for a few weeks with small aerators, provided fans are left running so grain does not get hot. Only turn small fans off briefly when outside air relative humidity remains above 85 per cent for more than 3-4 hours. With fog or mist, fans should be off.
  • A good quality ‘automatic aeration fan controller’ significantly improves reliability, safety and the final results when managing high moisture grain.
  • Have a grain temperature probe (Graintec Scientific - Toowoomba) to check the temperature of high moisture content sorghum in storage at least twice a day. Keep grain well below 35˚C. Augering the grain out of a silo into a truck – ‘turning the grain’ – will help manage wet/warm grain in storage.
  • Use a good quality grain moisture meter that has been serviced and checked regularly.
  • Aim to dry or blend sorghum down to less than 13.5 per cent moisture content within 3-5 weeks after harvest.

More information: Dealing with high moisture grain or GRDC Update - How aeration works.

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