Test: Recent rainfall may have put your hay at risk

22 January 2024

Farmers need to be mindful that even well-made hay can still be prone to spontaneous combustion.

Agriculture Victoria Program Manager for Dairy – North, Brett Davidson said spontaneous combustion is usually caused by excess moisture at baling.

‘Fires can also start due to heavy rainfall events which has soaked into stacks.

‘Intense rainfall could compromise even well covered stacks, as water can pool at the base of a stack, seep into gaps or could be blown under covers.’

For those with moisture meters, ideally hay moisture levels should be in the ranges below.

Recommended moisture contents (%) for safe storage of hay

Type of bale

Recommended moisture content ranges for baling hay (%)

Small square bales

16 – 18

Large round bales

14 - 16

Large square bales

12 - 14

Export hay

< 12

Even at 2 – 3% above the maximum moisture contents recommended in the table, hay will start to lose dry matter (DM) and nutritive value due to plant respiration or mould growth, resulting in heating of the bale/stack.

Higher moisture contents, well above the maximum (greater than 4%), could lead to more mould and heating, possibly resulting in spontaneous combustion.

Mr Davidson said it will be vitally important to regularly monitor the stack from one week after rainfall for signs of heating.

These are:

Mr Davidson said unfortunately, much of the heating will occur in the stack centre which is difficult to pick up.  To try and get an idea on how hot a stack has become, using a crowbar pushed into the stack as far as possible is one strategy that can be used.

‘After a couple of hours, remove the crowbar and feel how hot it is.’

A rough guideline to check a haystacks temperature using a crowbar, is as follows:

Mr Davidson said an alternative monitoring method can be achieved by using thermal couplings, which can be placed into various areas of the stack at stacking and monitored simply and regularly.

Media contact: Sarah Hetherington

Phone: 0409 405 639