Huge numbers of spontaneous combustions of hay seem to be most common in stacks of large square bales made from drought-stressed cereal crops.

This is according to Australian Fodder Industry Association chair, Lyall Schulz, whose organisation is one of several now keen to look harder at the causes.

Mr Schulz says one hay fire a year is too many.

The association’s sources tally total hayshed fires in NSW, South Australia, Victoria and Queensland above 400 so far this season, devastation costing millions of dollars.

In some cases, individual round bales have ignited in the paddock.

Mr Schulz says one possible cause of the fires is that the "sappy heads in these crops had not fully emerged from the boot, leaving the hay difficult to cure and making it difficult to accurately measure its moisture".

Lyall Schulz (centre), farms on Yorke Peninsula in South Australia with sons, Brett (left) and Scott. He is encouraging colleagues to help research the causes, particularly if they have experienced hay fires.

Other theories include high levels of sugar in drought-stressed crops leading to increased microbial activity and heating, rushed baling of high moisture hay, poor calibration of moisture meters leading to inaccurate readings of moisture in hay, and a lack of effective hay conditioning.

With the peak danger period for spontaneous combustions now past, the association is asking members of the fodder industry and other stakeholders to help test the theories.

A confidential survey invites hay owners to say why they think so much has gone up in smoke.

The association is encouraging members who have either baled or stacked hay, or who own hay in stacks to complete the survey, particularly if they have experienced fires.

The association is working with the NSW and Victorian Departments of Primary Industries (DPI), the EH Graham Centre at Wagga Wagga, and representatives from the fires services to undertake research into hay fires.

The survey will be available over the coming months.

Individual information will be kept confidential and will only be displayed in an aggregated format.

Shed fires are not the only cause of economic losses.

"Hay that has not been properly cured can become mouldy and unpalatable, and even dangerous to stock, making mouldy hay worthless," livestock research officer with NSW DPI at Wagga Wagga, John Piltz, said.

A hay fire fact sheet is available from the Australian Fodder Industry Association website.

Contact John Piltz, Wagga Wagga, (02) 6938 1839 or Colin Peace, Victoria, (03) 9890 6855