Australia's most lucrative export dived 1.2 per cent to $US77.70 a tonne, taking the month's losses to 8 per cent.

But it's not just the Pilbara feeling the pinch. Wheat crops from Dimboola to Dubbo are also feeling the pinch of lower prices.

Booming wheat production across the globe has hammered the price of the grain – Australia's sixth biggest export, which was worth about $6 billion in 2013 – to a four-year low.

The global price for wheat slid 12.5 per cent to $US481.25 in the past month, extending the losses from its year peak in May to 36.8 per cent.

Analysts say rising supply from Europe and the Black Sea region has outstripped demand, and prices are expected to remain soft until early next year.

It's not the only crop notching up losses. Corn, a key industrial food and drink-making material, has sunk 9.3 per cent for the month, while soybeans have plummeted 15.24 per cent.

Again, the falls have been attributed to oversupply. The US Department of Agriculture has forecast global oilseed supply to hit a record 528 million tonnes in 2014-15.

Waning demand, particularly from Asia, has also hit the gold price, which has continued its slump, falling 5.6 per cent in September to $US1215.36 an ounce.

ANZ gold analyst Victor Thianpiriya said it was a case of Chinese buyers snapping up too much of the metal last year.

"Maybe eyes-too-big-for-the-stomach sort of syndrome where they bought too much and now they are suffering from a case of a little bit of indigestion," he said.

"That's going to take a few quarters to work through and is going to keep the gold price depressed and physical demand on the sidelines."

But Edmund C. Moy, former director of the US Mint under two presidents and now chief strategist for Fortress Gold Group, said Asian buyers were starting to regain their appetite for gold.

"India's demand jumped last month in spite of continued import restrictions and demand is likely to increase ahead of Dhanteras and Diwali festivals, and the upcoming wedding season," Mr Moy said.

"Expect demand to increase when typically price-sensitive Asian buyers sense the market is hitting bottom."

Losses have spilled into other metals. Aluminium, which generated $3.3 billion in Australian exports in 2013-14, slumped 6.5 per cent in the past month. Three-month futures were trading at $US1950.50 per tonne on Monday.

ANZ commodity strategist Daniel Hynes said there were signs that demand for lightweight metal was improving after several years where numerous smelters were shutdown, putting a cap on aluminium supply.

Nickel prices have also lost momentum, falling 8 per cent in the past month to its lowest level since March last year.

"A factor in recent falls has been a build up of LME nickel stocks. Inventories have risen almost 16 per cent since the start of July," ANZ analysts said.

Thermal coal has continued to be extremely weak. Contract prices recently set for delivery from October 1 to September 30, 2015 were set at $US73.85 per tonne. Last year's October price was $US85.80 and the April price was $US81.80.

Beef, Australia's 10th biggest export earner, worth about $4.6 billion last year, was the bright spark among the country's key commodities.

The Australian benchmark price, the Eastern Young Cattle Indicator, rose 6.9 per cent in September to $3.57 a kilogram.

NAB agribusiness analysts expect prices to remain on the upside over the coming year as producers look to rebuild herds, especially in the event of a decent northern wet season.