It wasn't just agricultural commodities which suffered a sell-off.

But they certainly took very seriously their contribution to the retreat in financial markets as the optimism injected last week by the US commitment to a potentially unlimited bond-buying programme turned to sand.

New York Federal Reserve bank issued a reminder of the task facing US authorities in propping up the world's biggest economy when its Empire State manufacturing survey came in with its lowest reading since April 2009.

US-China spat

Meanwhile, commodity markets struggled against a mildly reviving dollar, whose strength makes dollar-denominated assets less appealing as exports, and concerns for consumption fostered by continued concerns over Chinese demand – which were not done any favours by a US-Sino trade dispute.

China on Monday filed a complaint with the World Trade Organization over a US law on tariffs aimed at penalising subsidised exports from other countries, hours after Washington announced a wide-ranging complaint against Beijing support for car exports.

China is a large importer of a range of US goods, including agricultural commodities such as cotton, corn and soybeans, besides the likes of oil which, for Brent crude, dropped more than 4% to $111.50 a barrel at one point.

The average commodity, as measured by the CRB index, fell 2.0%.

Winners turn losers

Even so, there were plenty of agricultural commodities which fell far further than that – and not all in Chicago – as investors who had been stocking up in crops extended a cut in long positions evident in regulatory data.

"Funds have been taking profit and like a flock of sheep when one runs for the exit they all tend to follow triggering stop losses," grain traders at a major European commodities house said.

The latest data from the US regulator, the CFTC, showed only cocoa and coffee among major crops traded on US exchanges enjoying an increase in speculators' net long positions in the latest week.

On Monday, they were amongst the worst hit as speculators, and others, turned tail.

New York cocoa for December dropped 2.2% to $2,584 per tonne, despite repeated concerns, voiced by Commerzbank, over "unusually dry conditions" in West Africa, the main producing region.

'Traders liquidated'

New York arabica coffee for December tumbled 3.0% to 175.65 cents a pound, as producer selling added to pressure from fund liquidation.

"Throughout the morning session we continued to see speculative support. But each attempt higher stalled as origin, light trade and even arbitrage sellers where ever present," Sucden Financial said.

"We did see one last attempt to break higher, but as this failed day traders liquidated and gains where slowly eradicated.

"As we have come to expect of coffee in the recent weeks the downwards momentum picked up, triggering stops through the 180-cents-a-pound area," meaning selling pressure begot more selling pressure.

Worst performance in 10 months

But the most dramatic losses were seen in Chicago, where wheat - in which speculators have built an unusually large long position, yet in which they have rarely been shy in selling down – turned tail.

The December contract closed down 5.2% at $8.76 as bushel, the worst performance for a front contract since January.

Adding to the broader negative sentiment was a forecast for rain for Western Australia, where dryness has sparked concerns of a halving in the harvest.

Syria, which earlier issued a tender for 100,000 tonnes of the grain, looks like it may get its order for less than it had thought.

'Not your dad's markets'

In the end, that outdid soybeans, even though the oilseed had a stack of negative factors ranged against it – although its progress south was curtailed by hitting the maximum loss of $0.70 a bushel allowed by Chicago.

"The steepness of the sell-off should not surprise us anymore," Darrell Holaday at Country Futures said.

"Remember, these are not your dad's markets. They move when they need to move."

One big negative was from the harvest – both from pace, giving a temporary boost to supply hopes, and better-than-forecast yields, suggesting a more permanent one.

"Yields are better than expected as the harvest gains momentum. This is especially true in the western Corn Belt on soybeans," broker US Commodities said.

Seedings unaccounted for?

Furthermore, there were improved rain hopes rose for central Brazil, where dry weather had promised a slow start to plantings, for which the state-imposed sowing window opened on Saturday.

Then there was talk of China's Sinograin releasing a further 3m-4m tonnes of soybeans from state inventories in the top importing country.

"It would be interesting to know if they had that much at easy disposal. But if so, that would be a step up from the 400,000 tones they have been selling at auctions of late," Jerry Gidel, chief feed grains analyst at Rice Dairy, said.

And to top it all, monthly data from the Farm Service Agency, part of the US Department of Agriculture, showed US soybean plantings submitted to the organisation's support programmes at 75.7m acres.

That is 800,000 acres bigger than last month's estimate and, in not accounting for all plantings, suggested to some analysts a bigger total figure than the 74.6m acres that the USDA has counted in.

Chicago soybeans for November closed limit down, 4.0% at $16.69 a bushel, the lot's lowest finish for nearly four weeks.

'Aflatoxin fear…'

Corn faced many of the same pressures as soybeans, in terms of harvest pressure, and some extra acres.

The FSA also raised its idea of corn sowings, as indicated by farmers' returns, by 800,000 acres to 93.8m acres, if still below an official USDA figure of 96.4m acres.

Besides, the market was giving farmers little reason to hold on for high prices, with the front four contracts, out to July 2013, trading pretty much in line.

"The carry in corn is not sufficient to hold on for opportunities," US Commodities said.

"The aflatoxin fear, the poor quality of corn and the insurance being set in October are all adding up to selling off the combine in corn".

Corn for December dropped 4.9% to $7.48 a bushel.