It was actually tricky for commodities in general to rise on Wednesday, amid worries over the potential for a US strike on Syria.
Something of a "risk off" feeling helped the dollar add 0.7% against a basket of currencies, adding to pressure on raw material prices.
A stronger dollar undermines prices of dollar-denominated commodities by making them less affordable to buyers in other currencies.
Even Brent crude fell, down 0.7% back below $115 a barrel, despite being something of a potential winner in price terms from Syrian disruption, if unrest prove contagious.
As Nomura said, it is the threat "that Syria becomes a flashpoint for more disruptive developments elsewhere, for example, Iraq, Iran, that poses the deeper risk for markets".
The broad CRB commodities index fell 0.8%.
And soybeans did their bit, and more, to bring the index down, depressed by a cocktail of factors.
The main one was the turn slightly wetter in the US weather outlook, for next week at least.
"The forecast has trended wetter in the eastern Midwest and north eastern Plains," weather service MDA said.
"The continued dry pattern across the west central Midwest will maintain moisture shortages, but rains in north western and eastern areas will favour late soybean growth."
And while temperatures are looking a little higher – Commodity Weather Group says this month could be one of the warmest so far this century – that has an advantage.
It is a "definite plus for delayed row crop development", said Richard Feltes at broker RJ O'Brien.
And it offset some of the yield worries provoked by estimates from Allendale and Lanworth, well below the figure the USDA is factoring in.
'Made the market nervous'
As an extra setback for soybeans, there was talk that China will extend auctions of the oilseed from state inventories.
"China announced they were auctioning off additional soybeans out of reserves, of at least 2m tonnes," Darrell Holaday at broker Country Futures said.
"That has made the soybean market nervous."
Mr Feltes reported the rumours as being that "China will offer another 2m-3m tonnes of soybean reserves to the domestic market in December".
Whatever, it means a potential curb on private purchases of the oilseed from the top soybean-importing country.
And that on top of the technical factors reported earlier, one being from the failure of Chicago's November contract to break much above $14.09 a bushel in the last session for a third successive time.
"Failure to trade through the previous high of $14.09 ¾ a bushel on the November contract in yesterday's session is offering technical weakness," Benson Quinn Commodities said.
And then there was the pull from December corn futures, with the new crop soybean: corn ratio ending the last session at an elevated 2.91: 1, having been below 2.20:1 early in the year.
With corn falling too, albeit not as fast, soybeans for November closed down 2.5% at $13.52 ½ a bushel.
Corn for December fell, by 1.3% to $4.69 ½ a bushel, albeit pulling the soybean: corn ratio back to 2.88: 1 as it did so.
The grain was not so affected by the weather outlook, with the crop less affected at this time of year by heat and dryness than soybeans – meaning less weather premium to build back in from latest outlooks.
Indeed, Allendale proved relatively upbeat on corn yield prospects, pegging the figure at 153.4 bushels per acre, only 1.0 bushel per acre short of the current US Department of Agriculture estimate, and in line with what investors have been thinking anyway.
"Overall corn US corn yields have moved to an industry consensus of 154 and 41.1 for soybeans," Country Futures's Darrell Holaday said.
'Very difficult to scare up buying'
However, corn is feeling pressure from the spreading US harvest, which in ramping up supplies gives buyers some market power.
"It is very difficult to scare up buying this time of year," Mr Hoalday said.
"There is uncertainty about crop size, but we are also on the verge of fully-fledged harvest.
"It is worth noting is that December corn dropped $1.30 per bushel in the month of September last year despite a disastrous corn yield."
Benson Quinn Commodities said that corn harvest in the South was "steadily advancing and so far yield reports have been impressive".
At Allendale, company president Paul Georgy said: "There have been more corn yield reports out of the mid-south at 230-260 bushel per acre."
And this when competition on export markets appears pretty fierce, with lots of talk of cheap Brazilian and Ukrainian corn offers.
Mr Holaday said: "The export pace of corn and soybeans out Brazil is moving at a record pace and is eating into US export potential.
"The market has been focused on supply issues, but it is not turning to the demand side."
Wheat, against that background, did pretty well in Chicago, despite another Egyptian tender going by without a purchase of US supplies.
But that had been expected, given the competitiveness of Black Sea supplies (which indeed swept the board again).
What did help was concerns over dryness in Argentina and Australia, the top southern hemisphere growers, with frost damage an issue in the latter too after temperatures fell to -4 degrees Celsius (25 degrees Fahrenheit) last week.
Lanworth trimmed its forecast for the Australian crop to 24.9m tonnes, "on the basis of frost/freeze damage and historically low August precipitation in Queensland and northern New South Wales".
'Dryness will stress wheat'
As for Argentina, MDA said while rain has improved moisture "a bit" for southern Buenos Aires province, "dryness continues to stress wheat elsewhere across the region.
And although some parts of Buenos Aires should receive rains next week, "dryness will continue to stress wheat in La Pampa, western Buenos Aires, and Cordoba".
Wheat edged 0.2% lower to $6.46 ¼ a bushel in Chicago, for December delivery, and by 0.1% to $6.98 a bushel in Kansas, for the same month.
In Paris, November wheat dropped 0.5% to E188.75 a tonne, after the Egyptian tender results showed French wheat still not competitive with Black Sea supplies.
Among soft commodities, the retreat of Brazil's real, after earlier gains, washed out resilience in arabica coffee and raw sugar futures.
Arabica beans for December closed down 0.3% at 116.85 cents a pound, just above a fresh four-year low for a nearest-but-one contract.
Raw sugar for October eased 0.5% to 16.38 cents a pound, amid some idea of minimal volatility to come for now.
"Next week sees both London October white sugar futures expiry and October New York options expiry," Nick Penney, senior trader at Sucden Financial, said.
"The market in New York is stuck between 16 and 17 cents a pound and we are heading for the usual options lock.
"We will be looking at open interest on the more relevant strikes closer to expiry, but in the absence of any meaningful fresh fundamental news, we don't anticipate much movement in the meantime."
New York cotton for December edged 0.04 cents higher to 82.75 cents a pound, as support from a deterioration in US crop conditions met cautions over prospects for a sharp deterioration in Chinese imports.