Tuesday ranked as one of Chicago's Turnaround ones in the end, reversing a strong (upward) trend of the previous session.
But prices did not give up ground without a fight.
There was some good news for crop consumers in that weather models formed a consensus that this week's hot spell in the Midwest will end around Sunday-Monday as a cold front sweeps in from the north.
The midday run of the GFS weather model "was a little bearish in that it continues to confirm that the ridge will begin migrating south east this weekend", Darrell Holaday at Country Futures said.
"It will usher in cooler temperatures and will lead to increased rainfall opportunities."
Slim rain chances
But how much rain will actually fall?
"The data is also in strong agreement that the cold front itself will not have a lot of showers or thunderstorms with it, and any significant rains that do develop will probably be east the Mississippi River," David Tolleris at Country Futures said.
"There is simply not enough inflow from the Gulf of Mexico to feed moisture into the cold front and produce significant rains."
Mr Holaday added: "The market is not going to be comfortable until it sees rain fall."
And prospects for the European Union crop are deteriorating too.
But the improvement was enough to allow investors to remove a bit of the weather premium put in during the previous two sessions.
That was especially so for corn, for which hot weather is less of a risk, with the crop past its vulnerable pollination phase and, thanks to huge sowings, with some cushion for comfort even if yields do fall.
Furthermore, demand prospects have taken a knock with data on Friday showing the number of cattle on US feedlots significantly smaller than investors had expected.
Besides, the US harvest is ramping up, increasing supplies from that score, and investors have already covered some of their huge short positions in corn, a process which has been fuelling price rises.
"Open interest on corn was down 5,200 contracts on huge volume on Monday. This indicates mild short-covering," US Commodities said
Corn vs soybeans
December corn closed down 3.0% at $4.86 ¼ a bushel, surrendering its 50-day moving average after only one closing above it.
That also represented an underperformance with November soybeans, which shed 1.4% to $13.70 ½ a bushel, driving the soybean: corn ratio back up to 2.82.
But soybeans are more vulnerable at this time of year, during pod-setting and pod-filling, to heat.
And a US Department of Agriculture crop rating overnight showed the crop already deteriorating fast, with the "good" or "excellent" rating falling four points to 58% in the week to Sunday.
Indeed, US Commodities noted that "talk was aggressive yesterday that corn yields are now around 152 bushels per acre and soybeans are near 40 bushels per acre.
A crop at this level "would equate to a negative carryout on soybeans", in terms of stocks at the close of 2013-14, the broker said.
"This is impossible, but rationing would need to occur" to prevent it, implying elevated prices.
Furthermore, there looks to have been far less short covering in soybeans (albeit with less short to cover) than corn, with open interest was down 873 contracts on Monday.
Wheat, as has been its trend of late, lagged behind corn, meaning a drop of 0.5% to $6.63 ¾ a bushel in Chicago for December delivery.
There was some positive demand news in terms of Egypt's Gasc grain authority returning to tender, for the first time in three weeks, but this arrived after the market closed.
During trading hours, the highest profile tender was by Tunisia, for 84,000 tonne of wheat and 75,000 tonnes of barley.
Paris wheat for November closed unchanged at E191.75 a tonne, with French wheat already looking more competitive on the international stage.
London wheat for November soared 3.0% to £161.20 a tonne, catching up on moves elsewhere on Monday, when UK markets were closed for a national holiday.
Among soft commodities, raw sugar at least stabilised in negative territory after data from industry group Unica showed an acceleration in the Brazilian Centre South cane crush, and in sugar output - but with production of the sweetener not rising as much as it might have done.
Raw sugar for October ended down 0.9% in New York at 16.46 cents a pound.
And cotton for December fell 0.9% too, to 84.15 cents a pound, after the USDA crop condition data showed a further, small, improvement in the US crop.