Could it keep the key support level of its 100-day moving average, at $6.85 a bushel, at its back? The average is a key level for chart-watchers, and has provided resistance to selling, as in the last session.
In fact, "December corn has not closed below the 100-day since mid-July", Mike Mawdsley at Market 1 said.
But there was every chance of that run breaking (as it did with November
The issue was Operation Twist, which dealt commodities three blows.
The first was in the scope of Federal Reserve's latest plan to shore up the US economy.
The US central bank had delivered "what markets expected", Paul Deane at Australia & New Zealand Bank said.
"But US equities still sold off almost 3%, indicating that while markets expected the Twist, they were hoping for more."
The second was the gloomy economic condition report which accompanied Twist, with the Fed talking of "slow" economic growth, "continuing weakness in overall labour market conditions", "elevated" inflation, a "depressed" housing sector and "weak" investment
"Moreover, there are significant downside risks to the economic outlook, including strains in global financial markets," the Fed added.
What Twist did not do was to see the Fed take on more bonds, to in effect print money, and be seen as further debasing the currency, (besides stoking inflation deemed as making commodity investments more attractive).
"Dollar length seems to like the fact that the Fed balance sheet is not going to be expanded," Brian Henry at Benson Quinn Commodities said.
The greenback indeed rose, adding 0.8% to its strongest levels since February against a basket of currencies, and making dollar-denominated assets that much more expensive.
A stronger dollar has "made it even harder for the US to compete in the export market", Mr Deane said, noting in particular the decline of the
(The real's drop since Brazil cut interest rates at the end of August has been remarkable, at 12%, and has also been seen as a big headwind to prices of other big Brazilian exports which are traded in dollars, such as
Soybeans for November fell 1.3% to $13.04 a bushel in Chicago, facing not just currency headwind, and demand fears stoked by the Fed's economic outlook, but pressure from the mounting US harvest too.
Indeed, seasonal factors suggest selling soybeans on September 22, ie today, and "buying back on Oct 2, when market typically hits its harvest lows", Benson Quinn Commodities said, noting that "harvest activity is expected to start this weekend in the northern Corn Belt".
OK, Egypt is set later to announce the results of a wheat tender which is expected to see US wheat getting more competitive with Russian grain.
"Some will view the tightening of this spread as bullish," Benson Quinn's Mr Henry said.
And there are some concerns over supplies of (high protein) spring wheat, as traded in Minneapolis, given that deliverable supplies stored in Duluth are down about 60% year on year.
"Apparently, the trade believes there is a supply issue in Minneapolis," a factor that was likely to support the exchange's December contract, Mr Henry said, while questioning the longevity of any supply squeeze.
"If spring wheat does not become more competitive with the hard red winter wheat that had better-than-average protein, the very possible end result will be lagging demand for spring wheat into the first of the year."
Minneapolis wheat certainly performed better than peers in early deals, but that meant falling less rapidly, down 0.7% at $8.35 a bushel for December delivery.
Kansas hard red winter wheat fell 1.1% to $7.52 a bushel, with lower protein Chicago soft red winter wheat shedding 1.3% to $6.58 a bushel.
The weakness was reflected in other markets too, with
As for later, besides the result of the wheat tender by Egypt, the top buyer of the grain, the US will release weekly export data expected to show soybean sales at least matching last week's 352,000 tonnes, and potentially hitting 550,000 tonnes.
The range for wheat is expected at 400,000-550,000 tonnes, compared with 413,500 tonnes last time, while the market foresees corn shipments of 550,000-800,000 tonnes, down from 1.17m tonnes.