There were always suspicions that corn futures would struggle to hang on to its gains, given the prevailing market idea that, come frost, heat or a lower plantings number, the US crop has a large margin for downgrades before supplies look tight.
After all, the last rally, on Monday, failed to last long.
And sentiment this time was little helped, chart-wise, by the contract's surrender of its hard-won 20-day moving average at about $4.68 ½ a bushel, which the lot closed over in the last session for the first time since June, and which had provided some level of resistance selling.
That proved an indication that the huge weight of corn sellers were going to have things their way, as the bullish props which had lifted the grain in the last session eroded.
The Farm Service Agency figures appearing to show that the official US Department of Agriculture forecasts for domestic corn sowings this year is a large overestimate came under further fire, beyond that reported by Agrimoney.com overnight.
CHS Hedging cautioned that "it is not immediately known" how to what extent FSA statistics "will we passed on to the USDA balance sheet".
At broker Allendale, chief strategist Rich Nelson urged investors "not to take the FSA data at face value, flagging the poor correlation with USDA estimates.
"The FSA reduced 2m acres in 2010 on their first estimate for corn area, and in the end the USDA number dropped only 300,000 acres.
In 2011, the FSA figure signalled a 3m-acre downgrade, "and the USDA lowered its corn acreage by 400,000 from July to January".
'Risk is to the wetter side'
Concerns over dry weather eased a touch too.
Richard Feltes at RJ O'Brien highlighted "prospects for dry areas of Midwest to shrink from one-third to one-quarter of the key growing areas if Commodity Weather Group's forecast materialises for rains late next week across North Dakota, Minnesota, Wisconsin and Michigan."
"The risk is to the wetter side, with some models bringing the rains next week as far south as central Iowa and Illinois," the top two corn (and soybean) producing states.
As for signs of demand, these were not forthcoming either, after Thursday's better-than-expected US export sales data, with continued mention of South American competition.
CHS Hedging flagged reports "that China's corn imports from Argentina could grow to 1m tonnes by next year.
"China just recently approved its first 60,000-tonne purchase of genetically modified corn from Argentina."
In Brazil's favour is that the real "is falling apart", down 35% relative to the dollar in the last 18 months, Country Futures' Darrell Holaday added.
"This makes Brazilian corn and soybean exports very difficult to compete with."
Sugar displaces corn
And, domestically, the USDA dealt a blow to corn prices by revealing the sale of surplus sugar to ethanol products.
"This programme is expected to move 400,000 tonnes of surplus sugar into the ethanol market replacing 20m bushels of corn demand," Benson Quinn Commodities said, noting some ideas of even more displacement
"Some are saying government sugar stocks could replace upwards of 60m-70m bushels of corn demand by ethanol market at time the US corn supplies are increasing."
Corn for December dropped 1.9% to $4.63 ½ a bushel, although as some comfort for bulls it remained above its 10-day moving average and multi-year low of $4.45 ¾ a bushel reached earlier this week.
(As to whether it stays there next week, the results of the ProFarmer crop tour of the Midwest may have a big say.)
'Stepping up sales'
Some of these depressants applied too to soybeans, which in going through their vulnerable pod-setting process are prone, in price, to change on alterations in the Midwest weather outlook.
However, the oilseed was at least unaffected by USDA sugar plans, or by concerns over exports, for now at least.
Sure, South America is a big competitor to the US in soybean shipments too.
"South Americans, who have more old crop soybeans to sell that US, are responding to higher Chicago futures this week by stepping up sales of both 2013 and 2014 crop soybeans," Mr Feltes said.
Darrell Holaday said that "China has reportedly moved a lot of purchases for February on out to South American in the last 10 days".
'Crush margins are positive'
However, concerns were eased by the USDA's announcement of yet further sales of US soybeans to China, this time of 284,000 tonnes, with a further 126,000 sold to "unknown" suspected to be China too.
"Chinese crush margins are positive and that is why we are seeing this strong demand," one broker said.
Indeed, adding confirmed Chinese orders for 2013-14 with the 2.5m tonnes down to unknown get near to 16.5m tonnes, implying that the country's buyers have already "purchased 70% of their expected new crop purchases from the US" for 2013-14, Mr Holaday said.
The USDA has forecast exports to China of 21.6m tonnes.
Soybean futures for November fell, but by a modest 0.5% to $12.59 ¼ a bushel, rebuilding their premium over December corn futures to 2.72: 1.
Wheat sided with corn, keeping its premium of its fellow grain within sight of the $1.80-a-bushel mark, December basis, where it has appeared comfortable in recent sessions.
Benson Quinn Commodities said: "The wheat market has been mostly a follower of US row crops," besides European Union wheat prices, which eased themselves on Friday, amid improving hopes for the bloc's harvest, as highlighted on Thursday by Strategie Grains.
"A better-than-expected harvest in western EU, along with the USDA's increased global production outlook on Monday, have kept the US wheat contracts in sideways trading pattern," Benson Quinn said.
While bulls did receive a little help from a Black Earth Grain reminder of concerns over the Russian harvest, bears got ammunition from buoyant hopes for Canada's harvest.
In fact, Chicago's September contract ended down 1.0% at $6.31 a bushel, with the December lot falling 0.9% to $6.43 ½ a bushel.
Among soft commodities, the aforementioned real weakness played havoc with those in which Brazil is a big producer, cutting their value in dollar terms.
The real fell to a fresh lowest-since-March-2009 against the dollar, coming within an ace of R$2.40 to $1.
"Data showing the strengthening of the US economy have driven this trend, even with successive interventions of the Central Bank of Brazil," Brazil's Conselho Nacional do Café coffee producers' group said.
'Higher farmer selling'
In fact, arabica coffee for December dropped 0.8% to 123.30 cents a pound.
"The fall of the Brazilian real to its lowest level against the dollar since March 2009 increased the expectations of higher farmer selling in Brazil, the top grower of coffee," Joyce Liu at Phillip Futures said, also fagging pressure from "the expected high coffee output in Brazil" this year.
Raw sugar, of which Brazil is the also top producer and exporter, dropped 1.4% to 16.94 cents a pound in New York for October delivery, surrendering the technically-important 17-cents-a-pound mark.