Grains eventually got round to following the script that many investors had prepared for them, of a soft finish to the week, but it meant ignoring a broadly positive close in other markets.

Many risk assets took heart in much-anticipated comments from Ben Bernanke, the Federal Reserve chairman, who said that the US central bank would ease monetary policy "as needed", while backing as "effective… non-traditional policy measures", code for quantitative easing.

Wall Street stocks were 0.8% higher in late deals, while the dollar tumbled 0.6% for fears of debasement by monetary easing.

A softer greenback supports prices of dollar-denominated exports, including commodities, by making them more affordable to buyers in other currencies.

Softs harden

And indeed, the CRB commodities index added 1.0%, helped by 1.8% rise in Brent crude to $118.70 a barrel in late deals.

Many soft commodities managed just about to surf the wave, with New York December cocoa adding 0.3% to $2,610 a tonne, sure, not a huge jump, but one which lifted the bean to it highest finish, for a nearest-but-one contract, for nine months,

Worsening prospects for production in the Ivory Coast crop, the world's biggest, where cool weather is hurting yield hopes, added to upbeat mood.

And even raw sugar managed gains, adding 0.2% to 19.78 cents a pound for October delivery, despite the International Sugar Organization calling time on a four-season period of tight supplies and cautioning over "bearish pressure on prices".

New buying next week?

That said, the prospect of the end of the month, typically a period when funds close some positions, and a long weekend, which also tempts investors to take profits, was supportive of sugar values, given that it is short positions which have been in vogue in the last few weeks.

For grains and oilseeds, in which funds have been piling on long exposure, this dynamic worked in the opposite direction, one reason many had forecast a soft lead into the US Labor Day weekend.

OK, there is some expectation that this would only prove temporary.

"The floor is looking for new buying to show up next week in the entire complex," Mike O'Dea at broker FCStone said.

However, Friday barely felt like a day to jump in when a glance at history rang alarm bells.

"On August 29 last year, a top was put in on soybeans. We made a contract high yesterday in the November soybean contract," Allendale president Paul Georgy said.

'Probably surprised the market'

And there were some more current negative developments around which bears could make a decent case.

One was Russia's declaration that it would not impose grain export curbs, despite looking at a wheat harvest, on SovEcon estimates, more than 2m tonnes lower than the 2010 result which prompted a full ban on shipments.

"The Russian announcement has provided the most selling pressure in wheat and that has bled into the corn market," Darrell Holaday at Country Futures said.

"This probably surprised the market given the 38m-tonne production estimate."

Furthermore, for Western Australia, the country's top grain-growing state where dryness is threatening crops,  "the six-to-10 day weather outlook is a little wetter and that is adding to some of the selling pressure in wheat", Mr Holaday said

'Profit-taking has developed'

Another negative came from technical analysis, with Chicago's December corn and wheat contracts falling decidedly back under their 20-day moving averages.

In soybeans, "profit-taking has developed as the market was not able to challenge yesterday's contract after settling on a weak note yesterday", again seen as a chart setback, Benson Quinn Commodities said.

Indeed, foreseeing early on that "perhaps the order of the day will be profit-taking ahead of the weekend", it said that "price action is hinting that poor yields have been factored in to a large extent, which makes sense at $8.00-a-bushel corn and $17.50-a-bushel soybeans.

"While demand will have to be rationed, the impending shortage of US corn and soybeans is not a current issue as harvest progresses."

Brazil corn lands in US

Meanwhile, Friday also brought another reminder of the weak competitiveness of US corn exports, with reports that the first load of the grain purchased from Brazil, by feeds users desperate for competitively priced ingredients, is unloading on the US east coast.

This after another week of poor export sales data, released on Thursday.

OK, traders continue to applaud soybean shipments

"Export sales are at 58% of the US Department of Agriculture export goals for 2012-13, versus 27% on average," US Commodities noted.

Also deliveries against expiring September contracts came in at zero for corn, soybeans and Kansas wheat, a signal of better values in cash markets, while 334 contracts of Chicago wheat were delivery, and 56 oats.

And wheat gained a snippet of support from an official German harvest estimate a little below that of private consultants, and acknowledging some disappointing protein results in a harvest "satisfactory" on quality overall.

Prices fall

However, it was not enough to shrug off that month-off selling feeling to send  Chicago soybeans down 0.6% to $17.56 ½ a bushel for November delivery.

December corn lost 1.1% to $7.99 ¾ a bushel, while December wheat, feeling the extra pressure of deliveries and Russia's decision, dropped 1.8% to $8.89 ½ a bushel.

Earlier, Paris wheat for November closed down 1.1% at E263.75 a tonne.

London's November contract ended down 0.6% at £204.85 a tonne, getting some support from the dismal state of the UK harvest, which on one quality measure is the worst for at least 36 years, and the restarting of the Ensus bioethanol plant, taking up to 5,000 tonnes of wheat a day.