So was it with Brazil rather than Russia - this US export wheat business, rumour of which supported prices in the last session?

Sure, Russia is scrapping its import duties.

But Brazil is a sizeable wheat importer, with buy-ins estimated by the US Department of Agriculture at 7.5m tonnes in 2012-13 - at a time when supplies from its default source, Argentina, have been squeezed by low sowings and rain damage to what was planted.

'Greater chances of rain'

Whatever, although the market rumour of US exports to one/both countries has yet to be confirmed for either, it afforded wheat, again, some defence against an outgoing tide in Chicago.

The March contract was down, but only 0.25 cents a pount at $7.61 ¼ a bushel as of 09:15 UK time (03:15 Chicago time) – relatively, a strong performance.

Selling was the default position on Thursday in part because of improvement in weather forecasts in South America, where corn and soybean crops have been braving excessive moisture in central Brazil, which has slowed the harvest, and overdue dryness further south and into Argentina.

"Weather models are now showing greater chances of rain in Argentina and southern Brazil in the coming weeks," Ben Bradbury at Benson Quinn Commodities said.

"Northern Brazil is seen turning drier by the weekend, which should facilitate the soybean harvest," and the planting of the follow-on, safrinha corn crop.

Wasde ahoy

And as an extra downer, there is the prospect on Friday of a USDA Wasde crop supply and demand report which is expected to increase estimates for domestic corn and wheat stocks as of the close of 2012-13, following some disappointment on exports, particularly for corn.

Extra supplies imply lower prices.

And there are other reasons to be cautious too, such as the declining technical picture.

Chicago corn for March, for instance, having already surrendered positions above its 10-, 20-, 75- and 100-day moving averages so far this month on Thursday dropped below its 50-day too, in falling 0.3% to $7.20 ¼ a bushel.

That leaves the 200-day moving average as the last major moving average the contract still remains above.

Key level

Chicago soybeans for March remain above their main moving averages, even after easing 0.5% to $14.80 ¾ a bushel.

But the trouble there is the contract's refusal, so far, to go back above the psychologically important $15.00-a-bushel mark.

"March soybeans have traded to the resistance level near $15.00 a bushel lately," said Mike Mawdsley at Iowa-based broker Market 1.

"Now the question will be is there enough news to propel us over this price range. If not, expect a sell-off, with first support near $14.70 a bushel, then $14.40."

Richard Feltes at Chicago-based RJ O'Brien, said that "price action this week is telling us that a modest 3m-4m tonne cut in Argentine soybean production potential, against a backdrop of a stable/higher Brazil soybean crop, lacks the power to push March soybeans decisively above the $15.00-a-bushel threshold.

"Markets that are unable to forge higher typically flounder."

Ags vs shares

Mr Feltes also flagged broader reasons to be cautious over gains, with agricultural commodities perhaps not the top of investors' priorities in time of an improved macroeconomic outlook.

"Hedge funds and equity traders are all not only up on the year, by 1-5%, but in addition cautiously optimistic about 2013 growth prospects and thus more willing to take on risk for higher returns. 

"What does this mean for ag commodities? It means likely diminishing participation as asset class allocators see better opportunities in other markets - especially if 2013 US weather normalises, thus triggering gains in 2014 grain stocks.

"Additionally, traders perceive better opportunities in year ahead in allocating capital to currency markets which are starting to break out of recent trading ranges."

(Agrimoney.com has in the UK, where it is based, noted a marked upswell in mention of the decline in sterling, which has lost more than 3% against the dollar so far in 2013, and twice as much against the euro – making the wheat imports it is snaffling up that much more expensive.)

Data later

Still, there is still scope for gains on Thursday, depending on what weekly US export sales data have in store.

Will they bring some confirmation of hefty wheat exports?

Traders are actually expecting a wheat figure of 200,000-500,000 tonnes, in line with the 387,900 tonnes the week before.

Corn's are pegged at 150,000-400,000 tonnes, compared with 253,300 tonnes last time, and soybean export sales at 800,000-1.3m tonnes, compared with 1.25m tonnes.

Softs harden

Many soft commodities managed a strong performance, with New York cotton for March adding 0.3% to 81.95 cents a pound, extending a late recovery in the last session.

The rebound was attributed to mill purchasing after the May contract extended a premium over the March lot, prompting some end users to play it safe and opt for cheaper spot supplies.

The May lot lost some of its advantage on Thursday, adding 0.2% to 82.69 cents a pound.

New York raw sugar for March gained too, rebounding 0.3% to 18.33 cents a pound, and looking for their first positive session in four, if still remaining close to its two-year low.

At Phillip Futures, Joyce Liu flagged the "Brazilian government's effort to bump demand for sugar by mandating a higher blend of biofuels, such as cane ethanol" in gasoline, if also highlighting a "projected lack of demand from world's sixth-largest consumer, Russia".