It proved difficult to hang on to some of the positive spirit around earlier in the day, sparked by well-received data on Chinese factory activity.

The average commodity, as measured by the CRB index, added 0.4%, encouraged by a 0.4% drop in the dollar fostered by some idea of risk-on sentiment spurred by improved Chinese manufacturing growth,

And some agricultural commodities did even better.  

Take New York raw sugar, which rose more than 3% at one point, before losing some ground to close at 19.75 cents a pound for March, a gain of 2.1%.

But wheat, for instance, found early headway harder to hold on to.

'Expected pricing pressure'

Sugar's gains reflected the weaker dollar and also data from the Commodity Futures Trading Commission, the US regulator, showing a rise in the net short position among overall non-commercial investors, threatening a price spike if these holdings get covered.

Fundamentals are less supportive, given the unfulfilled pressure among producers to sell, said Nick Penney at Sucden Financial.

"We continue to believe that there is expected pricing pressure towards the 20 cents-a-pound area, especially from Brazilian producers given the weakness in the Brazilian real," he said.

"Thai selling is rumoured to be above that, but we feel will eventually compete with Brazil.

"We expect another test of the 19 cents-a-pound level soon, but acknowledge that in the absence of any news, the current range may be maintained for a while."

Strong exports

In Chicago, soybeans hung on to gains too, adding 1.0% to $14.53 ¾ a bushel for January delivery.

But it was hard going against soft grains, and required some upbeat ideas on US exports, and their prospects.

Weekly US export data, as measured by cargo inspections, came in at 51.1m bushels, a rise of more than 4m bushels week on week, and deemed pleasing to the trade, as were some of the breakdown statistics.

"It is interesting to note that China received 38m bushels of that total," Darrell Holaday at Country Futures said.

"Industry estimates are that China has received 410m bushels of the 587m they have purchased in the current crop year," implying plenty more buying to come.

'On a mission'

And South America hardly looks the place to buy it, with Brazilian soybean exports slumping by more than 70%, month on month, in November as supplies run dry.

Brazilian soymeal shipments slumped some 30%, and soyoil by 45%.

Besides disappointing supplies, following a drought-hit harvest earlier in the year,  availability is also being reduced by strong competition for Brazil's limited port capacity.

"The higher export prices in US are driving buyers to South America. However, shipments are now running about a two-month delay out of South American ports," Paul Georgy at Allendale said.

At broker RJ O'Brien, Richard Feltes said that "cash sources report loading times for early March Brazil soy cargoes are already approaching 55-60 days, suggesting continued brisk demand for US soybeans which are already largely committed for 2012-13.

"The soy market on a mission to slow usage which suggests penetration of $15.00 a bushel before year end - especially if next Tuesday's crop report trims US soy stocks."

The US Department of Agriculture will on Tuesday release its latest monthly Wasde crop report, a key event of the farm commodities calendar.

'Continued strong corn prices'

For corn, the dynamics were something of a contrast, with US exports for the week poor, at 9.63m bushels, down 40% week on week.

Meanwhile, November's Brazilian shipments were strong, at 3.91m tonnes, up 6.8% on the October figure.

But not all the comment was downbeat, with Darrel Good at the University of Illinois, suggesting that while the pace of US corn exports is "very low, some increase in the demand for US corn is expected yet" in 2012-13.

With Argentine weather wet, and much of the US still in drought, raising some fears over 2013 prospects, "current market conditions point to continued strong corn prices" until a much-watched report on January 11 on US crop inventories.

Big deliveries

Still, US Commodities flagged that deliveries against Chicago's expiring December futures contracts "continue to be larger than expected" for many commodities, with corn's at 246 lots.

March corn closed up 0.3% at $7.54 a bushel.

That was better that wheat could manage, weighed by deliveries of 1,939 contracts, indicating better value for producers in selling in Chicago rather than on US cash markets.

And, as an extra setback for wheat, some weather forecasts indicated rain for drought-plagued winter wheat seedlings.

'Moisture may be headed to the Plains'

There are some thoughts that some moisture may be headed to the Plains in the first half of next week," said Darrell Holaday, if being sceptical of the forecasts.

"We really do not see any significant rainfall forecast for the Plains showing up in the Plains. We do see higher prospects for the Midwest, but are not optimistic about the hard red winter wheat areas."

That was enough to wipe out the early optimism stemming from US victory at an Egyptian wheat tender for the first time in 2012-13,

"It appears the US wheat values have pulled back low enough to be competitive," US Commodities said.

Still, they pulled back a bit more for good measure, with Chicago's March contract ending down 0.4% at $8.60 ¾ a bushel.

In Paris, wheat for January edged down 0.1% to E269.25 a tonne, while London wheat for March edged all of £0.15 higher to £227.15 a tonne, helped by continued concerns for the UK's 2013 crop.