So much for the seasonal fears of a collapse in agricultural commodities.

After grains suffered a sharp decline last year from a late-August peak, many investors have been fearing a repeat this time.

Harvest pressure, as the uptick in supplies shifts power temporarily to buyers, has only the added to the sense of caution.

"Seasonal charts point to grain and oilseed weakness, "Rory Deverell at broker FCStone said.

"But is this the year to buck the trend?"

'New buying in the entire complex'

In early deals on Tuesday, it was looking that way, with Chicago soybeans returning from a long weekend, after Monday's US Labor Day holiday, to set a fresh record for a spot contract (currently September) of $17.94 ¾ a bushel.

The best-traded November lot hit a contract high of $17.89 a bushel, before easing as of 09:00 UK time (03:00 Chicago time) to $17.81 ¼ a bushel, up 1.4% on the day.

And there were some reasons for bulls to think they may get the upper hand, with one calendar pressure pointing their way – it being the first trading day of the month.

This is, by repute, a time when funds often introduce fresh cash, with month end seen as a period of removal.

On Friday, futures indeed faded. And at the time, FCStone's Mike O'Dea noted that the "floor is looking for new buying to show up next week in the entire complex".

Brazil running dry?

There were some fundamental reasons to buy soybeans too, one being official data from Brazil showing a slump in shipments to 1.96m tonnes for the first four weeks of August, from 4.13m tonnes in July.

This implies yet more demand for US soybeans, if supplies from Brazil, the second ranked exporter (and expected to take top spot in 2012-13) are running dry.

And this when there are pressures delaying the imminent US harvest, one being the forwardness of the backward US corn crop, which means many farmers are combining the grain first rather than the oilseed as normal.

Some observers, such as Jerry Gidel at Rice Dairy, have also cautioned over the impact of last month's Midwest rains in, while boosting soybean yield potential, delaying the harvesting date while pods fill out.

'Weak, short-lived El Nino'

As a further prop to bulls, New Zealand meteorologists added to the caution surrounding the El Nino, which Agrimoney.com highlighted last week.

This year has long been expected to bring an El Nino, which typically follows back-to-back La Ninas as seen the past two years.

And an El Nino is seen as largely good news for Brazilian soybean growers, in typically bringing plentiful rains, and viewed by many as helpful to the US Midwest too, being linked to cooler summer temperatures.

However, New Zealand meteorologists on Tuesday said that "borderline El Nino conditions are present in the tropical Pacific, and a weak, short-lived El Nino is predicted for the spring and summer periods".

The weather event would likely "decay" in the first quarter of 2013.

'Rains were big'

Corn took heart in soybeans' rise, potentially getting a boost from early-month money too.

But it faced the pressure of rising Brazilian corn exports, up 200,000 tonnes at 1.9m tonnes month on month in August, as expected when the country enjoyed such as strong safrinha crop harvested within the past couple of months.

Chicago's December contract added 0.9% to $8.07 a bushel.

Wheat rose in line, up 0.9% at $8.97 ¼ a bushel for December, feeling itself some pressure from decent rains over the weekend in parts of the Midwest, which while too late for row crops (in fact, only likely to have delayed harvest) will moisten seedbeds for (largely soft red) winter wheat.

"Isaac rains over the past three days in the eastern Corn Belt were big," WxRisk.com said.

Thai downgrade

Elsewhere, New York raw sugar got off to a decent start too, adding 0.4% to 19.86 cents a pound for the October contract, helped by slightly lowered forecasts for Thailand's output.

Thailand's Office of Cane and Sugar Board forecast that sugar output from the world's second-ranked exporter of the sweetener "could be slightly lower than we forecast earlier".

The initial estimate was 10.2m-10.4m tonnes.

But, in Kuala Lumpur, palm oil dropped 0.5% to 3,057 ringgit a tonne for November delivery, pressed in part by fears of heightened Indonesian competition, to Malaysia, in export markets.

However, El Nino is seen as a negative to palm oil output, bringing dry weather to both countries. A weaker El Nino would, thus, ease production fears.