GRAINS-Corn, soybeans rise on S.American dryness; wheat firms

* Dry weather in South America raises concerns ahead of planting

* Pressure from U.S. harvest caps upside; wheat gains ground (Recasts with change in market direction; adds quote in paragraphs 3-4)

SINGAPORE, Sept 28 (Reuters) - Chicago soybeans and corn futures ticked higher on Monday, with dry weather in key producers Brazil and Argentina underpinning prices, although pressure from U.S. harvest curbed gains.

Wheat edged higher after closing lower in the last session.

“A little rain in Argentina and Brazil over the weekend is useful – where it fell. The problem regions though largely missed out on rain,” said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia.

“And temperatures remain unseasonably high, speeding evaporation of any moisture gains. Another week (of dry weather) and crop forecasters will have to start thinking about the impact of planting delays at least.”

The most-active soybean contract on the Chicago Board Of Trade (CBOT) added 0.2% to $10.00-3/4 a bushel, as of 0321 GMT, corn gained 0.1% at $3.65-1/2 a bushel and wheat rose 0.2% to $5.45-1/4 a bushel.

Still, gains were limited as U.S. harvesting of corn and soybeans speeds up and growers book sales.

Large speculators raised their net long position in CBOT corn futures in the week ended Sept. 22, regulatory data released on Friday showed.

The Commodity Futures Trading Commission’s weekly commitments of traders report also showed that non-commercial traders, a category that includes hedge funds, trimmed their net short positions in CBOT wheat and raised their net long positions in soybeans.

European association Coceral has cut its forecast of this year’s maize harvest in the European Union plus Britain to 62.8 million tonnes from 64.6 million projected a month ago, the grain trade lobby said on Friday, citing the impact of hot, dry weather.

A labour union representing Argentine grains port workers said on Sunday it would stage a 24-hour walk-off from midnight after failing to strike a deal on a collective work agreement with the business chamber that represents private port owners.

Ukraine has harvested 37.6 million tonnes of grain from 10.3 million hectares, or 67% of the sown area, Ukraine’s economy ministry said on Friday. (Reporting by Naveen Thukral; Editing by Rashmi Aich and Sherry Jacob-Phillips)