* Swift planting, rainfall boost U.S. corn harvest outlook * Corn underpinned by China demand, Brazil yield losses * Wheat steadies after 1-month low * Soybeans stabilise after 3-week low * Market weighs wheat crop weather, volatile veg oil prices (Updates with European trading, changes byline/dateline) By Gus Trompiz and Naveen Thukral PARIS/SINGAPORE, May 25 (Reuters) - Chicago corn prices edged lower for a third straight day on Tuesday as favourable U.S. growing conditions offset recent support from Chinese demand and drought in Brazilian corn belts. Soybeans ticked up, steadying after a five-session fall, with support from a rebound in vegetable oil prices. Wheat also recovered slightly after hitting a one-month low on Monday, as a decline in U.S. winter wheat crop ratings tempered optimism about the benefit of recent rainfall in the U.S. Plains. The most-active corn contract on the Chicago Board Of Trade (CBOT) was down 0.2% at $6.56 a bushel by 1210 GMT. In a weekly update issued after Monday"s market close, the U.S. Department of Agriculture (USDA) said farmers had planted 90% of intended corn acres as of Sunday, above the five-year average of 80% and just below an average estimate of 91% in a pre-report Reuters poll. "The figures on U.S. planting progress continue to leave little room for doubt and are pressuring prices today," a European trader said. Brisk planting, coupled with regular rain in the U.S. Midwest, has taken attention away from global supply tensions, although cool spring temperatures have raised some question marks. Higher than expected USDA supply projections for 2021/22 earlier this month and steps by China to rein in prices of commodities including corn have also curbed futures after multi-year peaks. But some analysts see limited downside for grain prices. "We think the underlying supply-and-demand fundamentals are still tightening. We are more likely to see strong rallies over the next few months, rather than large drop in prices," said Ole Houe, director of advisory services at brokerage IKON Commodities in Sydney. CBOT soybeans were up 0.9% at $15.36 a bushel, after touching their lowest since April 30 on Monday. A 3.5% rebound in palm oil futures supported soybeans as tight edible oil supply remained a focus of oilseed markets. U.S. soybean planting remained ahead of the average pace of recent years, although was a touch below analyst expectations, the USDA data showed. CBOT wheat was up 0.5% at $6.65-3/4 a bushel, having hit its weakest since April 20 in the last session. Prices at 1210 GMT Last Change Pct End Ytd Pct Move 2020 Move CBOT wheat 665.75 3.50 0.53 640.50 3.94 CBOT corn 656.00 -1.25 -0.19 484.00 35.54 CBOT soy 1536.00 13.25 0.87 1311.00 17.16 Paris wheat Sep 209.50 1.25 0.60 192.50 8.83 Paris maize Jun 255.00 0.75 0.29 198.75 28.30 Paris rape Aug 518.00 5.00 0.97 393.00 31.81 WTI crude oil 65.82 -0.23 -0.35 48.52 35.66 Euro/dlr 1.23 0.00 0.37 1.2100 1.32 Most active contracts - Wheat, corn and soy US cents/bushel, Paris futures in euros per tonne (Reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore, Editing by Sherry Jacob-Phillips and Emelia Sithole-Matarise) Our Standards: The Thomson Reuters Trust Principles.