GRAINS-Corn, soy futures soar on bullish USDA plantings forecast

* USDA sees reduced corn, soy acres in 2018, surprising trade

* CBOT corn surges 3 percent, soybeans 2 percent

* USDA corn, soy stocks figures top expectations

* Wheat follows firm trend despite expected acreage growth

(New throughout; updates prices, adds quotes, changes byline, changes dateline, previous SINGAPORE/PARIS) CHICAGO, March 29 (Reuters) - U.S. corn futures jumped more than 3 percent on Thursday and soybeans surged 2 percent after the U.S. Department of Agriculture stunned traders by projecting a year-on-year decline in plantings of both crops. Chicago Board of Trade wheat futures followed the firm trend, despite the USDA's forecast of an expansion in total wheat plantings from a year ago. As of 12:58 p.m. CDT (1758 GMT), CBOT May corn was up 13 cents at $3.86-1/2 a bushel. May soybeans were up 25 cents at $10.43 a bushel and May wheat was up 6-1/4 cents at $4.51-3/4. The most-active corn contract was on track to post its biggest single-day climb since Aug. 31 after the USDA forecast U.S. corn plantings for 2018 at 88.026 million acres, down 2 percent from 2017 and below an average of trade expectations.

The government projected soybean plantings at 88.982 million acres, down 1 percent from 2017 and below a range of estimates from analysts, most of whom were expecting an increase in soybean acreage. "With both corn and soybean acres down from a year ago and expectations, it seems that the relatively poor returns for both crops (historically), along with the prospect of losing soybean business with China, has cooled expansion of total acres," said Alex Norton, analyst at Beeson Inc. The market shrugged off pressure from the USDA's larger-than-expected quarterly corn and soy stocks figures. The government reported March 1 corn stocks in all positions at 8.888 billion bushels and soybean stocks at 2.107 billion, both above most analyst estimates. "The stocks data is actually a little bit negative," said Jack Scoville, analyst at The Price Futures Group, adding, "Overall, we do have the supply; that's not changing." CBOT wheat futures followed corn and soybeans higher, despite the USDA forecasting an expansion in wheat acres. Most of the growth came in plantings for spring wheat, which the government put at 12.6 million acres, up from 11 million in 2017. The USDA reported March 1 wheat stocks at 1.494 billion bushels, in line with expectations. "Farmers still see (spring wheat) as a potential money-maker, following last year's weather-reduced crop. With wheat stocks coming in near expectations, the bigger planted area data provided some pressure to wheat markets, despite strength for corn/beans," Norton said.

CBOT prices as of 1:05 p.m. CDT (1805 GMT):

Last Net Pct Volume

change change

CBOT wheat WK8 451.75 6.25 1.4 73902 CBOT corn CK8 386.75 13.25 3.6 302503 CBOT soybeans SK8 1042.75 24.75 2.4 150414 CBOT soymeal SMK8 382.70 11.40 3.1 55623 CBOT soyoil BOK8 31.94 0.32 1.0 59563

NOTE: CBOT May wheat, corn and soybeans shown in cents per bushel, soymeal in dollars per short ton and soyoil in cents per lb.

(Additional reporting by Naveen Thukral in Singapore and Sybille de La Hamaide in Parise; editing by David Goodman and Jonathan Oatis)