CHICAGO: US corn and soybean futures fell on Thursday as a firm US dollar and tumbling energy prices, with crude oil down more than 8%, stoked broad selling across commodities markets.

The steepest corn and soy declines in more than a week marked a further pullback from recent highs as improving crop weather in South America and expectations for large US planting increases this spring weighed on prices.

The bearish factors overshadowed stronger-than-expected weekly corn export sales and confirmation from the US Department of Agriculture (USDA) of large corn sales to China for a third straight day.

"The improvement in rains, especially in Argentina, is weighing on the trade so prices are backing off of multi-year highs," said Terry Reilly, senior commodities analyst with Futures International.

"The only bright side I see is the weekly export sales above expectations in corn.

We already know what might be pencilled in for next week's report so it's buy the rumour, sell the fact today," he said.

The USDA has confirmed US corn sales to China totalling nearly 3.1 million tonnes over the past three days, along with weekly sales of 1.23 million tonnes in the week ended March 11, topping trade expectations.

Chicago Board of Trade May corn fell 11-1/2 cents to $5.46-1/2 a bushel, while May soybeans dropped 25-1/2 cents to $13.92-1/4.

CBOT May wheat fell 9-1/2 cents to $6.30-1/2 a bushel, a six-week low.

Grain markets have been under pressure this week as crop weather improved in South America following recent dryness in Argentina and excessive rains in key parts of Brazil.

Rain storms this week in Argentina's Pampas farm belt have slowed the deterioration of many drought-hit soybean and corn fields, crop weather specialists said.

Grain traders are monitoring news from a meeting between high-level US and Chinese officials on Thursday.