CHICAGO: US corn futures fell to life-of-contract lows on Monday and soybeans briefly dipped below $9 a bushel for the first time since 2016 as favorable weather outlooks bolstered yield prospects and trade tensions threatened export demand, analysts said.

Chicago Board of Trade soft red winter wheat futures also sagged and K.C. July hard red winter wheat hit a one-month low as the US winter wheat harvest expanded.

CBOT July corn settled down 5-1/4 cents at $3.56 per bushel after hitting a contract low at $3.54.

July soybeans ended up 3 cents at $9.08-1/2 a bushel, after falling to $8.97-1/4, the lowest spot price on a continuous chart since March 2016.

CBOT July wheat closed down 9-1/2 cents at $4.90 a bushel and K.C. July wheat fell 20-1/4 cents at $4.99-1/2.

Corn fell after crop-friendly rains crossed the Midwest over the weekend and forecasts called for more showers this week, offsetting concerns about high temperatures in the region.

"These rains, along with additional rainfall expected in the 6-to-10-day period, should wipe out most of the remaining soil moisture deficits across the southwestern Midwest, favoring corn and soybean crops," Radiant Solutions said in a note to clients.

After the CBOT close, the US Department of Agriculture rated 78 percent of the US corn crop in good to excellent condition, up 1 percentage point from a week earlier. The rating was among the highest for this point in the season in USDA records dating to the mid-1980s.

Analysts surveyed by Reuters on average had expected a decline of 1 percentage point.

The USDA rated 73 percent of the soybean crop as good to excellent, down from 74 percent the previous week. Analysts on average had expected no change.

CBOT soybean futures bounced after dropping sharply over the last two weeks on crop weather and trade tensions between the United States and China, the world's biggest soy importer.

US President Donald Trump last week announced hefty tariffs on $50 billion in Chinese imports, and China hit back, announcing 25 percent tariffs on 659 US goods, including soybeans, starting July 6.

Wheat tumbled on technical selling and seasonal harvest pressure as combines rolled across the southern Plains winter wheat belt.

The USDA said the US winter wheat harvest was 27 percent complete as of Sunday, ahead of the five-year average of 19 percent.

"Some people are finding a few more bushels than what they thought they had, (so) there are some sales coming to market," said Ted Seifried, analyst with Zaner Ag Hedge.