Chicago corn, soybeans jump 3% on weather risks and China demand hopes

Chicago corn and soybean futures climbed 3% on Monday as a heatwave in the United States and speculation about Chinese demand spurred buying after a U.S. holiday weekend.

Wheat also gained ground, though a firmer dollar and prices in a Saudi tender viewed as aggressive underlined strong export competition.

The most-active corn contract CBOT:ZS1! on the Chicago Board of Trade corn CBOT:ZC1! was up 3% at $4.54-3/4 a bushel by 1032 GMT.

CBOT soybeans CBOT:ZS1! also added 3% to $11.82-1/4 a bushel, while CBOT wheat CBOT:ZW1! rose 1.8% to $6.10-1/4 a bushel.

The U.S. market was closed on Friday for the Independence Day holiday.

A heatwave gripped swathes of central and eastern United States over the weekend.

While Midwest corn and soybean belts escaped the worst of the heat and are also expected to get some rainfall, the high temperatures have stirred weather worries in the run-up to crucial summer growth periods for crops.

"Now's the time for the weather market, even though it doesn't look particularly bad for U.S. crops," a European trader said.

Traders are continuing to monitor Chinese buying of U.S. soybeans and potentially other crops, after May's summit between the countries' leaders produced a pledge to expand agricultural trade.

Speculation about Chinese interest in U.S. crops re-emerged before the holiday weekend and remained a supportive factor for prices, despite a lack of indications of deals, traders said.

A lower-than-expected estimate of U.S. corn stocks in U.S. Department of Agriculture data last week also helped underpin prices after CBOT corn futures set contract lows.

The wheat market has drawn support from a surprise cut to the USDA's acreage estimate, though large harvests forecast in the Black Sea export region have tempered concerns about a small U.S. crop.

Saudi Arabia booked 661,000 metric tons of optional-origin wheat in a tender, the country's state buyer said on Monday.

Russian wheat could pick up a large share of the sales, traders said.