By Julie Ingwersen

Benchmark Chicago corn and soybean futures climbed nearly 4% each on Monday to the highest levels in a month, as investors bought after a U.S. holiday weekend on worries about crop weather in the Midwest and Europe, and speculation about Chinese demand.

Chinese buyers bought at least five cargoes of U.S. soybeans on Monday, two U.S. trade sources with knowledge of the deals said after the market closed.

Wheat futures also rose, though prices in a Saudi tender underlined strong export competition.

Chicago Board of Trade December corn (CZ26) settled up 16-1/4 cents, or 3.7%, at $4.57-3/4 per bushel, after reaching $4.58-3/4, the contract's highest level since June 4. CBOT November soybeans (SX26) ended up 44-1/2 cents, or 3.9%, at $11.92-1/4 a bushel after hitting $11.97.

CBOT September wheat (WU26) finished 14-1/4 cents higher on the day, or 2.4%, at $6.14 a bushel.

Forecasts called for warm and mostly dry conditions across the U.S. midsection next week, fueling weather worries as the nation's corn crop begins its critical pollination stage. Over the Independence Day weekend, heavy rains swamped fields in parts of Iowa, Illinois, Wisconsin and other areas.

"There's a lot of questions as to whether we will get the corn production we were expecting this year, not only here, but in Europe," said Jack Scoville, vice president of the Price Futures Group in Chicago.

A smaller-than-expected quarterly reading of U.S. corn stocks released by the U.S. Department of Agriculture last week magnified the importance of 2026 production prospects.

Late on Monday, the USDA left its weekly condition ratings for corn unchanged at 67% good-to-excellent, but soybean ratings fell to 64% good-to-excellent, down from 65% previously, defying trade expectations for an improvement.

Meanwhile, ratings for France's maize crop hit their lowest level in 13 years after last week's record heat wave, official data showed on Friday.

Speculation about Chinese interest in U.S. crops remained a supportive factor. China's state-owned trader COFCO bought at least 300,000 metric tons of U.S. soybeans on Monday for shipment between September and November, two traders with knowledge of the deals said. The purchase volume could be even larger as more deals are finalized, the traders said.

Wheat futures followed the firm trend in corn and soy. Saudi Arabia booked 661,000 tons of optional-origin wheat in a tender, the country's state buyer said.

However, wheat export prices in Russia, the world's top supplier, continued to fall last week amid expectations of a good harvest in the Black Sea region, analysts said.