Soybean and wheat prices were also lower.

The most-active corn contract on the Chicago Board Of Trade was down 1.3% at $4.30 a bushel by 1120 GMT, having gained 1.4% in the previous session.

Dealers said temperatures were cooling in the US Midwest after storms and extreme heat over the weekend threatened to curb US corn yields.

"The size of the US corn crop remains 'in play' so the market is unlikely to truly settle," said Tobin Gorey, director of agricultural strategy, Commonwealth Bank of Australia.

"The US Midwest has enough areas that might quickly develop crop issues to keep the market on its toes."

Large speculators raised their net long position in CBOT corn futures in the week to July 16, regulatory data released on Friday showed.

The CBOT's most active soybean contract fell 0.5% to $9.14-1/4 a bushel.

Dealers said signs that trade tensions between the US and China may be easing helped to underpin soybean prices.

"Grain markets are headline watching as US-China trade talks show signs of progress," brokerage Allendale said in a market note.

US President Donald Trump said on Friday that US Treasury Secretary Steve Mnuchin had a very good talk with his Chinese counterpart, amid signals from China that officials could soon meet face-to-face in their bid to end a yearlong trade war.

The CBOT's most active wheat contract fell 0.9% to $4.98 a bushel while December milling wheat on Paris-based Euronext was down 0.8% at 180 euros a tonne.

The wheat market is facing pressure as rapidly advancing harvest across the northern hemisphere boosts global supplies.

The European Union is set for a larger wheat harvest this summer as a heatwave in late June which wilted some crops had a less severe impact than initially feared, traders and industry officials said on Friday/