CHICAGO, Aug 6 (Reuters) - Chicago Board of Trade wheat futures sank 1.9% on Thursday to their lowest in nearly a month, their third decline in four sessions, with expectations for rising global supplies pushing prices lower, traders said.

Corn futures steadied after hitting fresh contract lows on Tuesday, with the outlook for massive harvests in the United States keeping pressure on the market. The production forecast sparked a third straight day of losses in soybeans.

On a continuous basis, the most-active CBOT September soft red winter wheat contract hit its lowest since July 8. Front-month K.C. hard red winter wheat futures hit their lowest since Dec. 9 and MGEX spring wheat dropped to its lowest since July 2.

"Technically you are at or below contract lows," said Jim Gerlach, president of U.S. broker A/C Trading. "That has a tendency to feed on itself."

Ukrainian ProAgro consultancy on Thursday increased its 2020 wheat harvest outlook for Ukraine to 26.59 million tonnes from 26.07 million tonnes. It also bumped up its wheat export forecast for the country by 600,000 tonnes.

Canadian farmers are on track to harvest a record-large all-wheat crop due mainly to favorable crop conditions, farmer advisory service FarmLink Marketing Solutions estimated.

Early harvest reports out of North Dakota showed big yields in that state's spring wheat crop, Gerlach added.

CBOT September wheat futures were off 9-1/2 cents at $5.01-1/4 a bushel.

CBOT December corn ended up 1/2 cent at $3.23-3/4 a bushel and CBOT November soybeans were 3/4 cent lower at $8.78 a bushel.

"U.S. crops are looking very good; we are likely to see record corn and soybean production," said Phin Ziebell, agribusiness economist at National Australia Bank in Melbourne.

The U.S. Agriculture Department on Thursday morning confirmed private sales of 126,000 tonnes of U.S. soybeans to China for delivery in the 2020/21 marketing year. (Additional reporting by Naveen Thukral in Singapore and Nigel Hunt in London Editing by Subhranshu Sahu; Editing by Kirsten Donovan, Dan Grebler and David Gregorio)