U.S. corn futures fell for the third day in a row on Wednesday as traders staked out positions ahead of a government report that was expected to boost projections for supplies of the grain at the end of the crop
year, traders said.

Chicago Board of Trade soybean futures were mixed, with old-crop contracts firming slightly on position squaring while new-crop offerings eased ahead of what is expected to be record-large U.S. plantings of the oilseed. Plunging crude oil prices kept pressure on the soy complex.

Wheat ended mostly lower, although the front-month CBOT soft red winter wheat contract edged up 1/4 cent, pressured by forecast for much-needed rains in parched areas of the U.S.

The benchmark Chicago Board of Trade May corn contract ended 3-3/4 cents lower at $3.79-1/4 a bushel, hitting a one-week low. CBOT corn has fallen 1.9 percent so far this week.

The U.S. Agriculture Department was expected to boost its 2014-15 corn ending stocks projection to 1.854 billion bushels, the most in nine years, in its monthly report on Thursday.

CBOT May wheat firmed 1/4 cent to $5.26-1/4 a bushel. KCBT May hard red winter wheat, which tracks the crop in the U.S. Plains, fell 4 cents to $5.61-1/4 while MGEX spring wheat for May delivery dropped 3 cents to $5.80-1/2 a bushel.

"Recent heat (80s to mid-90s degrees Fahrenheit/29 to 35 Celsius) eases after today in the southern Plains," Commodity Weather Group said in a research note. "Model support continues to gradually build for beneficial rains Saturday to Monday and again in the 11-to-15-day (forecast), with additional chances also in the 16-to-30-day."

CBOT May soybeans were 1/2 cent firmer at $9.71-1/2 a bushel.

Oil prices slid on Wednesday after U.S. Energy Information Administration data showed the largest weekly build in U.S. crude inventories since 2001. Record monthly output from Saudi
Arabia also weighed on the oil market.