WASHINGTON — The U.S. Department of Agriculture in a special update included in its March Crop Production report reduced its estimates of 2009 corn and soybean production, although both crops remained record large.

Corn production in 2009 was estimated at 13,131 million bus, down 20 million bus from 13,151 million bus estimated by the U.S.D.A. in January, but up 1,039 million bus, or 9%, from 12,092 million bus in 2008.

The average corn yield was estimated at 164.9 bus an acre, down 0.3 bus from 165.2 bus previously, up 11 bus from 153.9 bus in 2008 and still record high. Harvested area was estimated at 79,620,000 acres, down 10,000 acres from January but up 1,050,000 acres, or 1%, from a year earlier.

The 2009 soybean crop was estimated at 3,359 million bus, down 2 million bus from 3,361 million bus estimated in January, but up 392 million bus, or 13%, from 2,967 million bus in 2008. The average soybean yield was estimated at 44 bus an acre, unchanged from January but up 4.3 bus from 2008 and the highest on record. Area for harvest was estimated at 76,372,000 acres, down 35,000 acres from January but up 1,691,000 acres, or 2%, from 2008.

“Survey respondents who reported corn acreage as not yet harvested in Illinois, Michigan, Minnesota and Wisconsin and survey respondents who reported soybean acreage as not yet harvested in Georgia, North Carolina, South Carolina and Virginia during surveys conducted in preparation for the Crop Production 2009 Summary were re-contacted in early February to determine how many of the acres were actually harvested or still intended for harvest and to record the actual production from those acres,” the U.S.D.A. said. “Respondents with unharvested corn in North Dakota and South Dakota will be interviewed at a later date.”

Corn yields in Illinois and Minnesota were lowered 1 bu an acre while yields in Michigan and Wisconsin were unchanged from January. Harvested area was reduced 10,000 acres in Michigan but was unchanged in the other states.

Soybean yields were reduced 0.5 bus an acre in South Carolina and 1 bu in Virginia but were unchanged in Georgia and North Carolina. Harvested area was reduced 20,000 acres in North Carolina, 10,000 acres in Georgia and 5,000 acres in South Carolina, with Virginia unchanged.

The U.S.D.A. noted that Dec. 1, 2009, corn and soybean stocks were adjusted by amounts comparable to production changes because unharvested production is a component of on-farm stocks.