Sioux County in northwest Iowa was the top corn yield producer for the 2010 harvest, coming in at 196.5 bushels per acre, according to county-by-county figures released Tuesday by the U.S. Department of Agriculture.

Sioux’s production was still down from 203 bushels per acre in 2009, reflecting the damage done to Iowa crops by the record rainfall in July. Statewide the yield average dropped from 182 bushels per acre in 2009 to 165 bushels per acre in 2010 and total production fell from 2.42 billion bushels in 2009 to 2.15 billion bushels last year.

The reduced corn yields have played a significant role in the narrowing of U.S. domestic corn stocks from 1.8 billion bushels last May to around 700 million bushels by early 2011, which in turn has helped push corn prices up from $3.50 per bushel in June of last year to $7.25 per bushel in futures markets this week.

The top soybean producing county in Iowa last year was Marshall County, with 57.4 bushels per acre. The state average of 51 bushels per acre in 2010 was unchanged from the previous year.

The damage from the July rains was heaviest to corn yields in south central Iowa. Appanoose saw its 2009 average of 154 bushels per acre drop to 75 bushels per acre in 2010. Wayne County’s 144 bushel per acre average from 2009 dropped to 73 bushels last year, the lowest average among Iowa’s 99 counties.

Northeast Iowa escaped the July rain damage and actually increased yields in 2010. Howard and Winishiek counties saw 20-bushel per acre average gains to 191 and 190 bushels per acre respectively.

No Iowa county averaged more than  200 bushels per acre for corn in 2010, as Sioux, Plymouth, Cherokee, Carroll, Crawford and Shelby did in 2009. Shelby saw its yields drop more than 30 bushels per acre to 171.6 bushels due to rains and some flooding along the notorious West Nishnobotna River last last July.

Soybean yields were more consistent. Joining Marshall at 56 bushels per acre or more last year were Sioux at 57 bushels, Clayton at 56.8 bushels, Delaware at 56.3 bushels and Crawford at 57 bushels.

Iowa total soybean production for 2010 increased to 496.2 million bushels compared to 486 million bushels in 2009.

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