Official statisticians may have overestimated the size of America's corn and soybean harvests, a leading agricultural academic has said following analysis of last week's barrage of crop reports.

Washington's assessment of an annual rise of 862m bushels (21.9m tonnes) in US corn stocks appears small against a 1.06bn-bushel increase in estimated production of the grain, University of Illinois economist Darrel Good said.

The data implied a rise of 6.5% in use of corn by US livestock farmers - a "large increase" which was "counterintuitive" given livestock sector woes and increasing competition from distiller's grains, a byproduct of bioethanol plants used as an animal feed.

"The large level of use may imply an overestimate of the 2009 crop," Mr Good said.

Seed and feed

For soybeans, the US Department of Agriculture's estimate of a 61m-bushel rise year-on-year rise in US inventories as of the beginning of December appeared small given a 322m-bushel jump in supplies.

While buoyant exports had soaked up much of the extra crop, Mr Good highlighted a doubling to 185.3m bushels in the amount of soybeans put down for seed, feed and residual use – a figure which beat the 2003 record by a margin.

"On the surface, the large disappearance suggests the 2009 crop may have been overestimated," Mr Good said, adding that details would become clearer when the US Department of Agriculture's next stocks data were released at the end of March.

'Not bode well'

Harvest doubts might offer some comfort to crop markets, which have suffered heavy declines since last week's USDA reports raised estimates for corn, soybean and wheat supplies.

However, Mr Good flagged the impact of weak economic growth and the "persistently high" unemployment rate, besides the potential for higher spring plantings on land left free by falling winter wheat sowings.

"These [economic] factors do not bode well for demand prospects for agricultural commodities for food or fuel consumption," he said.

"The lack of economic growth, along with emerging indications that Iraq could substantially increase oil production, may prevent an increase in crude oil prices that would support the biofuels industry."