Newt Gingrich earned some $600,000 as a consultant to a major ethanol lobbying group, not the $312,500 that the organization, called Growth Energy, disclosed last spring.

When quizzed by iWatch News in April, Growth Energy spokesman Chris Thorne said Gingrich’s contract ended after 2009. Attributing the mistake to an internal miscommunication, Thorne now says that Gingrich remained on the payroll through 2010 and earned an additional $262,500.

Thorne said that Gingrich continued to work for Growth Energy  for the first few months of 2011 as well, but he could not say how much the former Speaker was paid.

Growth Energy was founded in late 2008 by the world’s top ethanol producer — the South Dakota based POET group — and other fuel companies to promote the use of the alternative fuel. According to the company’s Web site, Gingrich was paid to offer advice on “strategy and communication issues” and to “speak positively on ethanol related topics to the media.”

Gingrich’s ties to the industry have been a boon, no doubt, to his presidential campaign in a farm state like Iowa. But his embrace of federal ethanol subsidies has irritated some conservatives, who believe that government intervention in the economy violates free-market principles.

Gingrich got into a well-publicized spat with the editorial page editors of the Wall Street Journal — they called him “Professor Cornpone” — a year ago, compelling him to declare, “I am not a lobbyist for ethanol.”

A Gingrich campaign spokesman declined to comment on the recalculated totals, which were disclosed in a recent story in USA Today.