OK, let's just say that ADM wanted to "influence" the corn crop statistics that are gathered annually. Since the crop statistics are gathered by the local county agents office (you can look up crop statistics BY INDIVIDUAL COUNTY on the USDA site), this means that ADM would have to bribe EVERY COUNTY AGENT (not "Congressmen and Senators") in every corn-producing county in the US. And they would ALL have to be sufficiently dishonest to accept the bribe and not blow the whistle. Frankly, I don't think that scenario is of a very high probability of liklihood.
I don’t know how we got on the subject of crop statistics. Farm subsidy policy and bio-fuel subsidies are put in place by Congress with input and implementation by USDA officials.