Farm subsidies and flooding

I'd like to build on my earlier post about how to build and retain topsoil for a bit here. If indeed the amount of organic matter in topsoil is primarily a function of how many dead plant roots are in there, and plowing the ground tends to reduce topsoil by allowing this organic matter to decay more quickly (plowing introduces oxygen), what then is the result of farm subsidies with regards to flooding?

Well, if, as Nixon's agricultural advisor noted, a goal of subsidies was to get farmers to plow "fencerow to fencerow," we would assume that subsidies would reduce the ability of soil to hold water by encouraging topsoil destruction, and would then result in flooding far worse than would otherwise be the case.

Is it possible that the reduction of Iowa topsoil from 14" thick on the average to 5" thick on the average was a significant contributor to the devastating flooding that state experienced this year? It would also be interesting to measure (if that's possible) the amount of carbon dioxide emitted as newly plowed fields have their topsoil literally rotting away.

Isn't that awesome? We get to pay tens of billions of dollars in subsidies each year to, in part, cause tens of billions of dollars of flood damage in agricultural states. What a deal.