What percentage of Iowa’s current row-crop farmer prosperity is the result of row-crop agriculture being completely unregulated in terms of water pollution, and therefore able to externalize water pollution costs? Installing new conventional pattern tiling, for example, raises crop yields but sends more polluted water into the drainage outlet (usually a river or lake). The farmer profits from the increased yield but pays nothing for the increased water pollution, which impacts society at large, since most rivers and lakes are public. Has any research been done on this question?