SCOTUS And WOTUS
The Supreme Court is about to hear a case from Hawaii that will involve many of the discussions about point source pollution, some of which could affect farmers with field tiles.
See this University of Illinois review of a number of cases all of which are likely to be considered by the Supreme Court in their Hawaii deliberations and read the discussion of how they may apply to your situation.
It ain't pretty, is my take on it.
Re: SCOTUS And WOTUS
Have to hope that the intent of the producers would be considered .. assuming the intent of tiling in the first place is to keep moisture and nutrients in the field at full saturation levels. What water is released by tiling has undergone at least 6 feet of soil filtration.
Secondly The comparison to run off water from surface only (without tile) is not going to compare favorably with tile runoff water, because the surface water loss will contain far more applied fertilizer and chemicals plus whatever dust, chemicals and smogish debri is gathered from the air and atmosphere created by urban combustion and natural wind and storm activity.
IMO the process of tiling works in conjunction with our natural air cleaning process of precipitation to take pollutants out of the air and water. Unfortunately it does not do much to fix urban budgets.