What do they Put on the Soil in Washington DC?

Acid fertilisers here? 

One born every minute. How many times do we have to hear this "Rescue" argument from collectors? If they are not "rescuing" looted artefacts from ISIL, its modern farming and its chemicals:

Peter Tompa‏ @Aurelius161180 14h14 hours ago Acidic fertilizers are slowly destroying coins buried in the ground so perhaps metal detecting should be viewed as salvage archaeology.

Do they have biology in US schools? The optimal pH range for the growth of most modern crop plants in the temperate zone is between 5.5 and 7.0. I am not sure what crop yield Mr Tompa thinks any farmers would expect irresponsibly placing their soil parameters much beyond that by deliberately adding acid to the soil to reduce their pH lower than they naturally are. In fact the pH of rainfall in Washington DC is currently around 4.8 to 4.9 so deliberately adding extra acid to the soil, especially in the region where he lives, would not really help feed America. 

Perhaps Mr Tompa needs to do some reading on soil science (and corrosion mechanisms) and get out and talk to local farmers about the costs of those artificial fertilisers, how they are applied to get maximum effect and lead to beneficial, rather than damaging consequences. If copper (a toxic metal) is getting into the soil water through 'acidity', that means other metals will be too, if that is the case, then that alone is cause for much more concern than whether a few coins are still in collectable condition when dug up by artefact hunters. Heavy metals in US kids' hamburgers are no laughing matter.