Are agricultural facilities potentially subject to the risk management program requirements in 40 CFR Part 68?

Yes. Although there is one specific exemption from the provisions of 40 CFR Part 68 for ammonia held by a farmer for use as an agricultural nutrient (40 CFR §68.125), there is no general exemption from the risk management program regulations for farms. If fertilizers, pesticides, or any other materials present at a farm are (or contain) regulated substances in excess of the applicable threshold quantity, the facility must comply with the requirements in 40 CFR Part 68. Ammonia held for distribution at a farm would not be exempt. In addition, even if a farmer is exempt from the Risk Management Plan rule, he is still subject to the General Duty Clause under CAA §112(r)(1).