Next step, make it legally required to apply the additive. Like filters in chimneys, catalytic converters in cars, etc. and have fines attached to not using it.

If that doesn’t work, increase fines and/or add criminal charges and prison.

Why not put the additive in the feed at the factory that produces it?

You mean... a field? I get that farming has gotten industrial, but there's not like, a "alfalfa factory" out there pumping out silage.

Enforcing laws on farms is challenging, often to the point of futility, and particularly when you’re talking about large-scale ranches.