Agricultural Subsidies should impact the environment negatively (as represented in real life). Run Off, Deoxygenation, soil pollution, should boost CO2 emissions etc.
Organic farming subsidies should have lower positive impact on environment. The decrease in intensity while beneficial to the local environment, requires cutting trees down to make space for the less intensive farms.
So, there should be some modelling for deforestation and a policy to prevent food waste, which would actually have a much better positive impact on the environment than organic farming subsidies.