It may be possible to have a sprayer with two separate fill sections, similar to how to how semi truck grain trailers have separate sections that can be filled with different crops. If i edit the XML to make the game think that it has two seperate sections, it should be able to be filled with two different products (ie; Herbicide & Fertilizer). Then if you use it with the chemical mixing mod, they will get "mixed" and it will let you use them together without having a separate tank on the front. I will test this on my end.