I was chatting with the owner of a local farm of which I am a subscriber, and he mentioned that he was considering hauling boxes of veggies between work sites using a bicycle or tricycle. There is of course variety of cargo bikes and trailers in the world to choose from, but most utility bicycle equipment is oriented towards paved surfaces. Thus trailers with 20-inch wheels might not fair so well on unimproved trails. 

Are there styles of bike, trike, or trailer that are already in use on farms that you've seen or heard of? How much trail improvement should he undertake, since his roads are mostly driven by his tractor and delivery van?