If I were Pa Ingalls on Little House on the Prairie, and I had a ten acre field of wheat, how would I know how many wagons and horses I would need to transport the grain to the big city?

I've worked with numbers on the internet, and it looks crazy. It looks like an acre of cropland gives you 3000 pounds of grain (roughly) but that a team of two horses can only pull about 300 pounds if you drive them all day. Thus, you need 20 horses for each acre you grow. This seems crazy high to me.

Does anyone know a good resource to find reliable numbers?