Besides economics, there's the environment. The "ideal conditions" mentioned earlier are rare. No matter how it's done, plowing is a questionable activity in a dry climate like Ingre's: nothing is more efficient for removing valuable humidity from the soil. Oxen plow before it rains (so the farmer only loses topsoil to the wind), but there's no advantage using horses when the ground is dry and hard, or wet and muddy. In my experience, they're actually slower.

My second year in Imi I started investigating cover-crops and direct-seeding methods. Working with the horses (though it was only once in a while) was a distraction from more important activities.

(In this picture they're transporting sugarcane. I'm including it because I like the action, but I'm embarrassed by how skinny the horses --especially Pochi-- look. In mid-winter there just isn't very much for them to eat; I learned that giving them corn was important for keeping them healthy, but that it was no substitute for letting them browse a well-stocked forest or pasture, in summer.)