Using figures of one farmer feeds X people can be misleading.
In earlier times, farmers produced their own tractors (horses) and fertilizer (manure), etc. That work moved off the farm to the factory.
I have not looked at the figures for quite some time, but if you look at yield per acre rather than per unit of labor, the US does not come out so good compared to some not very advanced countries. This deficit is not uniform, but for no major crops did the US come up on top.
-- Michael Perelman Economics Department California State University Chico, CA 95929
Tel. 530-898-5321 E-Mail michael at ecst.csuchico.edu michaelperelman.wordpress.com