Here is an interesting Fordson manual from 1920. This was before Henry bought out his minority stockholders in the Ford Company. Fordson was owned by Henry and Edsel.
I've started reading Michael Pollan's book, "The Omnivore's Dilemma," and it's about corn right now, and how the average was 20 bushels per acre in 1920, about the same as 400 years ago, and there were only 225 tractors in the US that year.
Has anybody seen different figures on tractor population in 1920? It has to have been in the hundreds, if not thousands.
Oh, there had to be more than that. You had Fordson, Case, John Deere/Waterloo, Hart Parr, Rumely, Twin Cities, & Minneapolis and that just scratches the surface. Mind you, this was before row-crop versions had evolved.
20 bushels an acre for corn sounds about right. This was before the widespread use of hybrids which increased yields considerably even before the use of chemical fertilizers. What I DO wonder is if those bushels were shell corn or cob corn? Shelling was a separate operation and a lot of corn at the time was used in cob form as animal feed.
I know nothing about the book you mentioned but it would be interesting to see if there is any mention of the sources of his information. Agriculture Department and Census Bureau information would be the best sources, I'd guess.
Henry Ford had built more than 158,000 Fordson Model F tractors from 1917 until the end of 1920. So there were way more than 225 tractors in operation. There were scores of other companies building tractors at this time.
If you are interested below is a link to a Fordson serial number page showing production each year.