After reading some great excerpts from old agriculture books, I've decided to collect as many as I can find that are pre-1940. I found some very promising ones at the Antique Mall in Barnesville.
Agriculture Yearbook, 1924. Topics include hay, poultry, and weather, as well as the agricultural statistics for the year.
Yearbook of Agriculture, 1935. Includes the previous year of agriculture, new developments, and statistics.
Yearbook of Agriculture, 1936. Topic: Genetics and the improvement of plants and animals. No statistics, because this was the first year that they were moved to their own volume.
Pork Production, by William W. Smith. 1937. Extensive information on all phases of pork production, including several chapters on forage and several more on feeding other agricultural by-products (skim milk, whey, etc).
Old McDonald Had A Farm, by Angus McDonald. 1942. This one is actually a biography, but I couldn't resist after reading the author's note at the beginning.
"This book is about my father, James Angus McDonald, and how he labored to make a good farm out of a poor one. I lived on this farm with him and my brother, sister, and mother from 1912 to 1922, near Sallisaw, Oklahoma."
I have no idea if it will be any good, but there might be some agricultural gems hidden in the prose.
There was also a cardboard box filled with herd registry books for the American Jersey Cattle Club from the 1890s. The entire box was $50 and I was really tempted to buy it, just because I like poring over that sort of thing. Plus, if I ever get into full-sized dairy cattle, Jerseys are probably what I would get. I managed to restrain myself, although if the box is still there next time I go down there, I may not be able to resist again. Other than the registry books, I pretty much cleaned them out of agriculture books.