Germany required like 10 percentage points more of its labor force in agriculture in 1939 than the US did, and that still wasn't enough to make Germany self-sufficient in food; the US was of course one of the major food exporters in the world (in neither case were agriculture workers more than a third of the population, I should note). US agriculture also had largely mechanized in the 1910s, albeit many farms did switch back to draft animals during the 1920s and 1930s due to the collapse in agricultural prices, making animal feed grown on your own farm cheaper than buying fuel for the tractor. Europe agriculture largely didn't mechanize until the 1950s, after WW2.