As Tyler notes:
Multi-factor productivity in agriculture skyrockets in the mid-1930s, not earlier.
Yes, there was a fall in demand. Yes, there was the dust bowl. But all those unemployed were not from solely those two: there was also a massive structural change going on.
The replacement of the horse and mule with the first really viable tractors simply meant that there were fewer jobs available. Lots of people simply had to go and find something else to do.
Analagous to what happened to the industrial North of the UK in more recent decades. Then and there it was the productivity of labour in agriculture that soared, for us it was the productivity of labour in manufaturing.
Huge, wrenching, changes thus ensue and no, there isn\’t a Keynesian solution to such. Hayek perhaps, but not Keynes.