What caused the crash of the cash flow needed to support all that? 

Grain embargo. 

I think corn dropped from 2.75 or 2.60 down to a low of 1.80, maybe lower.  It stayed that way for 4 or 5 years from 1980 to 1985.   

Also there was inflation.  Not just 2.5 to 3 % inflation we have today, but inflation of 6 to 10%.  

The Great Grain Robbery started it all of in the late summer or fall of 1972.  Dec. corn went from about 1.50 to about 2.40.  

I remember the farm just to the south of Dad's property came up for sale.  $87,000 for 160 acres.  Some pasture, mostly irrigated land.  I showed Dad on paper that he could buy the land with 20% down and rent it out and it would be paid for in 20 years.  He did not have to work the land, nor buy a pivot, ect.  Just rent it out at average rental price.  This was before corn went up.  Was for sale in the spring of 1972.  Nope.