Half a million Americans moved from city to country in search of subsistence...
In Montana thousands of acres of wheat went uncut because they would not pay for the price of harvesting--sixteen bushels would earn enough to buy a four-dollar pair of shoes. In Iowa a bushel of corn was worth less than a packet of chewing gum. Apples and peaches rotted in the orchards of Oregon and California, just as cotton did in the fields of Texas and Oklahoma. Western ranchers killed their cattle and sheep because they could not pay to feed them. Yet there was hunger amid abundance. Bread lines stretched under choking grain elevators...Congressman George Huddleston [said], "I do not mean to say that they are sitting down and not getting a bite of food until they actually die, but they are living such a scrambling, precarious existence, with suffering from lack of clothing, fuel, and nourishment, until they are subject to be swept away at any time"
From the first part of the quote, it would seem that the terms of trade turned against agricultural producers. Their output could not buy much. Yet this was also the era of the Dust Bowl, which reduced supply. However, Brendon dismisses the Steinbeckian view that the Dust Bowl created the Okie migration.
Actually, the prime mover was poverty, itself the result of Depression and drought, of farm mechanisation and unemployment, of soil erosion and New Deal policies. The AAA's soil conservation and crop restriction measured fostered rural depopulation. Subsidized landlords were inclined to buy machines to do the work of men and Okies described themselves as being "tractored out" of their farms.
This is a confusing and in some ways contradictory picture. My guess is that on the whole what was going on was a transformation of American agriculture. Sharecropping and labor-intensive farming were losing out to larger farms with machinery. Land use was being reconfigured to take advantage of trucking and improved refrigeration, so that at the margin a farm near a city was less profitable and a farm located on good land farther from a city was becoming more profitable.
This transformation made food cheaper, and it greatly reduced the demand for farm labor. The displacement of farm labor broke existing patterns of specialization and trade. New patterns did not form until the 1950's. By then, more workers were urban and educated, working in distribution (including sales) rather than in primary production.