Se refiere al polvo que se levanta facilmente con viento luego de las operaciones de labranza tradicional, especialmente las de baja profundidad como el uso de la grada/rastra. En Wikipedia también citan la obra de Steinbeck, en relación al polvo.

Referencia:
"Overuse of disc harrows in the High Plains of the United States in the early 20th century may have contributed to the "Dust Bowl". "
https://en.wikipedia.org/wiki/Disc_harrow

"The Dust Bowl was a period of severe dust storms that greatly damaged the ecology and agriculture of the American and Canadian prairies during the 1930s. The phenomenon was caused by a combination of both natural factors (severe drought) and manmade factors (a failure to apply dryland farming methods to prevent wind erosion, most notably the destruction of the natural topsoil by settlers in the region)"
...
"The Dust Bowl has been the subject of many cultural works, notably the novel The Grapes of Wrath (1939) by John Steinbeck"
https://en.wikipedia.org/wiki/Dust_Bowl