Farming is the growing of crops or keeping of animals by people for food and raw materials. Its common goals are food safety, food security and food quality. Farming is difficult due to erosion, diseases, pests, weeds, drought, rainfall and non-arable lands.
If you're referring to the farmers that attempted to farm on the plains during the 1930's, the soil became too dry and arid due to a drought as well as over-farming. To learn more about the Dust Bowl, check out: http://www.ask.com/wiki/Dust_Bowl.