Economists measure the influence of variety improvements, fertilizer application, regional specialization and other crop yield factors for seven major United States crops.
Auer, Ludwig W.; Heady, Earl O.; and Conklin, Frank
"Influence of "Crop Technology" on Yields,"
Iowa Farm Science: Vol. 20
, Article 6.
Available at: https://lib.dr.iastate.edu/farmscience/vol20/iss9/6