We have information from several sources:
Nuts with Commercial Potential for America's Heartland
Exploration and Exploitation of New Fruit and Nut Germplasm—Maxine M. Thompson
Magness, J.R., G.M. Markle, C.C. Compton. 1971. Food and feed crops of the United States.
Handbook of Energy Crops—James A. Duke. 1983. unpublished.
Outside links:
Walnuts, Juglans spp. University of Georgia
Walnut Crop Information University of California Davis