Greetings Bruce:
Each state has their own guidelines and regulations when it comes to Forest Management Plans (a.k.a., Forest Stewardship Plans) -- especially if the landowner is seeking state/federal cost-share assistance and property tax relief.
Therefore, you really need to confer with your local IA-DNR district forester regarding forest management plan details. It also wouldn't hurt to contact your local district forester and ask them for some site-specific recommendations.
If you are interested in some additional resources regarding black walnut, please feel free to visit:
http://web.extension.uiuc.edu/forestry/publications/index.html
http://www.ces.purdue.edu/extmedia/fnr.htm