Deductions & credits

I live in Iowa but sold some property in ND a few years ago.  There were capital gain on the sale (property held for more than 10 years before sale).  Do I declare the gains on my Iowa state form or on the ND form?  Or is it my choice?  I file a ND form each year because I receive some interest payments each year.  Or can both the gains and interest be declared on my Iowa form?