According to these calculations, putting between 263 acres (high productivity biointensive yields) and 1,660 acres (commercial equivalent yields) into production could supply 31 percent of all the fresh vegetables and 17 percent of all the fresh, non-tropical fruit that Detroiters eat each year. Increasing the seasonal availability of crops through the use of storage and season extension where possible pushes the potential portions of the produce supplied to 76 percent of vegetables and 42 percent of fruit. This would require between 568 acres (biointensive) and 3,602 acres (commercial).So high potential for food, lower number of people, or a bit of both.
From Motown to Grow-town
From Michigan State University, an enlightening analysis (PDF) of the food production potential on Detroit's vacant land - of which researchers catalogued more than 44,000 parcels covering more than 4,800 acres.