Using selective maize yield data from ethnohistoric and government sources dating between the mid-nineteenth and mid-twentieth centuries, Schroeder (1999) argues that Mississippian average yield potential fell within a 9-10 bu/acre range. We evaluate her argument in terms of well-established climatic, environmental, varietal, and behavioral constraints on maize agriculture and conclude that reconstructing prehistoric agricultural potential requires a more precise methodology that incorporates these factors.