In Burkina Faso, grain productivity is higher in larger farms. This positive relationship goes against the dominant empirical finding known in the economic literature as the “inverse farm size-productivity relationship.” This paper analyzes the interdependence between maize and cotton production for access to fertilizer as an explanatory factor for the positive relationship. A production model inspired by Feder (1985) is applied to the production of maize under credit constraints. It states that maize yield increases with the total area of the farm, provided that this increase translates into a lifting of the cultivable cotton land constraint. The empirical validity of this model is tested using a combination of household, price, and rainfall data for Burkina Faso over the 1995–2012 period.