Production functions of one type or another have been well explored and widely discussed, no less in the literature of agricultural economics than elsewhere. A particularly fruitful area of application in farm economics is the quantification of the relationship between fertilizer inputs and crop output. In this context currently in Australia and New Zealand, more than passing interest is being devoted to problems of experimental design and subsequent interpretation of results. (1) Another problem area relates to the choice of the most appropriate type of function to use. This note examines possible relevant functions for crop fertilization experiments. Subsequently, a set of empirical data are fitted and the derivation of the more elementary economic optima are demonstrated.