The potential and actual primary productivity of southern Ontario's agro-ecosystem

There is a generally accepted assumption that the primary productivity of the natural vegetation cover of an area is the most appropriate indicator of the level of primary productivity that may be attained by agricultural systems in the same area. However, this relationship is not clearly understood. This paper assesses the potential rate of primary productivity for southern Ontario and compares these results with the equivalent values for the agro-ecosystems. Analysis is conducted at the level of the county. Climatically determined potential (natural) primary productivity values are adjusted by a soil performance index yielding a range of values from 986 g m^?2 y^?1 to 44 g m^?2 y^?1. The actual primary productivity for agriculture ranges from 3593 g m^?2 y^?1 to 515 g m^?2 y^?1. Over southern Ontario actual (agricultural) productivity exceeds potential (natural) productivity by an average of 2.6. The variations about this mean are examined. The results indicate where, and by which agricultural processes, the humanized landscape can improve the organic resource base.