Yield potential: Its definition, measurement, and significance

Yield potential is defined as the yield of a cultivar when grown in environments to which it is adapted, with nutrients and water nonlimiting and with pests, diseases, weeds, lodging, and other stresses effectively controlled. As such, it is distinguished from potential yield which we define here as the maximum yield which could be reached by a crop in given environments, as determined, for example, by simulation models with plausible physiological and agronomic assumptions. Several implications of the definitions given above are considered, particularly those arising from cultivar interactions with agronomic practices and with the biotic and abiotic environments. We then discuss both direct and indirect methods of measuring progress in yield potential. Continuing progress in yield potential through conventional breeding is apparent in many crops, and is significant for yield progress at the farm level under a wide range of conditions. Among the small grain cereals, greater field potential has derived mainly from the rise in harvest index associated with dwarfing, whereas in maize (Zea mays L.), it has come from increased tolerance to closer planting. The duration of photosynthetic activity has been extended in several crops but there is little evidence of increases in photosynthetic rapacity or maximum crop growth rate. The rise in genetic yield potential in wheat and maize cultivars has been associated with progressive widening of their genetic background, and there is little sign of this slowing down.