Yield potential: Its definition, measurement, and significance

Yield potential is defined as the yield of a cultivar when grown in environ ments 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 physiologic al and agronomic assumptions. Several implications of the definitions given above are considered, particularly those arising from cultivar interaction s with agronomic practices and with the biotic and abiotic environments. We then discuss both direct and indirect methods of measuring progress in yie ld potential. Continuing progress in yield potential through conventional b reeding 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 cer eals, greater field potential has derived mainly from the rise in harvest i ndex 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 o f increases in photosynthetic rapacity or maximum crop growth rate. The ris e in genetic yield potential in wheat and maize cultivars has been associat ed with progressive widening of their genetic background, and there is litt le sign of this slowing down.