Soybean yield potential - A genetic and physiological perspective

Soybean [Glycine max (L.) Merr,] yields in the USA have risen 22.6 kg ha(=1 ) yr(-1) from 1924 to 1997, but in the last quarter century (1972-1997) hav e risen 40% faster, 31.4 kg ha(-1) yr(-1) This upward trend in on-farm yiel d is fueled by rapid producer adoption of technologies emerging from agricu ltural research. Published estimates of the annual gain in yield attributab le to genetic improvement averaged about 15 kg ha(-1) yr(-1) prior to the 1 980s, but is now averaging about 30 kg ha(-1) yr(-1) in both the public and proprietary sectors. Periodic advances in agronomic technology, and a rele ntless rise in atmospheric CO2 (currently 1.5 mu L L-1 yr(-1)), also contri bute to the upward trend in on-farm yield, In Nebraska, irrigated yield ave rages 800 kg ha(-1) more than rainfed yield, and is improving at a 40% fast er annual rate (35.1 vs. 24.9 kg ha(-1)), About 36% of the annual variation in the irrigated-rainfed yield difference is attributable to annual variat ion in absolute rainfed yield. Inadequate water obviously limits absolute c rop yield, but also seems to be an obstacle in terms of the rate of yield i mprovement. Several physiological traits changed during sis decades of cult ivar releases in Ontario that led to a genetic gain in yield of about 0.5% yr(-1). Changes in some traits were obvious (improved lodging), but more su btle in others (greater N-2-fixation, greater stress tolerance). In terms o f photosynthate supplied to sinks across a wide range of environments, rece nt cultivars seem to be superior to obsolete ones. To sustain and enhance s oybean yield improvement in the future, technological innovation must be co ntinually injected into the agricultural enterprise.