Explanations for Yield Improvement in New Vs. Old Soybean Cultivars.

ABSTRACT Reasons for the gradual genetic yield improvement (21-31 kg ha-1yr-1) for soybean during decades of cultivar development are not clearly understood. Identification of causative factors for the yield improvement would aid in providing indirect selection criteria for streamlining cultivar development. Our objective was to identify yield components, growth parameters, phenological data, and/or other agronomic data responsible for yield improvement in 18 cultivars released between 1952 and 2000. Results indicated that yield improvement was related more to increased dry matter accumulation than to greater Harvest Index. Yield enhancement in new vs. old cultivars was mainly related to greater seed, pod, and node numbers per area. In conclusion, genetic yield improvement was related to increased dry matter resulting in greater production of nodes, which in turn stimulated pod and seed numbers.