Physiological Processes Leading to Similar Yield in Contrasting Soybean Maturity Groups

Soybean [Glycine max (L.) Merr.] maturity groups (MGs) exhibit large variation in time to maturity, and are adapted to different latitudes. There is a range of MGs that have similar yield potential at most production regions, especially at temperate and tropical environments. We tested whether similar yields in contrasting MGs are achieved through different physiological processes. Our objectives were: (i) to characterize biomass accumulation, reproductive partitioning and seed set efficiency, and (ii) to analyze the role of N and radiation in biomass accumulation during the seed set period in contrasting MGs. Three MG III and V cultivars were tested in two growing environments. No significant yield or seed number differences were detected despite MG V had 20 d longer growth cycle. MG III had a longer seed set period (R1-R5), received more incident radiation during that period, and captured more N compared to the MG V. However, these cultivars had lower nitrogen use efficiency (NUE) (g biomass per g N uptake) and less radiation interception efficiency compared to MG V. These contrasting physiological processes determined similar biomass accumulation during R1 to R5. No differences between MGs were observed in biomass partitioning to reproductive structures and seed set efficiency during this period. Results showed contrasting MGs have different strategies for reaching similar yield, evidencing physiological processes that could be specifically tailored by breeders for either MG III (radiation interception efficiency, NUE) or MG V (duration of R1-R5 period, N uptake rate) cultivars for further yield increases.