Physiological and management factors contributing to soybean potential yield

• Soybean yield potential is characterized by physiological traits and environmental factors impacting seed number and average mass per seed.
• Potential yield estimates from research, yield contests, and crop simulations range from 7000 to 11,000 kg ha−1.
• Future prospects for increasing potential yield through management and genetic improvement are discussed.

The largest reported soybean grain yield is approximately three-fold more than the highest reported U.S. average yield. An understanding of yield determination is needed to identify avenues for increasing yield and for defining the yield potential of soybean. To illustrate physiological traits important for yield determination, we used a framework that models yield as the product of seed number (seed m−2) and individual seed mass (massseed). Developmentally, seed m−2 is determined first and is proportional to the biomass accumulation rate (BAR, g m−2 d−1) and the fraction of assimilate allocated to reproductive structures. Seed m−2 is inversely proportional to the individual seed growth rate (ISGR, mg seed−1 d−1) where the ISGR represents the minimum amount of assimilate necessary to prevent a flower or pod from aborting. Hence, seed m−2 can be increased by optimizing conditions for crop growth (e.g., radiation interception, stress-free environment, high soil fertility levels) and having a low ISGR. Determination of massseed occurs later during ontogeny than seed m−2 and can be expressed as the product of the ISGR and the effective seedfilling period (EFP, d). Variation among genotypes for ISGR is quite large and is generally not affected greatly by the environment. There is also genotypic variation in the EFP, but the EFP is decreased by a variety of biotic and abiotic stresses. Our analysis indicates that reaching the potential yield of soybean depends upon high BAR and extending the EFP, and a key factor affecting both of these variables is ensuring non-limiting crop nutrition, especially nitrogen. Strategies for increasing soybean maximum yield include early planting (which extends the EFP), optimizing crop nutrition, minimizing biotic and abiotic stresses, and developing breeding programs tailored for high yield environments. Characterizing physiological traits important for yield with genetic markers offers tools for combining favorable traits for high-yield environments.