Shifts in Soybean Yield, Nutrient Uptake, and Stoichiometry: A Historical Synthesis-Analysis.

Over the last decades, the study of nutrient uptake and partitioning in soybean has been increasingly acknowledged in the scientific literature. Nonetheless, scarce studies investigated the improvement of nutrient use efficiency within a plant perspective, by dissecting yield-to-nutrient uptake ratio (internal efficiency, IE) and by evaluating changes in nutrient stoichiometry over time. Following this rationale, a comprehensive synthesis-analysis was performed to discern trends in IE and nutrient stoichiometry for soybeans as related to yield and other plant traits of importance for our crop ecology and breeding community. The historical analysis was tested by dissecting the database (1921-2016) in three Eras providing the main findings of this synthesis-analysis: i) a 32% increase in soybean yields from Era II to Era III was primarily driven by changes in plant biomass rather than by modifications in HI; ii) the N and P HIs increased over time; while K partitioning to seed (KHI) decreased. Seed nutrient concentration in soybeans remained stable for N, but a large reduction was documented for P (-18%) and K (-13%). Stover nutrient concentration decreased comparing Era I and III for N, P and K, iii) nutrient IE for N and P showed large increase (33% and 44%, respectively) among years; while for K, there was a significant decrease (15%); iv) variations in yield-to-nutrient uptake ratio were primarily explained for nutrient HI in the case of N and K, and equally explained by both PHI and P_seed for P; and v) the N:P and N:K nutrient ratios were reduced over time, while the K:P ratio increased for the last two Eras. This improved knowledge of the main physiological factors underpinning the nutrient IE and stoichiometry over time could guide soybean programs focused on achieving superior nutrient utilization in concomitance with sustaining and closing yield gaps.