Nutrient Use Efficiencies in Soybean: A Review.

Cropping systems currently face dual challenges of maximizing yields in a sustainable approach. The importance of a balanced nutrition is critical for increasing crop production. In the past decades, comprehensive studies were performed for nitrogen (N) in corn and for phosphorus (P) in soybean. From a physiological standpoint, a synthesis-analysis on N, P, and potassium (K) content, utilization, interaction between nutrients and final impact on yield is relevant and needed for properly understanding scientific knowledge gaps on this nutrient. Historical and geographical (USA vs. World – excluding USA) grain yield and N, P, and K content was characterized for soybean. Historical USA soybean yield research trend mimicked a similar pattern as portrayed by the USDA (1920-2012) yield database. The historical yield trend depicted a parallel N, P, K uptake pattern [except for the last yrs (2012 season, drought stress)]. For soybean, high-yielding data points were closely related with balanced N/K ratio close to 2:1. For N, increasing nutrient utilization efficiency was tightly connected with lower grain N concentration; while for K was associated with lower K content in the stover (reduction in stover %K). Outlooks for concurrent yield and nutrient use improvements are great challenges that need to address ecological yield intensification, without overlooking the biofortification issue.