Soybean Uptake, Partitioning, and Removal of Various Nutrients Across a Wide Yield Range.

Precise knowledge of soybean nutrient requirements and utilization is imperative as growers look to more efficiently achieve greater soybean [Glycine max (L.) Merr.] yields.  Unfortunately, soybean  nutrient uptake and partitioning models are primarily built from work conducted in the early 1960’s with obsolete soybean genetics and production practices.  Since the 1960’s, yields have nearly doubled to 3,150 kg ha^-1 in 2015 and soybean physiology has been altered with approximately one more week of reproductive growth and greater harvest index’s for currently cultivated varieties.  These changes in soybean development along with new production practices warrant re-evaluating soybean nutrient uptake, partitioning, and removal to help guide soybean fertility recommendations.  This study’s objective was to re-evaluate these factors across a wide yield range of 2,685 – 6,700 kg ha^-1.  Trials were conducted at three locations (Arlington and Hancock, WI and St. Paul, MN) during 2014 and 2015. Plant samples were taken at the V4, R1, R4, R5.5, R6.5, and R8 growth stage and partitioned into stems, petioles, leaves, pods, seeds, fallen leaves, and fallen petioles, totaling more than 3,300 samples annually.  Results indicate that dry matter accumulation at R6.5 was only 86% of the total and that as yield increased the harvest index also increased, but was environment specific.  Nutrient uptake for N, P₂O₅, and K₂O pooled across all environments was 279, 66, and 188 kg ha^-1, respectively and crop removal was 232, 55, and 90 kg ha^-1, respectively at a yield level of 4,421 kg ha^-1.  Crop removal was not affected by the environment, while total nutrient uptake was. This data showed that the extended reproductive growth phase, greater nutrient remobilization efficiencies (>70%), and a higher harvest index with increasing yields helped contribute to higher yields without greatly increasing total nutrient uptake.