• Test Environments: 2 years at 3 locations with non-limiting fertility levels, resulting in 6 different testing environments.
• Soybean Varieties: 8 Pioneer® brand soybean varieties (RM 1.0-2.5)
• Planting Dates: Early and late May
• Plant Sampling: Collected at the V4, R1, R4, R5.5, R6.5, and R8 growth stages and partitioned into the following parts:

-Stems                 -Petioles

-Leaves                -Pods

-Seeds                  -Fallen Leaves/Petioles

• Nutrients Quantified: Phosphorus and potassium, presented in fertilizer equivalents (P2O5 and K2O)
• 6,672 tissue samples analyzed that span a yield range of 40 to >100 bu/acre.

• Across all environments and varieties, the soybean plant took up an average of 0.9 lbs of P2O5/bu/acre. Potassium uptake was more than double this at 2.3 lbs of K2O/bu/acre. Therefore, an 80 bu/acre soybean crop accumulated 73 and 200 lbs of P2O5 and K2O, respectively, by R8 (Figure 1).
• More variability existed in the relationships between P2O5 and K2O uptake and yield than the relationship between N uptake and yield (R2 = 0.80). This was due to the fact that both P2O5 and K2O uptake were greatly affected by the environment, with K2O experiencing the greatest variability in uptake associated with environmental differences and therefore lowest R2 value.
• As displayed in Figure 3, 90% of total K2O uptake is accumulated by R5 (beginning seed fill) but seeds/m2 and seed size are far from being determined. This lack of overlap and the fact that soybean is a luxury K2O consumer certainly contribute to the moderate relationship between total K2O uptake and seed yield (R2 = 0.53) (Figure 1).

• The potassium uptake rate accelerated quickly after V2 to a peak rate of 4 lbs K2O/acre/day at R2 and then sharply decelerated through R6 (Figure 2).
• Phosphorus displayed a more gradual build and decline before and after the peak uptake rate (1 lb P2O5/acre/day), which occurred at R3 (Figure 2).

• Relative uptake prior to R1 was minimal for P2O5 (13%), but greater than 25% for K2O. Leaves and stems were large storage organs for P2O5, while K2O was more equally distributed to all plant parts.
• Seed K accumulation relied more heavily on vegetative remobilization compared to P2O5 (76 vs. 52%), yet the nutrient harvest index (HI) was much higher for P2O5 (81%) than K2O (49%) and was similar to the N HI (83%) at the same yield level (Figure 3).
• The large K2O uptake requirement (2.3 lbs K2O/bu/acre) and low K2O HI makes stover removal a major pathway for K2O removal and soil K2O depletion if not replaced with fertilizer.

• Total P2O5 (0.74 lbs./bu/acre) and K2O (1.17 lbs/bu/acre) removal with the grain was consistent across all varieties and environments. Therefore, an 80 bu/acre soybean crop removed 59 and 98 lbs of P2O5 and K2O, respectively (Figure 4).
• In comparison a 200 bu/acre corn crop would remove similar amounts of P2O5, but only half the amount of K2O.