Potassium Accumulation and Partitioning in Three Soybean Genotypes Differing in Maturity Group.

Understanding the uptake and distribution of nutrients among plant structures and across time is required to develop diagnostic information to assess plant nutritional health. We evaluated season-long dynamics of K uptake and allocation to aboveground plant parts in representative determinate [maturity group (MG) 5.3] and indeterminate (MG 3.9 and 4.8) soybean [Glycine max (L.) Merr] varieties in 2012 and 2013. Whole-plant samples and recently matured trifoliolate leaves were collected 8-10 times between V5 and maturity and whole-plants were partitioned into leaves, petioles, stems and branches, pods, and seeds. Each parameter was statistically analyzed by year due to differences in planting date (22 May 2012 and 26 June 2013). Within each year, aboveground K uptake was similar among varieties ranging from 118 to 148 (2012) and 125 to 132 (2013) kg K ha^-1 but peak accumulation among varieties occurred at a different number of days after emergence (DAE). Potassium accumulation peaked for all varieties at R5.5-6.0 stage, which occurred 78 (2013) and 98 (2012) DAE for the MG 3.9 and 4.8 varieties and 94 (2013) and 111 (2012) DAE for the MG 5.3 variety. The predicted rate of maximum K accumulation occurred at R3-4 stage for all varieties ranging from 2.01 to 2.27 (2012) and 1.77 to 2.39 (2013) kg K ha^-1 d^-1. In 2012, the trifoliolate-leaf K concentration peaked at R2 stage (14.2-16.3 g K kg^-1) for all varieties and declined linearly at a rate of 0.16 g K kg^-1 d^-1 until leaf senescence (R7). In 2013, trifoliolate-leaf K concentration peaked at R1 stage (19.8-20.6 g K kg^-1) and declined linearly, but the decline rate differed among varieties (0.06-0.21 g K kg^-1 d^-1). At R7 stage, on average, seed comprised 40-51% of the aboveground dry matter (7,389-10,718 kg ha^-1) and 49-69% of the aboveground K content (114-138 kg K ha^-1).