Nitrogen and Phosphorus Uptake in Determinate and Indeterminate Soybean of Different Maturity Groups.

Soybean [Glycine max (L.) Merr] nutrient uptake across time is important to understand the nutrient requirements for high yields. Our objective was to evaluate aboveground N and P uptake patterns in representative determinate [maturity group (MG) 5.3 or 5.5] and indeterminate (MG 3.9 and 4.8) soybean. We collected 15 whole-plants and recently matured trifoliolate leaves 8-10 times from V5 to maturity in 2012 and 2013. Data were statistically analyzed by year. Within each year, the maximum aboveground N uptake among cultivars was similar ranging from 329 to 371 kg N ha^-1 in 2012 and 273 to 311 kg N ha^-1 in 2013. Nitrogen uptake peaked at the R6.5-7.0 stage, 92-95 (2013) and 107-111 (2012) days after emergence (DAE) for the indeterminate cultivars and 106 (2013) and 125 (2012) DAE for the determinate cultivar. The predicted maximum N uptake rate occurred at the R5 stage ranging from 5.06 to 5.72 kg N ha^-1 d^-1 in 2012 and 4.42 to 5.46 kg N ha^-1 d^-1 in 2013. The maximum aboveground P uptake among cultivars was different amounting to 26, 29, and 32 kg P ha^-1 in 2012 and 23, 20, and 21 kg P ha^-1 in 2013 for the MG 3.9, 4.7, and 5.3/5.5 cultivars, respectively. Phosphorus uptake peaked at the R6-7 stage, 103-124 DAE in 2012 and 90-120 DAE in 2013. The predicted maximum P uptake rate occurred at the R4-5 stage ranging from 0.45-0.47 kg P ha^-1 d^-1 in 2012 and 0.25-0.38 kg P ha^-1 d^-1 in 2013. Each year, trifoliolate-leaf P concentration for all cultivars peaked at R1-2 stage [3.0-3.5 (2012) and 3.3-3.7 (2013) g P kg^-1] and declined non-linearly until the R7 stage. Regardless of soybean maturity group, maximum N and P uptake rates peak at the R4-5 stage and maximum aboveground uptake peaks at the R6-7 stage.