Changes in Phosphorus Uptake in Soybean Cultivars Released over 90 Years.

Plant breeding effort and improvement in agronomic technologies resulted soybean [Glycine max (L.) Merr.] yield gain in the last century. There are limited knowledge about how nutrient uptake, such as phosphorus (P), and their partitioning have changed through the growing season over time. Field studies were conducted to determine P partitioning patterns in soybean varieties released over the last nine decades. Twenty-five cultivars were selected from maturity group (MG) II starting from 1928, and 26 cultivars from MG III that were released starting from 1923. The cultivars were sampled throughout the growing season [V4 (four expanding trifoliates), R2 (full bloom), R4 (full pod), R6 (full seed), and R8 (physiological maturity)], and were partitioned to leaves, stems, pods, stover, and grain fractions if available. Phosphorus uptake was calculated for each plant fraction of each sampling time. Plant part's P contents were subject of regression analysis to determine the changes over time for the various plant fractions through the growing season. In MG II, changes in P content and uptake were best explained by quadratic regression model starting from R2 growth stage; showing increasing P uptake in cultivars released after about 1970. Cultivar’s P uptake linearly increased with more recent release year until the R4 growth stages; after that, quadratic regression model explained the best of P uptake changes over time in MG III. Grain P uptake at physiological maturity nearly doubled in the most recently released cultivar relative to the oldest cultivars for both MGs while grain nutrient concentrations decreased in newer cultivars.