AbstractSignificant differences in hydrogen ion (H+) efflux from soybean roots among soybean cultivars were found ranging from 0.5 to 2.4 pH units in 24 h. The hydrogen ion efflux was positively correlated with the cultivar's seed yield in three different soil series. On highly leached, low cation exchange capacity (CEC) Oxisol (less than 10 cmol/kg), the cultivars with high H+ efflux capacity yielded highest and accumulated the highest amount of nutrients at flowering. All macronutrients, except for Ca and Mg, decreased at the beginning of the seed stage. Hydrogen ion efflux was positively correlated to leaf K and the K/(Ca + Mg) ratio. The K/(Ca + Mg) ratio was positively correlated to biomass and yields, thus suggesting nutrient accumulation up to seed production. Results from the medium CEC Ultisol (10 to 20 cmol/kg) were similar to those from the low CEC soil. On the high CEC Vertisol (above 35 cmol/kg), the cultivars with high H+ efflux depleted the rhizosphere soil zone for K faster than those with low H+ efflux, giving positive correlations for seed and biomass yields but negative correlations with leaf K and the K/ (Ca + Mg) ratio.
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