Question

Read the passage below:

While nineteenth-century agricultural chemistry was long dominated by Justus von Liebig's "mineral theory"—which asserted that plants absorb nitrogen exclusively from inorganic soil nitrates derived from decaying organic matter—the French agronomist Jean-Baptiste Boussingault introduced a methodological counterweight through precise quantitative crop-rotation accounting. Boussingault measured the total nitrogen content of seeds, harvested crops, and soil amendments across multi-year rotations on his Alsatian estate. Crucially, he observed that leguminous plants such as clover accumulated significantly more nitrogen than could be accounted for by soil depletion alone, whereas cereal crops exhibited a strict nitrogen deficit relative to soil inputs. Although Boussingault stopped short of identifying the biological mechanism—namely, symbiotic bacterial nitrogen fixation in root nodules, which was not demonstrated until decades later—his empirical accounting directly challenged Liebig's reductionist chemical framework. By demonstrating that certain crop sequences actively enriched soil nitrogen reserves, Boussingault provided a rigorously documented rationale for traditional crop rotation practices that mainstream chemical theory had previously dismissed as mere empirical folklore.

Which of the following best describes the primary rhetorical function of the sentence noting that leguminous plants accumulated significantly more nitrogen than could be accounted for by soil depletion alone?