In which agricultural situation are fertilizers least necessary?

In a natural prairie pasture where cattle feed and defecate, fertilizers are least necessary because the ecosystem is already well-suited for nutrient cycling. This type of environment typically has a diverse range of native grasses and plants that are adapted to the local soil and climate conditions. The presence of cattle contributes organic matter to the soil through their feed residues and manure, which replenishes nutrients naturally.

In this scenario, the natural processes of decomposition and nutrient cycling help maintain soil fertility without the need for additional synthetic fertilizers. In contrast, the other options describe agricultural systems that rely on external inputs for nutrient management. For instance, a pumpkin patch harvested only in the fall still requires nutrient replenishment for the next growing season, and a cornfield grown for export requires significant fertilization to maintain high yields. Therefore, the natural prairie represents an ecosystem where fertilizers are least needed due to its self-sustaining nutrient dynamics.