Final answer:
Agriculturalists differ from horticulturalists primarily in the use of machinery and scale; agriculture is large-scale and mechanized, while horticulture is small-scale and uses simple tools.
Step-by-step explanation:
The key factor that distinguishes agriculturalists from horticulturalists is the use of machinery. Horticulture refers to small-scale plant cultivation carried out with simple tools and hand labor, employing methods like slash-and-burn and the planting of multiple crops in small plots. In contrast, agriculture involves intensive methods such as the use of plows, draft animals, irrigation systems, and the continuous cultivation of the same plots. Agriculturalists manage large-scale farms, often focusing on a single crop (monoculture), and heavily rely on mechanization, as well as technological innovations, to enhance productivity.