An agronomist specializes in which field?

Quite basically, soil scientists, not agronomists, specialize in soil. "Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils."

Wrong answer - soil scientists specialize in soil. Agronomists specialize in crops.