The Collaborative International Dictionary of English v.0.48:

Agronomy \A*gron"o*my\, n. [Gr. ? rural; as a noun, an overseer
   of the public lands; ? field + ? usage, ? to deal out,
   manage: cf. F. agronomie.]
   The management of land; rural economy; agriculture.
   [1913 Webster]

WordNet (r) 3.0 (2006):

agronomy
    n 1: the application of soil and plant sciences to land
         management and crop production [syn: agronomy,
         scientific agriculture]