Agricola is a database of agricultural literature created by the National Agricultural Library of the USDA. It indexes journals, magazines, conference reports, theses and dissertations, books and book chapters from 1970 forward, though in some cases newer materials aren't there yet.
PubAg is a newer database created by the National Agricultural Library. Its focus is on more recent materials (1995- ) and peer-reviewed articles in particular. It is intended to be for agriculture what PubMed is for medicine-- a freely available database of the literature of the subject. PubAg augments but doesn't replace or supersede Agricola.
Looking for more information or international scope? Try CAB Abstracts,which is produced by the Centre for Agriculture and Bioscience International or CABI (was the Commonwealth Agricultural Bureaux). Still not getting what you want? Try Web of Science or Scifinder, linked below.
Search the Libraries' Catalog for books, dvds, and more. Some of the items that show up in Agricola are government documents; when we have these, they are often listed in the catalog.