ScienceDirectory.info is a leading science website including agriculture, metrology, industrial engineering, earth sciences, geography, mathematic, aquaculture, aerospace and more.
ArabScientist.org.
Publishes a set of papers on agricultural topics, especially on topics relevant to the Arab countries.
http://www.arabscientist.org/
C&P Press Greenbook.net.
Reference information about agricultural chemicals used in crop production.
http://www.greenbook.net/
CAB Direct.
An easily searchable archive of summaries of the world's agricultural and applied life sciences literature, available at cost.
http://www.cabdirect.org/