Reference works are an excellent first stop in your research and are incredibly useful for:
Encyclopedias and dictionaries, while useful, are not usually cited in your research. Ask your librarian or instructor about citing a reference work to be sure.
(Conventional irrigation sprinkler system on a field, Lance Cheung. CC Public Domain Mark 1.0 Universal https://creativecommons.org/publicdomain/mark/1.0/.)