You can find scholarly research by searching a large multidisciplinary databases or by a searching smaller, agricultural database.

There are advantages to each database. If I'm really trying to be thorough, I will utilize several databases. There will be significant overlap in coverage within those databases.

Best Databases for Finding Agricultural Science Research

The largest database is the Washington State University Library Catalog (Search It). Search It locates pretty much everything you'd hope to find on a subject. This includes journal articles, books, newspapers, multimedia, extension resources, archival materials, etc. It searches across a large number of databases including the ones listed below. 

A smaller, but still extremely powerful database, is  Web of Science. Web of Science is a mostly STEM database. Aside from being a scholarly database it also includes many useful features including citation reports and impact analytics.

If you want to go even more disciplinarily specific, try AGRICOLA which is an agricultural sciences scholarly database. AGRICOLA is maintained by the U.S. Department of Agriculture's National Agricultural Library. 

If you are interested in what databases are available to you at WSU, check out this list.