There aren't databases specific to sustainable agriculture. For articles on these topics, use any agricultural database and just use keywords that differentiate if you need literature specifically on sustainable agriculture. Also, the NAL agricultural thesaurus could be of help for finding related terms to sustainable agriculture that can help in keyword searching/selection.
A few databases that I like for agriculture in general:
Our full list of databases on and related to agriculture: http://instr.iastate.libguides.com/az.php?a=all&s=13811
NAL Agricultural Thesaurus: https://agclass.nal.usda.gov/
Below is the entry in the thesaurus for Sustainable Agriculture.