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.
An integrated system of plant and animal production practices having a site-specific application that will, over the long-term— (A) satisfy human food and fiber needs; (B) enhance environmental quality and the natural resource base upon which the agriculture economy depends; (C) make the most efficient use of nonrenewable resources and on-farm resources and integrate, where appropriate, natural biological cycles and controls; (D) sustain the economic viability of farm operations; and (E) enhance the quality of life for farmers and society as a whole.