Recommended databases for interdisciplinary topics are Research Library (ProQuest) and EBSCOhost. Both will bring up online journal articles, Ebooks and more. From the search results page, you can limit to recent publications, format (books, articles) and more.
Specific resources for each topic are listed below.
Search key words, not sentences. Try synonyms and broader terms like biofarming for aquaponics or hydroponics
In EBSCOhost and ProQuest, combine terms using the Advanced search: "animal feed" AND "drug resistance"
In Google combine them using plus and minus signs: "animal feed" +"drug resistance"
In Google, try limiting your search by adding site:.gov or site:.edu or site:.eu to your search string
Antibiotics use in agriculture is a topic in many disciplines: agriculture, medicine, politics. Try an interdisciplinary search in ProQuest or EBSCOhost.
Example searches: livestock AND antibiotics
swine AND antibiotics
"animal feed" AND "drug resistance"
GMO is a topic in many disciplines. Try an interdisciplinary search in Research Library (ProQuest) or EBSCOhost.
example searches: GMO or "genetically modified organism" AND food
Subject: Transgenic organisms
Try a Subject search: "organic agriculture"
Search the phrase "urban agriculture" in quotes in Ivy Cat or Discover