AGRISis an international collection of ag-related papers, data, reports, and more, from the Food and Agriculture Organization of the United Nations (FAO). Many item records include direct links to free full-text.
AgEcon Search provides full-text scholarly research in agriculture and applied economics, hosted at the University of Minnesota and including research from many institutions and agencies.
Based in Switzerland, MDPI publishes international, scientific, peer-reviewed, open access (free) journals . Some of their Ag-related titles include: Agriculture, AgriEngineering, Agronomy, Animals, Horticulture, Land, Soil Systems, Veterinary Sciences, and more.
Though the journals are not free, many journals published by Elsevier include a number of open access articles in each issue. The journal websites will note "open access" on the articles that are free.