Clark, Andy (ed.), "Medics"(PDF), Managing Cover Crops Profitably (3rd ed.), Beltsville, Maryland: Sustainable Agriculture Network, archived from the original(PDF) on 2016-03-05, retrieved 14 June 2015
Clark, Andy (ed.), "Medics"(PDF), Managing Cover Crops Profitably (3rd ed.), Beltsville, Maryland: Sustainable Agriculture Network, archived from the original(PDF) on 2016-03-05, retrieved 14 June 2015