1. National Agricultural Statistics Service 2007http://www.agcensus.usda.gov/Publications/2007/index.php
2. Agricultural Research Service. FY-2005 Annual Report Manure and Byproduct Utilization National Program 206http://www.ars.usda.gov/research/programs/programs.htm?np_code=206&docid=13337
3. National Organic Program Rule-Soil Fertility and Crop Nutrient Management Practice Standardhttp://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&SID=2e169858257b8657bc0c02 3591b8183c&n=7y3.1.1.9.32.3&r=SUBPART&ty=HTML
4. Economic Research Service. Organic Market Overviewhttp://www.ers.usda.gov/topics/natural-resources-environment/organic-agriculture/organic-market-overview.aspx#.UbnZfdhsOAI