1. World Agricultural Production: Monthly Circular Series for World Agricultural Production,2012
2. http://www.nass.usda.gov/Statistics_by_Subject/index.php?sector=CROPS
3. http://www.fao.org/worldfoodsituation/wfs-home/foodpricesindex/en/
4. Global Climate Projections;Meehl,2007
5. Cover Crops for Sustainable Agrosystems in the Americas;Scholberg,2010