Leguminous cover crops could fix enough nitrogen to replace the amount of synthetic fertilizer used
"On a global scale, leguminous cover crops could fix enough nitrogen to replace the amount of synthetic fertilizer currently in use: see C. Badgley et al., “Organic agriculture and the global food supply,” Renewable Agriculture and Food Systems, 22, 2007 pp. 86-108."
Oliver De Schutter, “Report submitted by the Special Rapporteur on the right to food”, Human Rights Council, A/HRC/16/49: 11 [verified 4/15/14]