Impact Metrics for Crop Nutrition Sustainability in North America.
Thomas W. Bruulsema, International Plant Nutrition Institute, Guelph, ON, Canada, Paul E. Fixen, International Plant Nutrition Institute Americas and Oceania Group, Brookings, SD, Robert M. Norton, International Plant Nutrition Institute, Oceania, Horsham, Victoria, Australia and Clifford S. Snyder, International Plant Nutrition Institute Americas Group, Conway, AR