Delgado, J. A., Gross, C. M., Lal, H., Cover, H., Gagliardi, P., McKinney, S. P., Hesketh, E., and Shaffer, M. J., 2009, Chapter 4 - A New GIS Nitrogen Trading Tool Concept for Conservation and Reduction of Reactive Nitrogen Losses to the Environment: Academic Press, v. Volume 105, p. 117-171.