6Kelner, D. J.; Vessey, J. K. and Entz, M. H.: The Nitrogen Dynamics of I-, 2-and 3-year Stands of Alfalfa in a Cropping System, Agriculture, Ecosystems & Environment, 64(1): 1-10, 1997.
7Sheaffer, C. C., Sollenberger, L. E.; Hall, M. H.; West, C. P. and Hannaway, D. B.: Grazing, lands, Forages and Livestock in Humid Regions, in Wedin, W. E and Fales, S. L. (eds.): Grassland." Quietness and Strength for a New American Agriculture, Madison, Wisconsin, USA: American Society of Agronomy, Crop Science Society of America and Soil Science Society of America, 2009.
