O. W. Ritter, O. E. Jauregui, R. S. Guzman, B. A. Estrada, N. H. Muoz, S. J. Suarez and V. M. C. Corona, “Eco logical and Agricultural Productivity Indices and Their Dynamics in a Sub-Humid/Semi-Arid Region from Cen tral México,” Journal of Arid Environments, Vol. 59, No. 4, 2004, pp. 753-769. doi10.1016/j.jaridenv.2004.02.009 - References - Scientific Research Publishing