Lugo-López, M. A. and Abrams, R. (1981) “High Yields of Non-fertilized Protein-rich Pigeon Peas on Tropical Soils of Low Inherent Fertility of Puerto Rico: An Explanation of a Paradox”, The Journal of Agriculture of the University of Puerto Rico, 65(1), pp. 21–28. doi: 10.46429/jaupr.v65i1.7558.