Abruña, F., J. Vicente-Chandler, J. Figarella, and S. Silva. “Potassium Supplying Power of the Major Ultisols and Oxisols of Puerto Rico”. The Journal of Agriculture of the University of Puerto Rico, vol. 60, no. 1, Jan. 1976, pp. 45-60, doi:10.46429/jaupr.v60i1.10585.