del Valle, Jr., Reinaldo, Richard H. Fox, and M. A. Lugo-López. “Response of Soybeans Grown in an Ultisol to Residual Broadcast and Banded P Fertilizer”. The Journal of Agriculture of the University of Puerto Rico 61, no. 2 (April 1, 1977): 179–186. Accessed May 26, 2022. https://revistas.upr.edu/index.php/jaupr/article/view/10456.