Del Valle, Jr., R., Scott, T.W. and Lugo-López, M.A. 1979. Response of Irish Potatoes to Various Levels of N and Time of N Application in an Ultisol. The Journal of Agriculture of the University of Puerto Rico. 63, 3 (Jul. 1979), 344–350. DOI:https://doi.org/10.46429/jaupr.v63i3.10293.