A. R. Vasquez and A. M. L. Neptune, “ Foliar fertilization of young coffee plants (Coffea arabica, L.) with three sources of nitrogen - 15N ”, An. Esc. Super. Agr. Luiz de Queiroz, vol. 34, pp. 565–584, Jan. 1977, doi: 10.1590/S0071-12761977000100044.