Bonnet, J. A., A. R. Riera, and J. Roldán. 1958. “Yield Responses to Different N-P-K Levels, and Correlations With Foliar Analysis, in Sand-Culture Studies With Corn, Sugarcane, and Cotton”. The Journal of Agriculture of the University of Puerto Rico 42 (3):168-84. https://doi.org/10.46429/jaupr.v42i3.13608.