Engelstad, O. P., Boswell, F. C., Welch, L. F., Tucker, T. C., Dinauer, R. C., Ernst, S., & Mortvedt, J. J. (1985). Fertilizer technology and use (Third Edition.). Wisconsin, Estados Unidos: Soil Science Society of America, Inc..

Engelstad, O. P.,, F. C. Boswell, L. F. Welch, T. C. Tucker, Richard C. Dinauer, Susan Ernst, and John J. Mortvedt. Fertilizer Technology and Use. Third Edition. Wisconsin, Estados Unidos: Soil Science Society of America, Inc., 1985.

Engelstad, O. P.,, et al. Fertilizer Technology and Use. Third Edition. Wisconsin, Estados Unidos: Soil Science Society of America, Inc., 1985.