APA (7a ed.)

Bahrt, G., Brown, B., Camp, A., Chapman, H., Cooper, H., Davidson, O., De Turk, E., Hoffer, G., Jones, H., Mcmurtrey, G. N., Parker, E., Salter, R., Scarseth, G., & Skinner, J. J. (1941). Hunger signs in crops : a symposium. The American Society of Agronomy; The National Fertilizer Association.