Methods of Soil Analysis — Chemical Methods, D.L. Sparks, A.L. Page, P.A. Helmke, R.H. Loeppert, P.N. Soltanpura, M.A. Tabatai, C.T. Johnston, M.E. Summer (Eds.). Soil Science Society of America, Inc., American Society of Agronomy, Inc., Dordrecht/Boston/London (1996), 1,358