References
- California Department of Food and Agriculture . December 1990 . “ California code of regulations, title 3, sections 2300 through 2326 ” . December , 25 Sacramento , CA 95814
- Charter , R.A. , Tabatabai , M.A. and Schafer , J.W. 1993 . Metal contents of fertilizers marketed in Iowa . Commun. Soil Sci. Plant Anal. , 24 : 961 – 972 .
- 1985 . Western Fertilizer Handbook , 7th ed. , Danville , IL : Soil improvement committee of the California fertilizer association . Interstate Printers and Publishers, Inc.