IRON IN RELATION TO THE STIMULATION OF GROWTH BY HUMIC ACID

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Abstract
A large number of lines of evidence show that humic acid derived either from soil by extraction or from carbon compounds synthetically is a nutrient which may provide iron for the growth and nutrition of higher and lower plants in a form in general more highly available than that usually supplied by inorganic and organic compounds of iron such as the sulfate, chloride, tartrate, or citrate. Methods of preparation of humic acid are described and also the approximate concentration to be employed. Iron in iron humate is completely soluble and indefinitely stable above pH 4.5, and its use is especially recommended for growing higher green plants in neutral or alkaline solutions.