In several of its aspects the problem of the availability of iron for plants is still unsolved. If the problem is not unique, it is at least unusual. In general, the plant takes its elements in simple combinations - almost, the simpler the better. Phosphorus is picked up as phosphate, nitrogen as nitrate or ammonia, sulphur as sulphate, and metals can be given as salts - nitrates, sulphates and chlorides. But try putting ferric chloride into a nutrient solution with a reaction around the neutral point! The plant turns yellow; the leaves become chlorotic, and there are all the indications of iron deficiency.
Proceedings of the Iowa Academy of Science
©1936 Iowa Academy of Science, Inc.
Clark, Norman Ashwell
"Green Plants and the Reactions of Iron,"
Proceedings of the Iowa Academy of Science, 43(1), 185-189.
Available at: https://scholarworks.uni.edu/pias/vol43/iss1/39