Rhododendron shows signs of severe yellowing leaves due to iron deficiency. The most effective way to apply iron is in what form?

• A. Chelate
• B. Nitrate
• C. Sulfate
• D. Oxide

Answer: (A)

Iron deficiency in rhododendrons shows up as yellowing leaves because iron becomes unavailable when the soil is not acidic enough. The most effective way to supply iron is in a chelated form because the chelate binds iron and keeps it soluble in the soil solution, even as pH can rise. This prevents iron from precipitating as insoluble compounds like hydroxides or oxides and makes it readily absorbed by the roots (and can also be taken up by leaves if used as a spray). Other forms, such as oxide, sulfate, or nitrate, tend to be less reliable because they can become insoluble or cause unwanted pH changes, reducing the amount that actually reaches the plant. Chelated iron stays available across a wider pH range and thus corrects the chlorosis more effectively in rhododendrons.