Iron

Iron (Fe) is an essential nutrient for plant growth, but because only a small amount is needed, it is classified as a micronutrient.  Iron is also essential for many plant functions. To note a few:

•  Iron draws energy to the leaf by absorbing heat from the sun; it makes the leaf darker, thus absorbing more energy. It will increase the waxy sheen of the crop. 
• Iron iis necessary for the maintenance and synthesis of chlorophyll and RNA metabolism in the chloroplasts. 
• Iron increases the thickness of the leaf, [which] increases nutrient flow geometrically, resulting in a production increase geometrically
• Iron is needed by nitrogen fixing bacteria
• Both iron and manganese become less available at pH 7 and above and in the absence of organic matter and water.
• When iron deficiency is serious, the entire leaf will turn yellow, leaving only the veins to stand out like road maps
• Iron will increase the waxy sheen of the cropalso affects the flavor, the storageability, and the sugar content of fruits, Buds, etc..
• Iron is very important to the formation of lignin in plant cell walls which contributes to the structural strength of the cells, and the plant.