11/6/2012 - By Matthew Shultz

Of all the minor or micronutrients, Iron is the most noteworthy. Despite not being needed in large amounts in plants, it is a critical nutrient in plant nutrition. Typically, plants only need 1-2 lbs. of elemental iron per acre per year, compared to the needs of Nitrogen at 80-200 lbs. per acre or more. Without iron, deficiency will develop.

Iron is a very common element on our planet, and is often in the form of iron oxide, which is virtually unavailable to plants.  In fertilizers it typically is in the form of a sulfate or chelate. Typically a good iron percentage to have in the bag is 1%, and sometimes higher. As so little is put in the bag, it is critical to mix well. If it settles, many plants will not get their iron supplement. Homogenous fertilizers such as our NPK Plus assure even distribution in the bag.

Iron availability is very pH sensitive. High pH soils above 7.0 tend to lock up iron. So plants considered acid loving are really iron loving. Growing them in high pH soils is difficult. Chelating molecules attach to various nutrients, including iron and help them across the root membrane. FeEDTA, works well in soils in a 6.0 pH or under. Fe DTPA works well in soils up to 7.0 pH. And the more expensive chelate FeEDDHA actually works pretty well in calcareous soils with pH levels up to 10.0.

Good root health is imperative for proper iron absorption. Only a small portion of the root actually absorbs iron. This zone is roughly 1-3 cm. from root tip and is known as the area of cell elongation and maturation. Anaerobic soils, where roots do not properly respire or breathe, will induce iron chlorosis. The iron may be there, but can not be pulled up. Healthy roots can release protons that will acidfy the soil directly surrounding the roots, helping iron availability.

Typically, iron levels are deficient if under 30 ppm in the leaf. As iron is immobile in plants,meaning new leaves will not steal it from old leaves, iron sprays are often helpful. A chelate is best. A powdered chelate often goes out at the rate of 8-12 ounces per 100 gallons water while a liquid chelate, often at 1 Qt. per 100. A ratio of not more than 2:1 is desired when comparing foliar iron levels with foliar manganese. If it gets lopsided either way, it can attribute to the deficiency of the lesser nutrient. All of that about iron. It must be important!