Soil contains iron, but not the right kind

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Question: Can I use filings from resurfacing auto brake shoes and rotors to add iron to my vegetables?

I wish it was that easy. Just adding iron to the soil is not enough to help your vegetables. Actually, there is quite a bit of iron in our soils already. Most of the red color we see in our desert soils and rocks is due to iron.

But the iron in our soils and rocks is the wrong kind for plants to use, just like the iron from brake shoes. The high pH or alkalinity of our desert soils prevents the iron contained in it from becoming available to plants. As soil alkalinity or pH increases, the iron already in the soil becomes less available.

Iron can exist in two different states -- a plant-available ferrous form and an unavailable ferric form. Iron can shift between these two states, depending upon the alkalinity of the soil and how much air is present. A good example of the ferric form of iron is rust, which is what you'll get when you add brake shoe filings to the soil. Because of the high pH of our soils, most of the iron is in the ferric state, the form unavailable to plants.

In theory, you should be able to release iron from our soils if you decrease the alkalinity or lower the soil pH. And this is true. One product sold locally called Ironite is based upon this principle. This doesn't always work because any lowering of the soil's alkalinity is only temporary. Sooner or later, the soil returns to its alkaline nature and the iron soon becomes unavailable again.

This is where iron chelates come into play. Chelates are chemicals that are able to prevent elements like iron from shifting from one form to another. Chelates also prevent elements, like iron, from binding to other chemicals in the soil, also making it unavailable.

Just using any old iron chelate is not going to guarantee that it will work in our soil. The best all-around chelate to use for applying iron to our soils has the acronym EDDHA in the list of ingredients.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension.