Successful gardeners know the myriad benefits of a carefully designed fertilization program. Fertilizers can foster healthy plant growth, increase disease resistance in plants, stave off insect infestations and offer many other important benefits. There are numerous types of materials used as fertilizers, each with a distinct set of effects on soil fertility. Therefore, knowing the effects on soil of one particular fertilizer substance is key to knowing if it is the right choice for your soil or not.
Ironite is a material commercially sold as a fertilizer. It is made from waste products from the Iron King large-scale mine located in Arizona and other large-scale mining operations. Controversy has surrounded Ironite for many years because it contains arsenic, lead and other heavy metals. Though producers claim that the heavy metals are in a form that do not pose a threat to human health or the environment at large, concerns over the leaching of heavy metals from Ironite use has led to a ban on Ironite fertilizer in Canada and prolonged research by the Environmental Protection Agency (EPA).
Ironite is marketed as a soil amendment for alkaline soils. Alkaline soils -- those with a pH reading from 7 to 14 -- often present growing problems for plants since the soil's alkalinity can interfere with a plant's ability to absorb iron from the soil. Phosphorus, a key plant nutrient, is also "fixed" in alkaline soils in a form that plants cannot use. Ironite is thus used to adjust the soil's pH to make it less alkaline and to allow the plant to more easily absorb iron and phosphorus.
A study conducted by the University of Arizona examined the effects of Ironite fertilizer when applied to a crop of oat plants. Indeed, the oat crops treated with Ironite had higher yields, possibly due to the use of the Ironite fertilizer. The study also attempted to establish the degree to which arsenic and lead are absorbed by the plants. While the levels of arsenic and lead in oats were noticeably higher in the early stages of testing, concentrations diminished to statistically insignificant levels by the time the oats were harvested.
The central cause of concern over the use of Ironite fertilizer on plants is not so much the plant's uptake or arsenic and lead as it is the probability of fertilizer runoff containing arsenic and lead to leach into water systems. The EPA has disputed claims by Ironite manufacturers that arsenic and lead in Ironite exist in forms that are not hazardous to humans and the environment, citing research that demonstrates that heavy metals in Ironite actually are in a form that is soluble in humans and animals.
- University of Arizona Cooperative Extension; Influence of Ironite and Phosphorus on Yield...; P.J. Eberhardt & L.J. Clark
- East Tennessee State University; Arsenic and Lead Leaching From the Waste Derived Fertilizer Ironite; Brajesh Dubey & Timothy Townsend
- Washington Toxics Coalition; Ironite Fertilizer: Arsenic and Old Waste