While iron is the fourth most common element in the Earth’s crust and most soils contain abundant levels of it, many times naturally occurring iron is not found in the forms most readily available for plant uptake

Iron was first discovered as necessary for plant health in the 1800s, when iron-deficient grapes were successfully treated with foliar applications of iron-bearing salts. Later research showed plants themselves are equipped to chemically alter some naturally occurring iron with root exudates to facilitate uptake. Still, modern agronomic studies and practices point to soil pH as a primary factor to consider in how well root biology can supply crops with iron in the soil.

Iron & pH

Since research shows most grain crops remove less than 2 pounds of iron per acre in a season, most soils with a pH of 7.0 or less are generally capable of meeting crop iron needs. In areas where evapotranspiration exceeds precipitation, however, downward water movement is insufficient to leach solutes out of the soil profile and salts can precipitate. 

Throughout the rest of the country, there are other factors affecting topsoil’s ability to provide iron for plant growth, such as soil compaction and drainage issues that might restrict root zone conditions and soil samples that indicate high pH values or concentrations of calcium carbonates.

While iron deficiencies can affect most crops, soybeans seem to be particularly sensitive to the shortages, which has created a significant body of information on the need for iron in the diet of…