12 AGRONOMY NEWS

Managing Iron Chlorosis In Corn


Ferrous sulfate in the seedrow increased yield of susceptible and tolerant hybrids.

Some soils of the western plains and inter-mountain west have chemical and physical characteristics that cause iron deficiency in corn. Affected corn plants typically are stunted and have yellow (chlorotic) leaves with veins that remain somewhat green, resulting in a striped appearance. The severity of the symptoms varies from year to year depending on the weather; symptoms usually are worse in cool and wet conditions. Mild yellowing may disappear when the weather turns warmer and drier, but moderate to severe yield reductions are usually the result when chlorosis persists for the entire growing season.

We don't know exactly why certain soils cause iron chlorosis to develop, while other soils with similar characteristics produce healthy corn. Soil tests for iron (DTPA or AB-DTPA) do not always show low Fe levels, which complicates prediction of the problem. Affected soils do typically have high pH (7.8 or higher) and contain free lime (calcium carbonate). High sodium, poor drainage, low organic matter and high phosphorus have also been implicated. In some cases the problem lies in the subsoil (16-24 inches deep) rather than in the plow layer. Whatever the cause, iron availability (not necessarily iron levels per se) in these soils is very low. As a result, it is usually ineffective to try to correct the problem by broadcasting iron fertilizers. Applying soil amendments to modify soil pH is usually not an economical option, either.

The most commonly recommended approach is the use of chlorosis-tolerant corn hybrids. Genetic tolerance levels vary greatly from hybrid to hybrid, and most seed companies can provide information on each hybrid's level of resistance. In many cases, use of tolerant hybrids will provide an acceptable level of correction, but yield-limiting chlorosis will still develop in the most severe soils. In these cases, either foliar or seed-row applications of iron may be beneficial.

A commonly recommended approach for foliar application is to apply a 1% solution of ferrous sulfate heptahydrate (FeSO4•7H2O) every 7 to 10 days beginning when chlorosis first becomes evident and ending when emerging leaves are no longer chlorotic. Iron chelates are also water soluble and produce similar results to the ferrous sulfate without the risk of burning the leaves, but chelates are considerably more expensive than ferrous sulfate. When these guidelines are followed, foliar applications are usually effective, but economical yield increases may not occur if applications are made too late or if they are not repeated at the recommended intervals.

Table 2. Results from Nebraska small plot study showing effects of seed-row applied iron fertilizer on corn yield (average of 3 years).

A, B, C Treatments with a common letter are not significantly different within hybrid type (p<0.05).

Recent research at the University of Nebraska West Central Research and Extension Center was conducted to evaluate a second option for applying iron. In this study, iron fertilizer placed in the seed row consistently increased corn yield compared to an untreated check. Banding the fertilizer protects it from being tied up by the soil, and the seed-row placement enables the small roots of the corn seedling to access the iron early in the growing season. Dry ferrous sulfate applied at a rate of 50 to 100 pounds per acre (at a cost of $8.50 to $17.00 per acre) was the most effective treatment evaluated, but chelated iron (FeEDDHA at 2.5 to 4 pounds per acre) and a lower solubility iron sesquioxide (from Agrium U.S. Inc. applied at a rate of 200 pounds per acre) also produced smaller, but significant yield increases. Seed-row applied iron fertilizer produced substantial yield increases with both chlorosis-susceptible and chlorosis-tolerant corn hybrids (Table 1). The yield benefit varied from year to year as the weather influenced chlorosis severity, but a positive response was observed in every year.

Some producers and agronomists may be hesitant to place fertilizer materials in direct contact with the seed at these relatively high application rates because of the risk of salt damage to emerging seedlings. This concern appears to be unwarranted as the Nebraska results showed no evidence of stand reduction, except in 2 of 5 years when ferrous sulfate was applied at a rate of 150 pounds per acre. No stand reduction was observed at application rates of 100 pounds per acre or less.

While the dry iron materials are very effective, many producers feel they are less convenient than liquids. Chelated iron can be dissolved in water and applied as a liquid, but this is probably not economical due to the high cost of chelates. A liquid formulation of ferrous sulfate is not currently available commercially, and because the solubility of ferrous sulfate limits the concentration of a liquid formulation to 5% iron, a suitable commercial product may not be forthcoming. A 5% iron solution, made by dissolving ferrous sulfate in water, was evaluated in the Nebraska research. While it was effective in both small and large plot trials, its performance did not equal that of the dry ferrous sulfate, probably because the low solubility limited the total amount of iron that could be applied per acre.

Chlorosis development is usually spotty and, while the severity of chlorosis varies from year to year, the location of these areas within a field usually remains consistent. Thus, the most economical approach to managing iron deficiency chlorosis in these fields may be to apply fertilizer materials only to those areas in the field where chlorosis is a consistent problem. Research is now being conducted to evaluate this site-specific approach on a production scale.

Bart Stevens
Extension Soils Specialist
Powell Research and Extension Center
University of Wyoming,
Powell, WY

Gary Hergert
Director
West Central Research and Extension Center
University of Nebraska
North Platte, NE