Search
David Moseley, Rasel Parvej, Syam Dodla, Jim Wang, LSU AgCenter Scientist
Iron is an important element for several plant functions such as chlorophyll synthesis, photosynthesis, and respiration. If plants are deficient in iron, the symptoms begin as interveinal chlorosis in the younger leaves (Figure 1). If the deficiency is severe, the symptoms can be white or necrotic leaves (figure 2).
Figure 1. Soybean leaves showing iron deficiency chlorosis symptoms
Figure 2. Soybean leaves showing severe iron deficiency chlorosis symptoms.
The conditions that promote iron deficiency chlorosis include high pH soils (>7.0) with high carbonates and soluble salt content. Other conditions that increase the probability of iron deficiency chlorosis include cooler temperatures, saturated soil, high amounts of available nitrates, and compacted soil conditions. In addition, excess soil content of other nutrients including copper, manganese, zinc, and molybdenum can limit iron uptake. The iron deficiency chlorosis symptoms will often be randomly scattered based on differences in soil conditions throughout the field (Figures 3 and 4).
Figure 3. Soybean plants at the V3-V4 growth stage are showing symptoms of iron deficiency chlorosis in random spots throughout a field. This picture was taken on May 5, 2022.
Figure 4. Soybean plants at the V3-V4 growth stage that are showing various degrees of iron deficiency chlorosis within the same row.
The iron deficiency chlorosis symptoms can alleviate if the soil conditions improve and/or if the roots reach a more favorable environment (warmer; less saturation or available nitrates). As the roots grow deeper, the soil can be less alkaline which will allow more available iron content. Soybean plants can show symptoms of iron deficiency chlorosis during early growth stages and become symptom free as the conditions improve (Figures 5 and 6).
Figure 5. Soybean plants at the R3 growth stage. The symptoms of iron deficiency chlorosis shown in figure 3 have decreased. This picture was taken on May 17, 2022.
Figure 6. Soybean plants at the R4 growth stage. The symptoms of iron deficiency chlorosis shown in figures 3 and 5 have completely waned with no noticeable differences throughout the field. This picture was taken on June 3, 2022.
If iron deficiency chlorosis is suspected, tissue and soil test should be taken. Tissue and soil samples should be taken from areas that have symptomatic plants and plants showing no symptoms. This comparison can help determine what the deficiency may be. If any soil residue on the leaf surface contaminates the tissue sample, the collected tissue samples should be rinsed off with deionized water and the excess water should be dried before sending the sample to the lab.
Soybean plants can be sensitive to iron deficiency. However, there are varieties that are tolerant (Figure 6). Tolerance is based on a genetic variation that allows the plant to change the environment around the root by excreting H+ or organic acids and chelating compounds. These excretions from the roots increase the availability and uptake of iron by the plant.
Figure 7. Iron deficiency chlorosis in soybean on high pH soils (~8.0) at the Dean Lee Research Station, Alexandria, LA. There is a noticeable difference in iron deficiency chlorosis symptoms between two varieties. The variety on the left shows more tolerance than the variety on the right. The picture was taken by Dr. Rasel Parvej, State Soil Fertility Specialist, LSU AgCenter.
Other corrective measures include soil application of iron chelate products and foliar applications. These applications may not be necessary in Louisiana since most varieties tested at the Dean Lee Research Station (location where soybean plants historically have shown symptoms of iron deficiency chlorosis) do not show severe iron deficiency chlorosis symptoms and have good yield potential. Therefore, when selecting a soybean variety, look at the yield from the Dean Lee Research Station to see if the variety was competitive. The seed companies may also have an iron deficiency chlorosis tolerance rating.
Experiments conducted by LSU AgCenter scientists at the Red River and Dean Lee Research Stations have shown up to 7% or 4 bu/ac improvement in grain yield with the soil application of iron chelates (Figure 7). In furrow application of iron chelates at 0.25 lb Fe/ ac could be beneficial for the soils with potential iron deficiency chlorosis.
Figure 8: Effect of Iron application (as Fe-EDDHA with 6% Fe) on soybean grain yield at Dean Lee Research Station
