Iron Deficiency Chlorosis in Soybean (6/23/11)

Iron Deficiency Chlorosis (IDC) is expressed in new leaf tissue as an interveinal yellowing while the veins remain green.  As the deficiency progresses, leaf tissue and even the growing point can die.  Iron is an essential micronutrient for the plant. Besides being needed in chlorophyll, Fe is also involved in the energy transfer of the plant, is part of certain enzymes, and is needed in the root nodule formation associated the N-fixation.

The effect of IDC is reduced plant growth and can lead to a reduction in yield potential.  Even a temporary yellowing is associated with yield loss. Usually there is abundant iron in the soil in North Dakota and only a small amount is needed by the plant. Iron is rather insoluble and with increased soil pH the solubility becomes even lower. Soils with calcium carbonate (lime) in the topsoil are most prone to produce soybeans with IDC.  However, increased salt concentration, wet conditions, cool temperatures and readily available nitrate near the plant can all interact and aggravate the IDC symptoms.  Compared with other crops soybeans are inefficient in using Fe.  If the deficiency is not too severe, soybeans can grow out of IDC as the conditions improve and the larger root system is able to take up sufficient Fe.

There is a difference in how soybean varieties respond to adverse conditions. In soils with poor drainage, high pH, and salinity issues farmers should have selected the most tolerant soybean varieties available for the maturity zone.  As the crop is already growing and the variety cannot be changed at this time, it would be a good strategy to note which fields show elevated IDC levels and see what the NDSU (IDC) rating is on the presently grown variety. If IDC is an issue, varieties selection based on IDC ratings should be considered in future plantings.  IDC scores for varieties can be found in the NDSU Soybean performance testing results publication A-843 or at http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/a843.pdf

None of the presently grown commercial varieties are completely tolerant against IDC but there are definitely big differences among varieties in their response to IDC. Variety selection is the most important management decision to combat IDC in soybean. Improving internal soil drainage and leaching out of salt may also help to create more favorable growing conditions in future years.

Foliar application of Fe might be an option to consider. Re-greening of the plants is possible and depends on the variety and especially the timing of the application. Early application, even at the first trifoliate growth stage, can be considered. If application is delayed and the symptoms are severe, spraying may not be as effective.  Based on research conducted by Dr. Rehm in Minnesota the results of foliar application of Fe are inconsistent. The cost of the product, application cost, and potential wheel damage due to driving in the crop should be considered when thinking about a foliar application.  If the soybeans are grown in wider rows, 1 or 2 lb/a of FeEDDHA can be applied, with the spray focused narrowly on the rows.  If washed off by subsequent rains, the FeEDDHA has soil activity, unlike most other foliar materials.  However, it is better to prevent chlorosis by planting a resistant variety and using FeEDDHA as a starter fertilizer, than to try to green up a crop after it has turned yellow.

Hans Kandel - Extension Agronomist Broadleaf Crops

hans.kandel@ndsu.edu

Jay R. Goos - NDSU Soil Scientist