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Is a "Bad Chlorosis Year" in Store? (05/30/19)

Things are shaping up for 2019 to be a "bad chlorosis year".

Is a "Bad Chlorosis Year" in Store?

Things are shaping up for 2019 to be a "bad chlorosis year". The greatest factor in the severity of iron deficiency chlorosis, or IDC, in soybeans is the amount of bicarbonate ions in the soil water. Bicarbonate, or HCO3-, is the same ion that is found in sodium bicarbonate, or common baking soda. Bicarbonate accumulates in the water in the topsoil when the following three things occur:

     1- there needs to be lime, or calcium carbonate in the topsoil,

     2- the soil needs to be wet,

     3- there needs to be biological activity to generate carbon dioxide, which generates more bicarbonate.

Bicarbonate interferes with a soybean plant's ability to take up iron and  the plant's ability to move the iron around in the plant. So, with wet conditions, and late planting, 2019 could be a very bad chlorosis year.  

The most effective control measure for IDC is planting a resistant variety. This is not a good year to experiment with a brand-new variety without a local track record on IDC-prone land. It might be a wiser choice to stick with a variety with a good record of IDC resistance. Nothing can substitute for a resistant variety. There is no fertilizer, no foliar spray, nor any other cultural practice that can turn a weak variety into performing like a resistant variety on IDC-prone land. No variety is immune to IDC. Even a resistant variety can turn yellow if conditions are bad enough. So, other cultural practices, like an iron fertilizer, need to be added to a resistant variety, not used instead of a resistant variety. A fertilizer supplier may imply that using a certain fertilizer or amendment will allow a soybean farmer to plant whatever variety they want on IDC-prone land. According to my research, that is not true.

Regarding iron fertilizers, there are three compounds that my research has shown to give at least an early-season reduction in chlorosis. The three "red" chelates, FeEDDHA, FeEDDHSA, and FeHBED, can all reduce chlorosis early in the season. Typically, 2-3 pounds per acre of a 6% a.i. product in-furrow is needed for an early-season response. Commercial iron products vary in quality though. The higher the quality, the longer-lasting the response will be. Products with a lower percentage of the effective isomers need to be applied at higher rates than higher-quality products.

Another cultural practice that is helpful, is increased row spacing and seeding rate.  Going to 22 or 30 inch rows will result in less IDC than planting with narrower rows, in general. However, increasing row width will probably increase weed pressure and will decrease yield in non-IDC areas. Sometimes more than one cultural practice is needed when IDC is severe. I work with a group of farmers in the Colfax, ND, area, and the best results on IDC-prone land are obtained when three cultural practices are combined: a resistant variety, 22 or 30" rows, and an in-furrow application of 3 lb/A of an effective FeEDDHA product.

R. Jay Goos

Soil Science Professor

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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