Source: Dorivar Ruiz Diaz, Nutrient Management Specialist, Kansas State University

During 2009 and 2010, we conducted tests at seven locations in Kansas with seed coating treatments and foliar iron treatments to correct iron deficiency symptoms in soybean. We used two varieties, one with good iron chlorosis tolerance and one that was susceptible to iron chlorosis. The tests were under irrigated conditions.

The seed coating treatment was approximately 0.3 lb/acre of actual Fe as chelated EDDHA Fe (6%). The foliar treatments were 0.1 lb/acre EDDHA Fe (6%) and 0.1 lb/acre HEDTA Fe (4.5%). There was an untreated check included. Soil pH at these locations varied from 7.9 to 8.4.

Fertilization Strategies for Iron Chlorosis

Greenness. The seed coating treatment had a significant effect in improving the greenness of the foliage, as shown by the chlorophyll meter reading. Overall, the greening response to the seed coating was greater than response to foliar iron applications. The variety most susceptible to iron chlorosis greened up in response to the seed coating much more than the variety more tolerant to iron chlorosis. The tolerant variety stayed greener during the growing season but still showed some additional benefit from the seed coating treatment. The seed treatment also increased plant height by an average of about 5 inches for both varieties (data not shown).

Fertilization Strategies for Iron Chlorosis

Yield. Both the tolerant and susceptible variety also had a good yield response to the iron chelate seed coating, and no significant yield response to the foliar iron chelate treatments. Yield increase due to the seed coating treatment in the susceptible variety was approximately 10 bu/acre, with similar yield increase for the tolerant variety.

Fertilization Strategies for Iron Chlorosis

Summary

  • Foliar Fe treatments to soybeans with iron chlorosis seem to increase the "greenness," but our results suggest that yield increase may be inconsistent in western Kansas. 
  • An iron chelate seed coating provides significant yield increases to soybeans under conditions with severe iron chlorosis issues. Another alternative to seed coating is in-furrow application of chelated Fe fertilizer, which has shown comparable results. Seed contact with the fertilizer source seems to be particularly important for reducing iron chlorosis symptoms. 
  • If iron chlorosis has been a common problem in the past, producers should select a soybean variety that is tolerant to Fe chlorosis. It may also pay to also use a chelated iron in-furrow application, or an iron chelate seed coating. 
  • Producers should avoid excessive application of nitrogen fertilizer to the crop that precedes soybeans in the rotation. In fields with some risk of iron chlorosis, the high levels of soil nitrate may be a complicating factor.

This study is funded by the Kansas Soybean Commission.