Iron deficiency chlorosis (IDC) continues to plague soybean producers in much of Minnesota. Research continues to search for an answer to this problem. In 2004, various management practices were evaluated. The foliar application of various iron materials was one of those practices. A progress report for that research project follows.

The research trial was conducted in the field of a cooperating farmer in Chippewa County. The field had been planted in 30 inch rows to a variety that was advertised as being tolerant to IDC. In mid-June, a large portion of the field showed uniform symptoms of IDC. The soybeans were at the 3 rd to 4 th trifoliate stage of development.

The study was designed to evaluate the use of three iron materials used as a foliar application to supply 0.125, 0.250, 0.375, and 0.500 lb. Fe per acre. Two applications were used with one-half of the Fe applied at each time. The iron materials were ferrous sulfate (FeSO 4), EDDHA iron chelate, and DTPA iron chelate. The FeSO 4 would be the least expensive of the three materials. All materials were applied with a surfactant. An appropriate control (no foliar iron) was used. The first application was made at the 3 rd to 4 th trifoliate stage of development and the second application was made 12 days later.

Whole plant samples were collected from each plot at early bloom. These plants were washed to remove any iron that might have adhered to the plant as a consequence of the foliar application. Following washing, the plants were dried, weighed, ground and analyzed for iron.

Soybean yield was measured in October. All yields were corrected to 13.5% moisture.

Soybean Yield

Measured yields are summarized in Table 1. Even though there were uniform and significant IDC symptoms in mid-June, the soybeans recovered in late summer and yields were not as low as expected. Since the soybeans appeared to be actively growing yet showing IDC symptoms, this was a good situation to evaluate foliar application as a potential management practice.

Compared to the control, there was a small, but consistent, yield increase when foliar iron was used. When averaged over all rates, this increase varied from 2.5 to 3.8 bu. per acre.

Small rates of Fe applied as each of the sources appeared to be adequate for optimum yield. The data are not adequate to identify the most effective and most economical source of iron.

Table 1. Soybean yield as affected by 3 sources of iron applied to supply 4 rates of iron.

Iron Concentration In Plants

The concentration of iron in the whole plants is summarized in Table 2. Compared to the control, iron concentration was increased when ferrous sulfate and iron DTPA were used to supply the iron. There is no easy explanation for the low concentrations associated with the use of the iron EDDHA. The yield increase associated with the use of this source of iron would indicate that some of the applied iron was absorbed by plant.

Table 2. Iron content of soybean plants at early bloom as affected by 3 sources of iron applied to supply 4 rates of iron.

The results of this study are encouraging. They indicate that the foliar application of iron may be of some benefit. These results, however, do not provide the basis for recommendations for foliar use of iron.

Acknowledgement  

The support of this research in dollars provided by the Minnesota Soybean Research and Promotion Council is gratefully acknowledged.

A Call For Help  

Research focused on reducing the severity of IDC will continue in 2005. Cooperation from soybean growers who have fields affected by IDC is needed. I’m looking for fields where research projects can be conducted. Please let me know the location of fields that might be used for this research.

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