Iron chlorosis with soybean continues to be a major problem for crop procedures in much of western and northwestern Minnesota.  Of course, this is not a new problem.  Soybean producers have struggled with this yield reduction factor for over 25 years.  Many, however, have observed that the problem has become more severe in recent years.  The acreage affected has increased and the yield reduction associated with this problem has become more severe.

Approximately 25 years ago, a consideable amount of research effort was focused on finding an answer to this problem.  Much of the early activity involved a foliar application of various iron materials.  These materials were usually expensive.  Success in correcting iron chlorosis with foliar applications was not consistent and and routine use of this management practice wass not readily adopted.

Within the past three years, there has been a renewed effort to identify management practices that can be used for correction of this problem.  A summary of the progress in these renewed research efforts is provided in the following paragraphs.

Improvement in Varieties

Compared to previous years, there have been major improvements in soybean varieties that are tolerant to soil and environmental conditions that lead to iron chlorosis.   The improved varieties have been the result of both public and private research projects.  As a result of these efforts, varieties are more tolerant and tolerance has been introduced into short season varieties that are needed in northwestern Minnesota.

Selection of a tolerant variety is the first step for the soybean grower who faces the problem of iron chlorosis.  Although the rating systems or scales are not consistent among seed companies, most have their varieties ranked or rated.

Soil Testing is Important

There's been general agreement for several years that iron chlorosis is associated with calcareous soils (pH greater than or equal to 7.4).  As research continues, we've learned that factors other than pH are important.  If soils are calcareaus, a measure of soluble salts and calcium carbonate is important.  As information is collected each year, it appears that a combination of these two measurements will be used to assess the risk of occurrence of iron chlorosis.  At this time, definite guidelines have not been established.  Data from trials in both North Dakota and Minnesota weill be used to establish future guidelines.

Higher Seedling Rates May Help

Various observations by both farmers and researchers have suggested that higher plant populations may help to minimize yield reductions.  Trials conducted in fields with severe chlorosis problems in 2001 suggested that plant populations that were about 15% higher than current recommendations would increase soybean yields.  These results were preliminary and further research is needed.

The availability of Roundup Ready varieties has also allowed growers to try an approach that might be an alternative to increasing the seeding rate.  With this new idea, soybeans are planted with a small grain crop.  During the early part of the growing season, Roundup is used to kill the small grain crop.  Some farmer experiences with this practice suggest that it can increase yields.  Detailed research will be conducted this year to document the value of this practice.

Coating the Seed with Iron

With current technology, it is possible to coat soybean seeds with chelated sources of iron.  Research conducted at the Northwest Research and Outreach Center has shown that use of this practice can have a positive effect on yield.  However, relatively small amounts of iron can be applied in this manner.  There are also major unanswered questions that revolve around iron source and rate of application.  Research conducted in 2001 showed that use of this practice could e a major step forward in overcoming the iron chlorosis problem.  It appears that application of iron in this way only will not be adequate for supplying sufficient iron throughout the growing season.   This management practice will be further evaluated during the 2002 growing season.

Foliar Application

Use of foliar application of iron is not a new concept.  This practice was researched in the past.  In the earlier research, however, the iron was applied when the soybeans showed various stages of severity of chlorosis.  With deficiencies evident, the physiology of the plant was probably severely affected.  As a result, the plant may not have been able to metabolize the applied iron.  Therefore, results were inconsistent. 

Currently, it appears that the combination of iron coated seed and foliar applied iron may provide substantial reduction in the severity of the chlorosis.  The iron coated on the seed may be adequate until the second or third trifoliate.  If plants are not chlorotic at this stage of growth, the foliar application of iron may provide an increase in yield.

There are many questions associated with this combination of practices.  Research planned for 2002 will focus on providing answers to some of these questions.

Soil Applied Iron

The use of iron coated seed and foliar application of iron may not be the only management practices that will reduce the severity of iron chlorosis.  Application of iron with the seed at planting may also be effective.  The iron may be applied as either a fluid or dry material.  Some research conducted in 2000 and 2001 showed that this practice could be effective.  Results, however, have been inconsistent.   This potential management practice will be further evaluated in research planned for the 2002 growing season.

Keep Stress to a Minimum

With recent research activity, it seems that iron chlorosis is more severe when there is added stress on the soybean plant.  Soils with high levels of soluble salts and calcium carbonate are a stressful environment for soybeans.  Since these soil properties cannot be easily altered, it's important to choose a variety that will tolerate these conditions.  Seedling diseases such as pythium and rhizoctonia are also added stress factors when soils are cold and wet.  Treatment of the seed with an appropriate fungicide may help to reduce stress from these diseases.

Use of some herbicides can also add a stress to soybean production.  Several herbicide choices are available to the soybean producer.  Serious consideration should be given to selecting herbicides that are not causing any stress to the soybean crop.

Stay Tuned

Iron chlorosis is a complex problem involving both plant and soil factors.  There are no easy answers.  Research conducted in recent years has provided some important information.  Research planned for 2002 will build on what has been learned from trials conducted in 2000 and 2001.  There has been progress.  We hope that research conducted in 2002 will provide more answers.