by Antonio Mallarino, Research and Extension agronomist, Iowa State University
Micronutrients are essential plant nutrients that are utilized by crops for physiological processes in very small amounts. Soybean producers and crop advisors have been seeking current, reliable information about micronutrients out of concern that new high-yielding soybean may create deficiencies in the soil.
The amount of micronutrients in soil is determined by the mineralogy of the soil parent material and its organic matter content. Elements considered micronutrients include boron (B), chlorine (Cl), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdeum (Mo), nickel (Ni), and zinc (Zn).
With checkoff funding provided by the North Central Research Program, a team of soybean agronomists and soil fertility experts have been working together to summarize existing knowledge about micronutrient management in the region and determining those areas in which information is weak or not reliable. In addition to reviewing published information, the team studied results of over 200 field trials from ongoing projects since 2012 in Iowa, Minnesota, Kansas, Wisconsin and Indiana.
The research and general management guidelines are summarized in the publication “Micronutrients for Soybean Production in the North Central Region
” (CROP 3135). It is the first regional publication with a thorough discussion of micronutrient needs for soybean based on information compiled from response-based field studies throughout the North Central region. It includes a thorough discussion on the value of soil and plant tissue analyses to determine micronutrient needs. Here are some of the results:
• Micronutrient deficiencies in soybean in the North Central region are uncommon except for iron and manganese in certain soils. Most soils have naturally adequate levels of crop-available micronutrients and some fertilizers, manure, and other amendments contain micronutrients.
• Although high-yielding soybean can remove high amounts of micronutrients, the yield level and yield potential are not good indicators of the need for fertilization with micronutrients.
• Yield increase from micronutrient fertilization is unlikely except for areas with specific soil or environmental conditions that favor deficiency of a specific micronutrient.Soil properties and environmental conditions in which a deficiency is
more likely for several micronutrients in the North Central region
• Soybean iron deficiency is commonly observed in calcareous soils present mainly in western areas of the region. The use of tolerant varieties and recently developed fertilizers are good options to alleviate the impact of iron deficiencies, although typically the yield level achieved is less than in field areas that are not calcareous.
• Manganese deficiency in soybean is observed mainly in coarse textured soils or in certain soils, typically with high pH and organic matter, in Indiana, Michigan, and Ohio. In these soils and conditions, manganese fertilization is a recommended practice.
• Developing interpretations for soil or tissue tests that could guide fertilization for some micronutrients have been difficult because of a lack of widespread micronutrient deficiencies that are essential for test calibrations. Also, the plant-availability of some micronutrients, mainly B, Fe, and Mn, is greatly affected by short-term changes in environmental conditions that are difficult to predict.
• The work demonstrated an urgent need for field calibration research in areas of the North Central region where deficiencies are likely in order to develop more reliable test interpretations.
• Decisions about micronutrient fertilization for soybean should consider soil or tissue test results, but also should consider the soils and environmental conditions that traditionally have been identified with a higher likelihood of deficiencies and economic yield response to fertilization. These include mainly coarse textured, calcareous, organic, or severely eroded soils.
Read the full report: Micronutrients for Soybean Production in the North Central Region - North Central Soybean Research Program and Iowa State University Extension, 2017