Micronutrients are essential plant nutrients that are found in trace amounts in tissue, but play an imperative role in plant growth and development. Without these nutrients, plant nutrition would be compromised leading to potential declines in plant productivity. Of the 17 elements essential for plant growth, eight are micronutrients: boron (B), chlorine (CI), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn) and nickel (Ni).
There is increasing interest from the agricultural community in micronutrient fertilization for a variety of reasons, including: soil erosion and long-term cropping have resulted in the removal of micronutrients from soils; increasing crop yields generally leads to greater micronutrient removal rates in grain and other harvested products; and the widespread replacement of micronutrient-rich manures with mineral fertilizers has reduced micronutrient addition from fertilizer sources. Collectively, these factors have led farmers to question whether micronutrient fertilization may now be required to meet the changing demands of crop nutrition.
The Tri-State Fertilizer Recommendations state that, in general, soils in Michigan, Indiana, and Ohio have adequate amounts of micronutrients to support crop growth. The only reported micronutrient deficiencies in this region have been with B, Cu, Mn, and Zn. These deficiencies can cause plant abnormalities, reduced growth, and sometimes yield losses. The conditions under which micronutrient deficiencies are most likely to occur have been identified for the Tri-State region (Table 1).
|Table 1. Crop and Soil Conditions Under Which Micronutrient Deficiencies May Occur.|
|Boron (B)||Sandy soils or highly weathered soils low in organic matter||Alfalfa and clover|
|Copper (Cu)||Acid peats or mucks with pH < 5.3 and black sands||Wheat, oats, corn|
|Manganese (Mn)||Peats and mucks with pH > 5.8, black sands and lakebed/depressional soils with pH > 6.2||Soybean, wheat, oats, sugar beets, corn|
|Molybdenum (Mo)||Acid prairie soils||Soybean|
|Zinc (Zn)||Peats, mucks, and mineral soils with pH > 6.5||Corn and Soybean|
|Source: Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1995. Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa.|
Diagnosing Micronutrient Deficiencies
There is a large degree of uncertainty in using soil tests for monitoring soil micronutrient levels, as crop micronutrient availability is determined by complex interactions among soil pH, organic matter level, and environmental factors. The Tri-State Fertilizer Recommendations state that plant tissue analysis is useful in determining when plants may be deficient in a particular micronutrient. Tri-State established tissue nutrient sufficiency ranges for agronomic crops are provided in Table 2.
|Table 2. Micronutrient Sufficiency Ranges for Corn, Soybeans, Alfalfa, and Wheat.|
Ear leaf sampled at initial silking
Upper fully developed trifoliate sampled
prior to initial
Top 6 inches
sampled prior to initial flowering
Upper leaves sampled prior to initial bloom
----------------------------------- parts per million (ppm) -----------------------------------------
|Manganese (Mn)||20 – 150||21 – 100||31 – 100||16 – 200|
|Iron (Fe)||21 – 250||51 – 350||31 – 250||11 – 300|
|Boron (B)||4 – 25||21 – 55||31 – 80||6 – 40|
|Copper (Cu)||6 – 20||10 – 30||11 – 30||6 – 50|
|Zinc (Zn)||20 – 70||21 – 50||21 – 70||21 – 70|
|Molybdenum (Mo)||–||1.0 – 5.0||1.0 – 5.0||–|
|Source: Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1995. Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa.|
For soil testing, the Tri-States recommend using different extractants depending on the micronutrient of interest, such as 0.1 N HCl for Mn and Zn and 1.0 N HCl for Cu (Vitosh et al., 1995). However, in the Tri-State region, the Mehlich-3 extractant is most commonly used by commercial soil testing laboratories since it can estimate nutrient availability of multiple elements in a single extraction. But how effective the “universal” Mehlich-3 extraction is at characterizing soil micronutrient availability is not well understood, as recommended micronutrient concentration ranges based on the Mehlich-3 extraction have not been developed for the Tri-State region. Recently, extensive efforts were made to field calibrate Mehlich-3 and DTPA extractants to micronutrient yield response in soybeans and determine which extractant was better able to predict micronutrient deficiency in the Midwest (Mallarino et al., 2017). The results were inconclusive as very few grain yield responses to micronutrient fertilization were observed. The lack of yield responses in micronutrient fertilization trials is a major limitation to developing soil test extractants that can predict micronutrient deficiencies.
Micronutrient Fertilizer Trials in Ohio: 1976 to 2017
Over the past 40 years, there have been ongoing efforts to evaluate the effect of micronutrient fertilization on field crop yields. Here we have compiled all available studies conducted by Ohio State University which examined the effect of micronutrient fertilization on field crop yields in Ohio. We found a total of 194 trials that tested a micronutrient fertilized treatment (or set of treatments) relative to an unfertilized control treatment. Five micronutrients were evaluated independently (B, Cu, Mn, Mo, or Zn) in these trials, while some of these trials evaluated a combination of micronutrients. There was a total of 17 alfalfa trials, 33 corn trials and 144 soybean trials (Table 3). These field trials were conducted in a total of 17 Ohio counties (Figure 1).
|Figure 1. Ohio counties and total number of micronutrient trials (1976-2017).|
In general, micronutrient fertilization rarely resulted in a statistically significant yield response (Table 3). Out of 194 trials, soybean grain yield was responsive to Mn in 6 out of 109 trials and to a blend of Mn and sulfur (S), Mn and B, and Mn and Zn in three out of 23 trials. Boron fertilization had no effect on corn grain yield in 8 out of 9 trials and actually decreased yield in one trial. Across all 33 corn trials, micronutrient fertilization increased yield by less than 1 percent while alfalfa yield decreased by less than 1 percent across 17 trials. Micronutrient fertilization increased soybean grain yields slightly more than 1 percent across 144 trials. Appendix 1 lists all 194 trials evaluating micronutrient fertilization and percent yield response to the fertilizer treatments.
|Table 3. Number of Micronutrient Fertilizer Trials and Yield Response (%) to Fertilization for Alfalfa, Corn, and Soybean Grown in Ohio from 1976 to 2017. Number of responsive trials to micronutrient fertilization shown in parentheses.|
|Manganese (Mn)||3||1||109 (6)||-2.6||0.8||1.4|
|Micronutrient Blend||1||19||23 (3)||5.3||0.9||4.3|
|Source: Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1995. Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa, Table 23. Extension Bulletin E-2567.|
Recent Micronutrient Fertilization Work in Ohio
Three recent studies in Ohio have examined response to micronutrient fertilization in corn and soybean. The first study evaluated soybean response to Mn in 16 paired trials (32 total trials) across 10 counties in 2013 and 2014 (Bluck et al., 2015). Manganese was foliar fertilized with and without a suite of other practices (Rhizobia inoculant, gypsum, insecticide, and fungicide). Soybean was responsive to Mn fertilization in only 1 out of 32 trials. The responsive field was sandy and dry, conditions conducive to Mn deficiency. In a second study with soybeans in two counties in 2014 and 2015, two types of Mn foliar fertilizer treatments (Mn-EDTA and Mn-sulfate), were applied to 6 to 8 soybean varieties after the R2 growth stage (Alt et al., 2018). The Mn-sulfate treatment yielded an increase of 2 bushels per acre compared to the unfertilized control in Wood County in 2014, but no other treatments increased grain yield at any other locations.
The third study conducted in 2015 and 2016 evaluated broadcast and foliar application of micronutrient fertilizers applied to corn and soybean in Clark, Wayne, and Wood counties. In 2015 a micronutrient granular blend containing B, Cu, Fe, Mn and Zn was broadcast-applied at planting. In 2016, the same broadcast application was made, but in separate plots, a micronutrient solution containing B, Cu, Fe, Mn and Zn was foliar-applied at V5 in corn and soybean. Micronutrient fertilization of these crops did not result in a grain yield response at any site and so the measured plant tissue micronutrient concentrations were deemed adequate, that is within the sufficiency range for corn and soybean (Table 4).
|Table 4. Corn and Soybean Tissue Ranges at Three Development Stages Across Three Sites Over Two Years. These crops were not responsive to micronutrient (B, Cu, Fe, Mn, and Zn), so these ranges should be considered adequate for micronutrient needs.|
|Crop||Plant part (Stage)||Boron||Copper||Iron||Manganese||Zinc|
|------------------- part per million (ppm) -------------------|
|Corn||Whole young plant (V5)||16 – 32||3 – 17||109 – 800||15 – 111||20 – 63|
|Ear leaf at silking (R1)||10 – 44||6 – 19||87 – 448||16 – 86||14 – 45|
|Harvested grain (R6)||3 – 10||1 – 4||9 – 49||3 – 8||10 – 36|
|Soybean||Whole young plant (V5)||37 – 74||3 – 37||238 – 2800||24 – 170||17 – 80|
|Upper trifoliate at flowering (R1)||45 – 100||6 – 18||83 – 384||22 – 124||18 – 76|
|Harvested grain (R8)||25 – 52||11 – 24||49 – 107||18 – 42||26 – 50|
|Source: Culman, 2015 & 2016. Soil Amendment and Foliar Application Trials, extension.agron.iastate.edu/compendium/index.aspx.|
Summary and Conclusions
This historical summary of micronutrient trials in Ohio demonstrates that yield responses to micronutrient fertilization are not common. In fact, the only responses observed with micronutrient fertilization occurred when Mn was applied to soybean (9 out of 144 trials). While infrequent, it is important to keep in mind that probability of a yield response to micronutrients is much greater in scenarios where deficiencies are known, or suspected to be more prevalent, for example, in sandy, acidic or peat soils (Table 1).
The infrequency of yield responses to micronutrient fertilization in Ohio has limited the development of reliable soil and plant tissue tests as diagnostic tools that can accurately predict when to apply micronutrient fertilizer. Accordingly, farmers should use all available tools to monitor micronutrient availability in their fields including: scouting for visual deficiency symptoms, soil testing and plant analysis, monitoring yield maps and assessing environmental conditions. When considering micronutrient fertilization, it is always a good idea to leave an unfertilized strip as a check or control. This will allow you to compare areas that received a micronutrient fertilizer versus an area that did not. Yield monitors or weigh wagons can help you determine if the micronutrient fertilization increased yield and provided an economic benefit.
References and Additional Reading
Alt, D., Ng, S.J., Grusenmeyer, J., Lindsey, L.E. 2018. Seed Yield and Quality of Transgenic High Oleic and Conventional Soybean as Influenced by Foliar Manganese Application. Crop Science 58: 874-879.
Bluck, G.M., Lindsey, L.E., Dorrance, A.E., Metzger, J.D. 2015. Soybean Yield Response to Rhizobia Inoculant, Gypsum, Manganese Fertilizer, Insecticide, and Fungicide. Agronomy Journal 107: 1757-1765.
Culman, S.W. Soil Amendment and Foliar Application Trials, 2015 & 2016, extension.agron.iastate.edu/compendium/index.aspx
Mallarino, Antonio P., Kaiser, Daniel E., Ruiz-Diaz, Dorivar A., Laboski, Carrie A.M., Camberato, James J., Vyn, Tony J. 2017. Micronutrients for Soybean Production in the North Central Region. Iowa State University Extension and Outreach. store.extension.iastate.edu/product/15259
Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1995. Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa. Extension Bulletin E-2567. agcrops.osu.edu/publications/tri-state-fertility-guide-corn-soybean-wheat-and-alfalfa
Appendix 1: Compilation of 194 micronutrient yield comparisons conducted in Ohio from 1976 - 2017. Bolded values with an asterisk indicate trials where fertilization statistically increased or decreased yield.
|Crop Yield1||Percentage Yield
|1981a||Wayne||Alfalfa||B, Cu, Mn, Mo, Zn||Soil||3.6||3.8||5.3|
|2000b||Fulton||Soybean||S & Zn||Foliar||197.5||195.2||-1.2|
|2009b||Wood||Soybean||Mn & S||Foliar||53.4||59.7||11.8*|
|2011b||Wood||Soybean||Mn & S||Foliar||76.4||77.1||0.9|
|2012d||Clark||Corn||S & Zn||Soil||220.5||217.3||-1.4|
|2012d||Wood||Corn||S & Zn||Soil||105.9||110.1||4|
|2012d||Wood||Soybean||Mn & S||Soil||63.5||62.7||-1.2|
|2012d||Wood||Soybean||S & Mn, Zn||Soil||63.5||65.2||2.8|
|2012d||Wood||Soybean||S & Zn||Soil||63.5||62.7||-1.3|
|2013d||Clark||Corn||B, S & Zn||Soil||162.4||159.0||-2.1|
|2013d||Clark||Soybean||B & Mn||Soil||55.8||62.7||12.4*|
|2013d||Clark||Soybean||B, S & Mn||Soil||55.8||60.3||8.2|
|2013d||Clark||Soybean||Mn, S & Zn||Soil||55.8||56.7||1.8|
|2013d||Clark||Soybean||Mn & Zn||Soil||55.8||63.1||13.1*|
|2013d||Clark||Soybean||S & Zn||Soil||55.8||56.2||0.8|
|2013d||Wood||Corn||B, Cu, S & Zn||Soil||202.3||203.3||0.5|
|2013d||Wood||Corn||B & S||Soil||202.3||194.0||-4.1|
|2013d||Wood||Corn||B, S & Zn||Soil||202.3||213.6||5.6|
|2013d||Wood||Corn||S & Zn||Soil||202.3||200.4||-0.9|
|2013f||Clark||Soybean||S & Zn||Soil||53.8||57.1||6.1|
|2014d||Clark||Corn||B, S & Zn||Soil||180.7||189.2||4.8|
|2014f||Clark||Corn||S & Zn||Soil||167.7||165.4||-1.4|
|2014f||Clark||Soybean||Mn & S||Soil||53.4||56.7||6.2|
|2015f||Clark||Corn||S & Zn||Soil||140.9||162.7||-15.5|
|2015f||Clark||Soybean||Mn & S||Soil||54.5||58.3||-7|
|2015h||Clark||Corn||B, Cu, Fe, Mn, Zn||Soil||173.7||155.8||-10.3|
|2015h||Clark||Soybean||B, Cu, Fe, Mn, Zn||Soil||63.0||66.7||6|
|2015h||Wayne||Corn||B, Cu, Fe, Mn, Zn||Soil||174.5||186.9||7.1|
|2015h||Wayne||Soybean||B, Cu, Fe, Mn, Zn||Soil||42.1||42.3||0.6|
|2015h||Wood||Corn||B, Cu, Fe, Mn, Zn||Soil||128.4||131.4||2.3|
|2015h||Wood||Soybean||B, Cu, Fe, Mn, Zn||Soil||42.4||46.4||9.2|
|2016f||Clark||Corn||S & Zn||Soil||208.2||202.5||2.7|
|2016f||Clark||Soybean||Mn & S||Soil||63.6||61.2||3.8|
|2016h||Clark||Corn||B, Cu, Fe, Mn, Zn||Soil & Foliar||223.7||232.2||3.8|
|2016h||Clark||Soybean||B, Cu, Fe, Mn, Zn||Soil & Foliar||71.2||71.4||0.3|
|2016h||Wayne||Corn||B, Cu, Fe, Mn, Zn||Soil & Foliar||105.7||105.8||0.1|
|2016h||Wayne||Soybean||B, Cu, Fe, Mn, Zn||Soil & Foliar||37.4||41.4||10.8|
|2016h||Wood||Corn||B, Cu, Fe, Mn, Zn||Soil & Foliar||181.2||188.3||3.9|
|2016h||Wood||Soybean||B, Cu, Fe, Mn, Zn||Soil & Foliar||67.1||67.6||0.7|
|2017f||Clark||Corn||Mn & S||Soil||233.2||222.8||-4.5|
|2017f||Clark||Soybean||S & Zn||Soil||56.7||58.1||2.5|
- Corn and soybean grain yields are in bushels/ acre; alfalfa forage yields are in tons/ acre.
- The difference between the unfertilized and fertilized crop yield as a percentage of the unfertilized crop yield
- Jay Johnson Soil Fertility Research Reports, 1976 to 1993, OARDC.
- Ohio State University Ag Crop Team On-Farm Research Reports, 1999 to 2009, authors: Bruynis, C.; Ruhl, S. D.; LaBarge, G.; Clevenger, B, Wm.; Kleinschmidt, A.; Prill, G.; Sundermeier, A.; Johnson, J. T. agcrops.osu.edu/on-farm-research
- Diedrick, Keith A. Ohio State University PhD Dissertation, 2010. Field Investigations of Nitrogen Fertility on Corn and Soybeans and Foliar Manganese-Glyphosate Interactions on Glyphosate-Tolerant Soybeans in Ohio; rave.ohiolink.edu/etdc/view?acc_num=osu1281988981
- Dygert, C. Mosaic Field Study, unpublished data.
- Bluck, G.M., Lindsey, L.E., Dorrance, A.E., Metzger, J.D. 2015. Soybean Yield Response to Rhizobia Inoculant, Gypsum, Manganese Fertilizer, Insecticide, and Fungicide. Agronomy Journal 107: 1757-1765.
- Watters, Harold. Nutrient trials, unpublished data.
- Alt, D., Ng, S.J., Grusenmeyer, J., Lindsey, L.E. 2018. Seed Yield and Quality of Transgenic High Oleic and Conventional Soybean as Influenced by Foliar Manganese Application. Crop Science 58: 874-879.
- Culman, S.W. Soil Amendment and Foliar Application Trials, 2015 & 2016, extension.agron.iastate.edu/compendium/index.aspx
- Custer, S and Culman, S.W. Tri-State Fertilizer Recommendations Update Project, unpublished data.