Ontario Corn and Soybean Micronutrients Knowledge Hub

This Ohio State Agronomic Crops Network article addresses whether corn starter fertilizers need added micronutrients (B, Cl, Cu, Fe, Mn, Mo, Ni, Zn). Most Ohio soils already supply adequate micronutrients for corn, provided soil pH is properly limed and organic matter is not low on sandy soils. The only micronutrient with a defined response threshold is zinc: a yield response is expected only when soil pH is above 6.6 AND soil-test zinc is below 4 ppm; recommended Zn rates are referenced from the Tri-State Fertilizer Recommendations bulletin. For all other micronutrients, including boron, there is no documented history of deficiency or research-confirmed yield response in Ohio corn on mineral soils; boron interest arose during a period of high corn prices without supporting evidence, and boron response in the region has only been shown for alfalfa on sandy, weathered, low-organic-matter soils. Recommendation: if a micronutrient deficiency has never been confirmed for a field (via soil test and/or visual symptoms), including it in a starter blend is unnecessary and will not improve profitability; the added cost is better spent elsewhere. If a micronutrient is genuinely needed, a starter band placement is the most efficient delivery method. The bottom line: growers should not add micronutrient packages to corn starter fertilizer based on marketing or commodity price alone, only based on confirmed field-specific deficiency evidence.

This Penn State Extension article explains routine mid-season tissue testing to detect micronutrient sufficiency in corn and soybean before deficiencies become visible ("hidden hunger"). Soil tests are considered unreliable for micronutrients such as iron, zinc, manganese, boron, and copper, making tissue testing especially useful for these elements. Sampling: for corn, collect the ear leaf at silking; for soybean, clip the uppermost fully-developed trifoliates prior to or at early flowering (sampling after pod set is not recommended). Take at least 10, preferably 20-30, plants per field/sub-field, avoid diseased, pest-damaged, drought-stressed, or flooded tissue, and ship samples in breathable paper bags to prevent mold. Reported sufficiency ranges (ppm) for corn ear leaf: manganese 20-150, iron 20-250, boron 4-25, copper 6-20, zinc 20-70. For soybean uppermost leaves: manganese 21-150, iron 50-350, boron 20-50, copper 10-30, zinc 20-50. Values above range are not yield-limiting but may signal other fertility issues (e.g., high iron/manganese can indicate low soil pH). Values below range indicate the nutrient may be yield-limiting. For corn, rescue applications at silking are often impractical due to sprayer clearance; soybean, being shorter and more plastic in growth, can more feasibly receive foliar rescue micronutrient applications since only small doses are needed. Even without a rescue treatment, a low result flags problems to address via soil testing before the next season, since tissue levels reflect uptake, not necessarily true soil deficiency.

Soybean is widely used as food. Genetic factors, as well as agrotechnical procedures, affect the yield and quality of soybeans. The subject of our research was the synchronization between soil N supply (from both mineralization and fertilization) and crop N demand. The aim of the research was to determine the effect of the cultivar and nitrogen application on the seed yield and mineral content in soybeans. Two non-GMO soybean cultivars (Amandine and Merlin) and four mineral nitrogen fertilizers ((A) N 0, control; (B) N 30:0, 30 kg N ha-1 before sowing; (C) N 0:30, 30 kg N ha-1 at BBCH 73-75; (D) N 30:30, 30 kg N ha-1 before sowing and 30 kg N ha-1 at BBCH 73-75) were tested. The highest soybean yield was obtained following nitrogen application at a rate of 60 kg ha-1. The genetic factor was found to significantly influence the content of some macronutrients (P, K, and Mg) and micronutrients (Cu, Mn, and Fe). In general, the Merlin cultivar had better macronutrient parameters except nitrogen, while Amandine had a higher content of Cu and Fe. Nitrogen fertilization decreased the content of P, K, and Zn in the soybeans but significantly increased the content of Ca, Mg, Cu, and Mn.

Because of low content of available iron (Fe) in soils and its poor mobility in plants, iron fertilization is necessary. Different forms of iron (mineral salts, chelates, nanomaterials) and fertilization strategies (soil and foliar application of solid or liquid fertilizers) are used. The effect of solid mineral fertilizers (A: a mixture of ammonium nitrate and dolomite; B: a mixture of ammonium nitrate and sulfate) enriched with iron sulfate was assessed during a three-year pot experiment. Iron addition did not change the yield of spring rape (first year) or maize (second and third year) significantly, and the effect on iron content in the plants was ambiguous. Fertilizer B with iron had the greatest yield-forming effect, increasing the yield of aboveground parts by 355?874%, and of roots by 211?692% in particular years. All fertilizers (especially containing sulfur) acidified the soil. After the experiment, pH of the soil fertilized with sulfur was 4.1, and of the unfertilized soil ? 5.2. Iron addition increased the content of mobile and exchangeable iron in the soil by 12?110% and 2?58%, respectively, but not the content of the fraction bound to MnOx. Combination of sulfur and iron fertilization has a potential to improve soil abundance and plant yield.

Background: Low soil temperature in spring is a major constraint for cultivation of tropical crops in temperate climates, associated with impaired seedling development, inhibition of root growth and root activity. In this study, potential cold-stress protectants, such as supplemented micronutrients (Zn, Mn), seaweed extracts, and rhizobacteria with plant growth-promoting potential (PGPRs) were tested in order to improve the tolerance of maize to low root zone temperatures (RZT) during early growth. Methods: Maize (v. Colisee) was cultivated in a root cooling system for adjustment of the RZT. In three independent experiments, after germination at 20 degrees C, the cold-stress phase (12-14 degrees C) started at 14 days after sowing to simulate a cold period in spring. Micronutrients, seaweed extracts, and PGPRs were supplied by fertigation (experiment 1), fertigation and seed dressing (experiment 2), and nutrient seed priming (experiment 3). At the end of the experiments, scoring of oxidative leaf damage, biomass production, chlorophyll status (SPAD), root length density, superoxide dismutase activities in leaf and root tissues, and the shoot mineral-nutritional status were determined. Results: Positive effects on plant growth and particularly on root development at low RZT were detected exclusively for seaweed extracts with high Zn/Mn contents and similar growth promotions were induced by Zn and Mn application in comparable amounts. This finding suggests that the selected seaweed extracts were mainly acting via improved Zn and Mn supply to the plants. It was essential that the cold-stress protectants were present during seed imbibition. The beneficial effect of Zn/Mn treatments and sea weed extracts was associated with increased superoxide dismutase activity in the root and leaf tissue, with key functions in antioxidative stress defense, depending on Zn, Mn, Cu, and Fe as enzymatic co-factors. Accordingly, leaf damage, shoot and root growth inhibition in cold-stressed plants was associated with a low Zn-nutritional status, mitigated by application of the cold-stress protectants. Conclusions: Since micronutrients are effective already at low concentrations, starter applications of Zn/Mn or the respective seaweed extracts may offer an economic option for cold-stress prophylaxis in crops.

High soil pH can lead to Mn2+ and P deficiency and yield losses. In addition, it is unclear which process, nitrification-induced acidification of bulk soil or nitrification inhibitor-driven rhizosphere acidification, is more effective in increasing Mn2+ availability and shoot concentration. Thus, this topic was investigated in this study. Moreover, we also evaluated if applying NIs can avoid P deficiency in soil with high pH and high buffering capacity. Two greenhouse experiments were carried out to investigate the impact of applying 3,4 Dimethylpyrazole phosphate (DMPP) in sandy soil subjected to the application of different lime rates, simulating several soil pH and buffering capacity conditions. The utilized lime rates were 0, 0.5, 1, 2 and 4 g CaCO3 kg?1. The measured variables were bulk and rhizosphere soil pH, Mn2+ and P availability, maize biomass production, as well as Mn and P shoot concentrations. DMPP significantly reduced shoot biomass by 10% in unlimed soil; however, it promoted the overall shoot biomass by 30% in limed soil in both experiments. In addition, DMPP decreased the overall Mn shoot concentration by 24 and 21% in experiments I and II, respectively. In contrast, DMPP increased the overall P shoot concentration due to rhizosphere acidification by 24 and 17% in experiments I and II, respectively. The DMPP application did not avoid P deficiency under the highest lime rate (4 g CaCO3 kg?1) despite alleviating it. In conclusion, the application of NIs is not beneficial for increasing Mn2+ shoot concentration and, when performed to increase P availability in high pH soils, should consider the likelihood of causing Mn deficiency.

This UMN Extension article covers manganese (Mn) management for Minnesota crops, with soybean and corn as the relevant row crops (soybean is high-sensitivity, corn is low-sensitivity to Mn fertilization). Mn deficiency is more likely on heavily weathered sandy or organic soils with pH above 6.0 (mineral/calcareous soils above 6.5); toxicity can occur below pH 5.0. Deficiency causes interveinal chlorosis in young leaves (soybean: chlorotic between green veins, browning/death in severe cases; corn: interveinal chlorosis with stunting and white leaf flecks in severe cases). Diagnosis uses soil testing (DTPA method recommended; Mehlich-III not correlated with DTPA and not interchangeable) plus tissue testing (sufficiency ranges: soybean 17-100 ppm in most recently matured trifoliate leaves at early flowering; field corn 15-150 ppm in ear-leaf-base leaves at initial silk). However, DTPA soil test is not calibrated for Minnesota agronomic crops, so no soil fertilizer recommendations are provided for grain crops. Minnesota field trials (2011-2014, 18 soybean sites; 2011-2013, 8 corn sites) found Mn fertilization did not significantly increase tissue Mn or grain yield at any location for either crop, even where trifoliate Mn was above the sufficiency range. Bottom line: the University of Minnesota does not recommend Mn fertilization for any Minnesota field crop (only for sensitive vegetables on organic soils). If deficiency symptoms are suspected, confirm with both soil and tissue tests before treating, and report cases to the UMN nutrient management team. Note: foliar Mn can antagonize glyphosate efficacy in tank mixes; use chelated Mn-EDTA to reduce this interaction.

Iron deficiency chlorosis (IDC) in soybean results in yield losses or in extreme cases death. Breeding for resistance has shown limited success with no cultivar having complete resistance. Mineral content of the soybean could be an indicator of the ability of the plant to withstand the effects of IDC. Iron (Fe) and zinc (Zn) concentration was examined in soybean seed and leaves. SSR, RFLP, and BARCSOYSSR markers were used to construct a linkage map used for mapping of Fe and Zn concentrations. The QTL analysis for the combined data identified one major QTL for seed Fe accumulation on chromosome 20 that explained 21.5% of the variation. This QTL was in the marker interval pa_515-1-Satt239, with marker pa_515-1 previously being used to map an Fe-efficiency QTL. This provides the first evidence of a potential genetic link between Fe-efficiency and Fe accumulation in the soybean seed.

This UMN Extension guide addresses iron deficiency chlorosis (IDC) in soybean, common in South Central, Southwest, West Central, and Northwest Minnesota. IDC appears as interveinal yellowing with green veins, caused by insoluble Fe(III) in high-pH, high-calcium-carbonate soils; soybean (a Type I plant) relies on root-excreted acids/reductants to convert Fe(III) to soluble Fe(II). Severity increases with high lime, wet/cold soils (bicarbonate buildup), fresh organic matter, and high soil nitrate (nitrate uptake raises leaf pH, reducing Fe reduction). Recommended management, ranked by cost-effectiveness: (1) Select an IDC-tolerant variety - the single most beneficial practice, with yield differences of up to 10 bu/acre between tolerant and susceptible varieties under high IDC pressure; (2) Seed-place an ortho-ortho EDDHA iron chelate (e.g., Soygreen) at 1-3 lb product/acre, which reliably increased yield (up to 20 bu/acre in trials) - only the o-o-EDDHA form is stable enough at high pH to be effective; other Fe products and placements gave inconsistent results; (3) Increase seeding rate, which modestly reduces IDC severity and can improve net return, especially for tolerant varieties in severe-IDC areas; (4) Use an oat companion crop (seeded ~1.5 bu/acre) to draw down soil nitrate and moisture, requiring termination by 10-12 inches height - the least beneficial of the four practices economically. Additional stress reduction (avoiding injurious herbicides, minimizing compaction, managing SCN and disease) also helps. Practices can be combined but need not all be used; growers should tailor selection to field risk and management capacity. Soil Fe tests are not useful for predicting high-lime IDC.

Maize (Zea mays L.) yields have advanced through breeding complemented with evolving management technologies including plant density (PD) and macronutrient fertilizer inputs. Little is known about management-induced changes in plant uptake or allocation of nutrients other than macronutrients. Therefore, impacts of both PD and N rate at three levels (low, medium, and high) on Ca, Mg, and micronutrient partitioning (for pertinent plant organs at six growth stages) were investigated at four environments in Indiana. Grain Ca, Mg, Fe, and Zn contents at maturity were primarily influenced by N rate, while the PD × N rate interaction influenced those of Mn and Cu. At the whole-plant scale, PD and N rate significantly influenced all nutrient contents, and vegetative-stage nutrient accumulation averaged 91% (Ca), 51% (Fe), 47% (Zn), and 73% (Mn, Mg, and Cu) of corresponding nutrient contents at maturity. During the vegetative phase, three modes of leaf vs. stem nutrient partitioning were: (i) preferential allocation of Mg and Zn to stems; (ii) preferential allocation of Fe and Ca to leaves; and (iii) isometric partitioning of Cu and Mn. Isometric nutrient concentration patterns between Mg and Zn were documented in leaf, stem (vegetative phase), and ear (reproductive phase). Early-reproductive-stage nutrient partitioning from plant to ear was greatest for Zn and Mg and mirrored their respective harvest indices (HIs) at maturity. Nutrient HIs, concentrations (grain + stover), and internal efficiencies at maturity were positively impacted by N rate but negatively by PD. Reliable micronutrient requirement estimations for maize under diverse management and yield levels help inform future balanced-nutrient input decisions.