Ontario Corn and Soybean Micronutrients Knowledge Hub

This Saskatchewan Crop Diagnostic Handbook section covers general soil fertility diagnostics; corn/soybean-specific micronutrient content is limited to a few reference tables and general principles. Nutrient removal/uptake tables give micronutrient removal per bushel of grain: for corn, 0.015 lb B, 0.012 lb Cu, and 0.089 lb Zn (no Mn/Fe values reported); for soybean, 0.174 lb B, 0.075 lb Cu, and 0.22 lb Zn. A general nutrient-properties table lists micronutrient plant-available forms, soil/plant mobility, and typical fertilizer sources: B (H3BO3/BO3-, immobile in plant, very mobile in soil, sources include borax/sodium tetraborate), Cu (Cu2+, immobile in plant and soil, copper sulfate/EDTA chelate), Fe (Fe2+/Fe3+, immobile, ferrous/ferric sulfate), Cl (mobile), Mn and Zn (immobile in plant; Mn mobile in soil, Zn immobile), Mo (mobile). Deficiency symptoms for all micronutrients except Mo and Cl appear first in young/new leaves. Recommendations: the handbook advises that diagnosing micronutrient deficiency from visual symptoms alone is difficult even for trained agronomists, and multiple lines of evidence ? field symptoms, plant tissue tests, soil tests, comparative unaffected-vs-affected sampling, test strips, and cropping history ? should be combined before recommending a micronutrient application, since a single indicator is not considered reliable. Soil pH strongly influences availability: strongly alkaline soils reduce the relative availability of iron, manganese, copper, and zinc, so pH should be checked alongside nutrient testing when deficiency is suspected. The handbook does not provide crop-specific application rates, thresholds, or corn/soybean deficiency symptom descriptions beyond these general principles; growers are directed to submit paired soil/tissue samples from affected and unaffected field areas to a testing laboratory for a definitive diagnosis rather than relying on visual assessment alone.

Background: Soybean iron deficiency chlorosis (IDC) is an important nutrient stress frequently found in high pH and/or soils high in calcium carbonates. To advance the understanding of IDC resistance in soybean, a rapid (21-day) controlled-environment assay was developed to investigate the effects of nodulation, pH, and calcium carbonate levels on soybean iron deficiency traits. This system was tested on four genotypes known to exhibit differences in iron efficiency, including two standard IDC check cultivars and a pair of near-isogenic lines exhibiting variation at an IDC resistance quantitative trait locus. Visual score, chlorophyll content, plant height, root dry mass, and shoot dry mass were measured to quantify iron stress. Results: Calcium carbonate levels and nodulation were found to have the greatest effects on IDC severity. Increasing calcium carbonate levels worsened IDC symptoms, while nodulation reduced symptoms in all genotypes. Higher pH levels increased iron deficiency symptoms in check genotypes 'Corsoy 79' and 'Dawson', but did not induce iron deficiency symptoms in near-isogenic lines. A significant interaction was observed between genotype, nodulation, and calcium carbonate level, indicating that a specific treatment level could discern IDC symptoms between genotypes differing in resistance to IDC. Conclusions: IDC symptoms were successfully induced in the Check Genotypes Experiment as well as the NIL Experiment, indicating the success of using this assay for inducing IDC in controlled environments. However, our results suggest that treatment levels that best differentiate genotypes for their IDC resistance may need to be determined for each experiment because of the unique way in which different genotypes display symptoms and respond to iron deficiency conditions. Core ideas: An assay was developed to independently assess factors leading to IDC in soybean. Calcium carbonates have a greater influence on IDC symptoms than pH. Nodulation improved resistance to IDC in highly resistant and low resistant soybean genotypes. The developed assay is highly sensitive and can detect slight differences in IDC resistance.

This Iowa State Integrated Crop Management blog (2024) addresses whether growers need micronutrients in their soil fertility program for corn and soybean. Micronutrients (B, Cl, Co, Cu, Fe, Mn, Mo, Ni, Zn) are needed in very small amounts (usually 1-3 lb/acre). Iowa soils generally supply adequate micronutrients except on sandy soils, highly weathered soils, acid organic soils, and calcareous soils. A key exception is iron deficiency chlorosis (IDC) in soybean on calcareous soils in north-central and western Iowa; in-furrow fluid iron chelate can raise yield on these soils but not to levels seen on noncalcareous ground. Decades of Iowa State University micronutrient research (1960s-2015) across many soil types and pH ranges, testing stand-alone, foliar, and soil-applied micronutrient products, found no consistent yield response for most micronutrients. Occasional yield responses occurred with zinc in corn, and with molybdenum in soybean only on extremely acidic soils (pH ?5.4)-a condition better corrected by liming. Because of this inconsistency, most micronutrients (unlike P and K) have not been successfully calibrated to soil/tissue tests; zinc is the exception, with enough Iowa/north-central regional data to correlate soil test levels with corn and sorghum response. Recommendations: before considering micronutrients, first correct soil pH, maintain optimal P and K, and apply sulfur; then apply zinc according to soil test results for corn/sorghum. Only explore other micronutrients if budget allows, and first ask whether soil pH is optimal, soils are sandy, or deficiency symptoms are visible. For on-farm trials, include an untreated check, test multiple rates, and use both soil and tissue testing to identify which micronutrient (if any) is actually limiting, since most products showed no response beyond zinc.

Evaluation of the nutritional status of zinc and other micronutrients in maize at the critical growth stages is an important diagnostic and prognostic factor that plays a substantial role in shaping its final yield. A hypothesis was verified that the application of different phosphorus and potassium fertilization doses affected the nutritional status of zinc in maize at the critical growth stages: leaf development (BBCH 17) and flowering (BBCH 65), as well as the zinc accumulation at the stage of ripening (BBCH 89, fully ripe). A single factor field study was conducted for 5 consecutive plant growing seasons (2007-2011). The results showed that mineral fertilization significantly increased zinc concentration in maize leaves at BBCH 17 and BBCH 65 growth stages. Regardless of the effects of the experimental factor, the Zn leaf content in maize at both critical growth stages was much below the standard value. Although the zinc concentration observed at the leaf development stage was low, no significant relationship was found between the zinc nutritional status in maize at that time and the subsequent grain yield. Stronger relationships between the zinc nutritional status in maize and grain yield were observed at the flowering stage. The total accumulation of zinc in maize was significantly differentiated by the experimental factor. The chemical form of phosphorus applied had no significant effect on Zn content in maize at the critical growth stages as well as on the accumulation of this nutrient in fully ripe plants. The ZnHI value obtained in the control treatment was 51.7%, whereas the values achieved in fertilizer treatments were higher and ranged from 52.9% (W100 PAPR - with partially acidulated phosphate rock) to 57.3% (W25 - 25% of K and P recommended rate). Correlation analysis on maize yield and zinc accumulation showed that yield volumes were determined most strongly by zinc accumulation in maize vegetative organs (especially husk leaves).

Preserving crop yield is critical for US soybean production and the global economy. Crop species have been selected for increased yield for thousands of years with individual lines selected for improved performance in unique environments, constraints not experienced by model species such as Arabidopsis. This selection likely resulted in novel stress adaptations, unique to crop species. Given that iron deficiency is a perennial problem in the soybean growing regions of the USA and phosphate deficiency looms as a limitation to global agricultural production, nutrient stress studies in crop species are critically important. In this study, we directly compared whole-genome expression responses of leaves and roots to iron (Fe) and phosphate (Pi) deficiency, representing a micronutrient and macronutrient, respectively. Conducting experiments side by side, we observed soybean responds to both nutrient deficiencies within 24 h. While soybean responds largely to -Fe deficiency, it responds strongly to Pi resupply. Though the timing of the responses was different, both nutrient stress signals used the same molecular pathways. Our study is the first to demonstrate the speed and diversity of the soybean stress response to multiple nutrient deficiencies. We also designed the study to examine gene expression changes in response to multiple stress events. We identified 865 and 3375 genes that either altered their direction of expression after a second stress exposure or were only differentially expressed after a second stress event. Understanding the molecular underpinnings of these responses in crop species could have major implications for improving stress tolerance and preserving yield.

This NCERA-103 committee bulletin (NDSU Extension, revised 2025) evaluates the effectiveness of applying plant nutrients at low rates (below crop removal or below university-recommended rates), including micronutrients. Fourteen essential mineral nutrients are listed with typical concentrations in North Central Region crops (Table 1), giving reference values for B, Cu, Fe, Mn, Zn, and Mo in corn grain/stover and soybean seed/straw (e.g., corn grain: B 70 ppm, Cu 25 ppm, Fe 36 ppm, Mn 24 ppm, Zn 18 ppm, Mo 0.09 ppm; soybean seed: B 28 ppm, Cu 8 ppm, Fe 80 ppm, Mn 22 ppm, Zn 50 ppm, Mo 0.16 ppm). The document's detailed low-rate starter fertilizer research for corn and soybean focuses almost entirely on nitrogen, phosphorus, and potassium rather than micronutrients; no specific micronutrient rate trials for corn or soybean are reported in the text. Micronutrients are mentioned conceptually: crop removal of most micronutrients is small, and unlike P/K (which require ongoing fertilization due to large removal) or Ca/Mg (replaced via liming), only certain crop-nutrient combinations have consistently low soil supply requiring micronutrient fertilization-though the bulletin does not identify specific corn/soybean cases needing supplementation. For soybean specifically, the bulletin notes that foliar micronutrient fertilization (including S, Fe, B, and Zn) was tested across 18 sites in Iowa research and produced only a "similarly low positive response rate" to earlier single-nutrient foliar trials. The overall conclusion for the region is that using low rates of nutrients, including via foliar application, has not been consistently effective at increasing yield, crop quality, or profitability, and foliar micronutrient application may be best reserved for situations where soil application would be ineffective.

This conference poster evaluated the effect of integrating soybean seed inoculation with commercially available microbial inoculants and foliar boron fertilization on root system development and nodulation in the soybean cultivar Augusta. The field experiment was conducted at the University of Agriculture Experimental Station in Prusy, Poland, on high-quality wheat-complex soil. Three inoculants were compared: two bacterial products (Nitragina and Nitroflora) and one fungal (Mykoflorin). Seeds were inoculated at planting, and boron was applied twice as a foliar spray during the seedling and budding stages. Root biomass, root architecture, and root nodulation were evaluated at flowering. The combined application of bacterial inoculation and foliar boron significantly improved several root system characteristics. Treatments combining boron with Nitragina or Nitroflora produced the greatest increases in root length density, while boron combined with Mykoflorin resulted in the highest root surface area density. Although the treatments reduced mean root diameter, the combination of bacterial inoculation and boron substantially increased root nodule mass, with the highest nodule mass observed for the Nitragina plus boron treatment. Mykoflorin also increased nodulation but to a lesser extent, whereas Nitroflora was the least effective inoculant. The findings suggest that integrating microbial seed inoculation with foliar boron fertilization can enhance soybean root development and biological nitrogen fixation by improving root architecture and nodulation. This integrated management approach may help improve soybean adaptation to suboptimal growing conditions and support more sustainable production by reducing reliance on mineral nitrogen fertilizer. As this work was presented as a conference poster, the results provide preliminary evidence and do not report grain yield or long-term agronomic performance.

This research aimed to evaluate how different chemical forms of key nutrients, delivered through an advanced foliar product (PRO) and a standard formulation (TRA), influence maize performance when grown on contrasting soil types. Each fertilizer provided a set of macro- and micronutrients, including nitrogen, phosphorus, potassium, boron, copper, iron, manganese, molybdenum, and zinc, along with trace elements such as chromium, iodine, lithium, and selenium. In TRA, Fe and Zn were complexed with EDTA, and trace elements were present in mineral form. In PRO, Fe and Zn were chelated with amino acids, and trace elements were bound to plant extracts. The study examined increasing doses of PRO and their potential toxicity. Both fertilizers improved maize biomass: fresh weight increased by 5?8% and dry weight by 8?14%, depending on the dose. At the lowest dose, yields were similar. However, PRO was more effective in biofortifying maize with iron and zinc on sandy soil, increasing levels by 16% and 7% compared to TRA at the lowest dose and up to 29% at the highest dose. PRO was well tolerated at higher doses. No significant differences were observed between the second and third doses of PRO, suggesting reduced efficacy at the highest dose.

The yield forming response of maize cultivar to zinc (Zn) application depends on its timing. This hypothesis was validated in 2007, 2008, 2009 and 2010 growing seasons. The zinc treatments as the first factor were: NPK; NPK + Zn applied before sowing; NPK + Zn applied to maize at the stage of 4th leaf. The second factor was the maize type: stay-green (modern cultivars) - Paroli, Veritis, Anamur; classical (old cultivars) - Inagua, Kirola. The grain yield of modern cultivars responded the best to zinc applied before sowing, whereas the old ones, when applied to foliage. The yield of the stay-green maize depended upon the number of kernels per row, whereas the classical one on all yield structural components. The zinc management in the modern cultivars should be oriented towards maximization of the number of kernels per row, whereas in the old one on its optimization with the simultaneous kernel weight increase. The positive impact of zinc application before sowing on dry matter translocation from vegetative tissues to growing kernels underlines its practical usefulness, especially in areas with frequent water shortage during maize growth.

Maize (Zea mays L.) is one of the most widely grown cereals in the world. Its cultivation is affected by abiotic stress caused by climate change, in particular, drought. Zinc (Zn) supplied by foliar nutrition can increase plant resistance to water stress by enhancing physiological and enzymatic antioxidant defence mechanisms. One of the possibilities to reduce the effect of drought on plant production is also the utilization of trehalose. In order to confirm the effect of the foliar application of selected forms of Zn (0.1% w/v solution) - zinc oxide micro- (ZnO) and nanoparticles (ZnONP), zinc sulphate (ZnSO4) and zinc chelate (ZnEDTA) - a pot experiment in controlled conditions was conducted in combination with trehalose (1% w/v solution) on selected growth parameters of maize exposed to the drought stress. A significant effect of coapplication of Zn and trehalose on chlorophyll content, chlorophyll fluorescence parameters, root electrical capacity, weight of maize aboveground biomass (AGB) and Zn content in AGB was found. At the same time, the hypothesis of a positive effect of carbohydrates on increasing the uptake of foliar-applied Zn was confirmed, especially for the ZnEDTA and ZnSO4. This paper presents the first empirical evidence of the trehalose addition to sprays for zinc foliar fertilization of maize proving to be an effective way of increasing the resistance of maize grown under drought stress conditions.