Ontario Corn and Soybean Micronutrients Knowledge Hub

The action-to-reaction dynamics of next-generation nanofertilizers (NFs) towards field crops are currently being addressed in precision and sustainable agriculture. Therefore, our aim was to evaluate the effects of foliar application of ZnO nanoparticles (ZnO-NPs) or their combination with hybrid nanoporous biosilica mixed with yeast (ZnSi-bio) for soybean plants' selected production and physiological indices in comparison to an NF-free control. The experiment was conducted at eco-friendly concentrations in Veľký Krtí?, Slovakia, a location within the Central European agronomical region. The ZnSi-bio variant had an improved number of pods, seed count, and yield, while the ZnO-NPs variant had an enhanced seed bulk density compared to the NF-free control, which had a greater effect on thousand-seed weight (TSW). Significant differences were found in the final quality components of soybeans with respect to phosphorus content without ZnO-NP biofortification. In the case of the ZnSi-bio variant, soybeans were biofortified with zinc. Both leaf-applied NFs markedly improved nutritional and energetic values for soybeans. NFs continued to positively affect seasonal physiology, such as the stomatal conductance (Ig) and crop water stress index (CWSI), compared to the control. The results suggest that the ZnO-NPs, especially when combined with hybrid biosilica and yeast, open new avenues for interdisciplinary research in agro-food science.

Illinois ranks second in soybean [Glycine max (L.) Merr.] production in the United States with an annual crop value of some $4 billion. To discover what management practices, soil parameters, and environmental conditions enable higher soybean yields, the Illinois Soybean Association (ISA) started in 2010 a state-wide Yield Challenge" (YC) program. Enrolled producers established a "challenge" plot and adjoining "standard" practices plot, and agreed to share crop management information, soil samples, and yield data. Our work describes data analyses and findings using data generated under this program. Yields differed between standard and challenge plots across the state, with foliar applications of fungicide and or insecticide resulting in significant yield increases. Using principal component analyses and multiple regression tools, we were able to explain about 54% of the variation in soybean yield for the state in 2010. Within the available data range, delays in planting date and increased row spacing both reduced soybean yields, and tilled fields yielded more than no-tilled soybean fields. We uncovered a negative trend between soybean yield and PC1, formed by soil cation exchange capacity (CEC), dominant cations, and soil organic matter (SOM), likely due to the drainage characteristics of the plots. Yields were also decreased with increasing values of PC3, a variable that includes soil pH, Mn levels, and soybean cyst nematode (SCN) egg count. On the other hand, higher soil test values of P, Zn, Fe, and K, included in PC2, were related to higher soybean yields. We see this as a promising start to identifying management factors that may be addressed as we continue the search for higher soybean yields."

This South Dakota State University Extension chapter (iGrow Corn Best Management Practices, revised 2023) provides fertilizer recommendation guidance for corn, including a specific section on zinc (Zn) and iron (Fe). Micronutrient deficiencies generally result from environmental conditions and can be temporary; soil testing is recommended when deficiency is suspected. In most cases, secondary nutrients (Ca, Mg, S) and micronutrients (B, Zn, Fe, Cu, Mo, Mn) have limited impact on South Dakota corn yields. Zinc deficiency can occur on coarse-textured soils, eroded soils, organic soils, or soils with high phosphorus levels; cool, wet soil conditions can worsen Zn availability, causing feathering/striping symptoms on the youngest leaves. Zinc recommendations (Table 23.8, based on zinc sulfate) by DTPA soil test level: 0-0.25 ppm (very low) and 0.26-0.50 ppm (low) = 10 lb Zn/acre; 0.51-0.75 ppm (medium) = 5 lb/acre; 0.76-1.00 ppm (high) = 2.5 lb/acre; >1.00 ppm (very high) = 0 lb/acre. As of 2015 these rates were under revision, with initial analysis suggesting 2.5 lb Zn/acre for the high range. Iron deficiency may occur on leveled or eroded soils where calcareous subsoil is exposed, producing yellowing with interveinal striping on younger leaves. Fe recommendations by soil test ppm: 0-2.5 (low) and 2.6-4.5 = 0.15 lb Fe/acre; >4.5 ppm = 0 lb/acre. Correcting Fe deficiency is difficult; applying manure or biosolids is suggested as an effective approach to minimize yield loss from Fe chlorosis.

Chelates such as ethylenediaminetetraacetic acid (EDTA) enter the environment from various sources but its impact on crop growth and mineral uptake has been evaluated only sporadically. In a pot experiment with graded EDTA applications the impact of free EDTA on crop performance, macro- and microelement uptake was assessed. The sensitivity towards EDTA decreased from sunflower oilseed rape maize. Maize was the least sensitive crop showing no visual toxicity symptoms, however, a reduction in biomass development. In comparison, oilseed rape and sunflower displayed necrotic lesions on their leaves and biomass development was significantly reduced when higher rates of EDTA were applied. Soil EDTA application increased the uptake of Mn and Zn in shoots of all three crops and in roots of maize and sunflower. In maize EDTA increased not only the uptake of Mn and Zn, but also all other investigated micronutrients in shoots with the only exception of copper. In oilseed rape EDTA applications increased the uptake of Cu, Mn and Zn in shoots while the Fe, Mn and Mo content decreased in roots. Changes in the micronutrient content in shoots of sunflowers were similar to that in oilseed rape. In roots EDTA increased the Mn uptake. Next to micronutrients EDTA influenced the macronutrient uptake of the tested crop plants.

Selection of a resistant cultivar is the most practical control measure for iron deficiency chlorosis in soybean (Glycine max L. Merr.). Plant breeders routinely evaluate cultivars for chlorosis resistance in hill plots, but this procedure may overestimate the chlorosis resistance of a cultivar. The objective of this research was to compare the chlorosis scores of soybean cultivars differing in chlorosis resistance, planted in conventional 76-cm rows, or with two, four, or eight plants per hill. In both 2001 and 2002, it was estimated that three plants per hill would give average chlorosis scores most similar to that observed in 76-cm rows. The highest overall precision was given with row plots, and the lowest with two plants per hill. Hill plots are more space-efficient than row plantings, but are much more easily lost due to animal predation.

Iron deficiency chlorosis (IDC) is a global crop production problem, significantly impacting yield. However, most IDC studies have focused on model species, not agronomically important crops. Soybean is the second largest crop grown in the United States, yet the calcareous soils across most of the upper U.S. Midwest limit soybean growth and profitability. To understand early soybean iron stress responses, we conducted whole genome expression analyses (RNA-sequencing) of leaf and root tissue from the iron efficient soybean (Glycine max) cultivar Clark, at 30, 60 and 120 min after transfer to iron stress conditions. We identified over 10,000 differentially expressed genes (DEGs), with the number of DEGs increasing over time in leaves, but decreasing over time in roots. To investigate these responses, we clustered our expression data across time to identify suites of genes, their biological functions, and the transcription factors (TFs) that regulate their expression. These analyses reveal the hallmarks of the soybean iron stress response (iron uptake and homeostasis, defense, and DNA replication and methylation) can be detected within 30 min. Furthermore, they suggest root to shoot signaling initiates early iron stress responses representing a novel paradigm for crop stress adaptations.

Soybean (Glycine max L.) is a new cash crop grown in north central and northwestern North Dakota (ND). Soils and climate in these new soybean areas differ from current fertilizer guidelines. A three-year study to evaluate soybean fertility best management practices was initiated in the spring of 2016 and concluded in 2018. Each year had two sites and twelve treatments. One site was acidic (pH 6.2) and the other was alkaline (pH 7.2). Both site treatments were: untreated check, inoculated with rhizobia (Bradyrhizobium japonicum L.), broadcast urea (55 kg ha-1), broadcast MAP (110 kg ha-1), In-furrow 10-34-0 (28 L ha-1), in-furrow 6-24-6 (28 L ha-1), foliar 3-18-18 (28 L ha-1) at V5 and R2, and foliar 3-18-18 (28 L ha-1) with sulfate (1.1 kg ha-1) at V5 and R2. The acidic site had two treatments of sugar beet (Beta vulgaris L.) waste lime (4411 kg ha-1 and 8821 kg ha-1). The alkaline site received treatments of iron ortho-ortho-EDDHA (7.1 L ha-1), and naked ortho-ortho-EDDHA (7.1 L ha-1). An in-furrow treatment of cobalt (2.9 kg cobalt-sulfate ha-1) was added in 2018. Fertilizer treatments did not impact soybean yield, protein content and oil content at the 0.05 significance level.

This University of Minnesota Extension guide, "Fertilizing Corn in Minnesota" (revised 2025), devotes its "Micronutrient needs" section to corn. Overall, corn takes up less than one pound of micronutrients per acre, and while micronutrients are needed for optimal growth, they may not need fertilizer application. Zinc (Zn) is identified as the only micronutrient likely needed in a Minnesota corn fertility program, and corn is the only agronomic crop that consistently responds to Zn fertilization. The DTPA soil Zn test reliably predicts need. Recommended rates by DTPA soil Zn test level: 0.0-0.25 and 0.26-0.50 ppm = 2 lb/acre banded or 10 lb/acre broadcast; 0.51-0.75 ppm = 1 lb/acre banded or 5 lb/acre broadcast; ?0.76 ppm = 0 lb/acre (no response expected). Banded Zn is generally preferred for immediate response, though broadcast provides better carryover to future years. Most Zn sources are equally effective except large zinc oxide particles; chelated Zn (especially EDTA-chelated) offers the most stable availability across soil pH and is often used in liquid starter fertilizers, though it costs more per lb of Zn and does not improve response on soils already testing ?0.75 ppm. Boron (B) is unlikely to increase corn yield across Minnesota soils; only a small chance of response exists on sandy soils with <1.0% organic matter and B soil test ?0.08 ppm. If deficiency is suspected, trial applications should not exceed 1-2 lb B/acre broadcast, and there are no guidelines for foliar B due to toxicity risk at low rates. Iron (Fe), copper (Cu), and manganese (Mn) fertilization is not recommended for Minnesota corn under current guidelines, as these micronutrients are not considered yield-limiting in the state's corn production systems.

This University of Minnesota Extension bulletin (AG-FO-03813-D, revised 2020) covers soybean fertility, with micronutrient guidance concentrated in two sections. Iron Deficiency Chlorosis (IDC): occurs on soils with pH ? 7.4 (no true soil Fe shortage; uptake is blocked). No easy fix, but severity can be reduced by: 1) selecting tolerant varieties (chlorosis scores published by UMN and seed companies); 2) minimizing plant stress (avoid certain post-emergence herbicides, high-salt soils, deep cultivation, soil compaction, seedling disease, and carryover soil nitrate, which worsens IDC); 3) seed-applied EDDHA-Fe chelate (ortho-ortho form) at 1-3 lb active ingredient/acre, shown to increase yield; and 4) an oat companion crop seeded at 1.5 bu/acre and killed at 10-inch height, which reduces IDC in severely affected areas. Recommended practice for IDC-prone fields: plant a tolerant variety plus in-furrow EDDHA-Fe and/or an oat companion crop. Other micronutrients: Minnesota trials found no soybean yield response to magnesium, zinc, or copper, so these are not recommended despite reported links between glyphosate-tolerant soybean and possible manganese/micronutrient deficiencies. Boron: soybean has low tolerance to B; broadcast rates as low as 2 lb B/acre can cause toxicity, and research shows no yield benefit from B application, with high rates more likely to reduce yield. Manganese: no widespread Mn need demonstrated in Minnesota, but soybean may respond on soils with pH > 7.4 and DTPA soil Mn (0-6") ? 10 ppm; in these cases, 10 lb Mn broadcast/acre may be warranted. Foliar Mn has not been tested in Minnesota and should only be tried experimentally. On more acidic soils with low DTPA Mn, no consistent Mn benefit was found. Overall guidance: prioritize Fe management for IDC-prone fields; skip Mg/Zn/Cu/B fertilization; consider Mn only on high-pH, low-Mn-test soils.

Soybean [Glycine max (L.) Merr.] production is significantly reduced by iron (Fe) deficiency chlorosis under calcareous soils of the Northern Great Plains. On-farm trials were conducted to evaluate the foliar applications of Fe fertilizer forms and addition of different adjuvants according to regreening of leaves and yield. Treated plots had improved visual chlorosis ratings and chlorophyll soil plant analysis development (SPAD) meter readings over the growing season than control, but differences were not significant (P0.05). Foliar application of Fe-EDDHA had the most consistent increase in yield over control of the Fe chelates, but no single adjuvant performed better than the others. Future research should focus on integrating other practices like cultivar selection and high seeding rate with foliar application to control Fe deficiency chlorosis.