Ontario Corn and Soybean Micronutrients Knowledge Hub

Climate change and rising carbon dioxide (CO2) levels are expected to reduce the mineral nutrient content of soybean seeds. The main objective of this study was to survey diverse soybean germplasm for variation in seed elemental concentrations and their relationships between elements, protein content, and individual seed weight. Seeds from 90 soybean genotypes were weighed and subjected to inductively coupled plasma-mass spectrometry (ICP-MS) ionomics analysis and Carbon/Nitrogen (C/N) analysis to determine protein. The results demonstrated substantial variation with the possibility of significantly improving most mineral nutrients, especially selenium (Se), copper (Cu), iron (Fe), and manganese (Mn). This diverse survey identifies genotypes that can complement existing soybean breeding programs for improving seed nutritional quality. Correlation analysis identified two clusters of co-variant elements: zinc (Zn), phosphorus (P), and sulfur (S) as well as Zn, Cu, Se, and rubidium (Rb) were positively correlated with each other. Tolerable upper limits of Rb intake are not defined for humans illustrating the need to monitor trace elements along with desirable nutrients.

This SDSU Extension article describes soybean leaf tissue analysis, including micronutrient interpretation, as a quality-control check on soil fertility and fertilizer programs. Sampling protocol: collect leaf tissue at growth stage R1-R2 (beginning to full bloom), before R3 (beginning pod), when nutrient redistribution to seed begins. Collect only the uppermost fully-developed trifoliolate leaf (commonly the third leaf from the top), excluding the petiole; gather 30 trifoliolates from different plants in the area of interest and ship in a paper bag. Lab analysis costs about $34 per sample for all 13 nutrients, or about $26 if chloride and molybdenum are excluded. Reported micronutrient sufficiency ranges (ppm), with interpretive categories of likely responsive, small probability of response, sufficiency range, and excessive/toxic: iron <50 likely responsive, 50-54 small probability, 55-300 sufficient, >500 excessive (note: requires proper leaf washing for accurate results); manganese <20 responsive, 20-29 small probability, 30-100 sufficient, >200 excessive; zinc <20 responsive, 20-24 small probability, 25-60 sufficient, >75 excessive; copper <4 responsive, 4-5 small probability, 6-20 sufficient, >50 excessive; boron <20 responsive, 20-24 small probability, 25-60 sufficient, >80 excessive; molybdenum <0.2 responsive, 0.2-0.9 small probability, 1.0-5.0 sufficient (no excessive threshold given). The article cautions that plant analysis results are most useful for adjusting future fertility programs rather than in-season correction, should be interpreted cautiously if plants were sampled under drought, flooding, or herbicide damage, and that soil testing (not tissue testing) is still required to generate actual fertilizer rate recommendations.

Modern maize (Zea mays L.) hybrids coupled with improved agronomic practices may have influenced the accumulation and partitioning of nutrient uptake since the last comprehensive studies were published. The objective of this study was to investigate nutrient uptake and partitioning among elite commercial germplasm with transgenic insect protection grown under modern management practices. Plants were sampled at six growth stages and divided into four fractions for nutrient determination. Total nutrients required per hectare to produce 23.0 Mg ha(-1) of total biomass with 12.0 Mg ha(-1) of grain included 286 kg N, 114 kg P2O5, 202 kg K2O, 59 kg Mg, 26 kg S, 1.4 kg Fe, 0.5 kg Mn, 0.5 kg Zn, 0.1 kg Cu, and 0.08 kg B. A 10-d period (V10-V14) denoted the maximum rates of accumulation on a per day basis for dry weight (439 kg), N (8.9 kg), P2O5 (2.4 kg), K2O (5.8 kg), Mg (2.2 kg), S (0.7 kg), Zn (14.2 g), Mn (18.0 g), B (3.3 g), Fe (95.3 g), and Cu (3.0 g). The majority of total uptake occurred post-flowering for P, S, Zn, and Cu. Harvest index values of P (79%), S (57%), Zn (62%), and N (58%) were identified in the grain. These results provide much needed data on the nutrient uptake and partitioning of current hybrids, and provide an opportunity to further refine fertilizer method and timing recommendations for maize biomass and grain production.

Highlights: • Nutrient seed priming improves early seedling development and root growth of maize exposed to low root zone temperatures. • Low soil or root zone temperature (RZT) is a major problem for maize growth in Central and Northern Europe. • In maize, low RZT severely inhibits the early seedling establishment, root growth and nutrient uptake. • Micronutrient seed priming significantly improved early seedling development and nutrient uptake under low RZT. • Although nutrient priming increased grain yield but the mechanisms behind require further research.

The absence of recent data regarding the nutritional needs of modern soybean [Glycine max (L.) Merr.] production systems necessitates a greater comprehensive understanding of nutrient uptake, partitioning, and remobilization. The objective of this study was to evaluate macro- and micronutrient accumulation and partitioning in current soybean cultivars. Across 3 site-years, plants were sampled at seven growth stages and divided into four plant tissue fractions for quantification of nutrient uptake. Accumulation (per ha) of 275 kg N, 21 kg P (48 kg P2O5), 172 kg K (207 kg K2O), 113 kg Ca, 50 kg Mg, 19 kg S, 335 g Zn, 371 g Mn, 325 g B, 849 g Fe, and 63 g Cu were required to produce approximately 3500 and 9500 kg ha-1 of grain and total biomass, respectively. Supplemental fertility modestly increased biomass and yield (2%), but did not alter nutrient partitioning or harvest index. Nutrients with high harvest index (i.e., percentage of total nutrient accumulation partitioned to grain) values included P (81%), N (73%), Cu (62%), and S (61%), which may serve as a limitation to high yield. Seasonal patterns of nutrient accumulation suggested that K and Fe were acquired primarily during late vegetative growth while the uptake of N, P, Ca, Mg, S, Zn, Mn, B, and Cu were more equally distributed between vegetative and seed-filling growth phases. These results document the rate and duration of macro- and micronutrient accumulation in soybean, and highlight the importance of adequate nutrient availability during key crop growth periods.

Understanding the interaction of macro- and micronutrients is a prerequisite to targeting nutrient balance in crop production. A 3-year field study was conducted to determine mineral nutrient uptake of maize hybrids with N fertilizer application under different rotation systems. The experiment was arranged in a split-plot design with rotation [maize-alfalfa (MA), maize-soybean (MS), and continuous maize (MM)] by N rate (0, 50, 100 and 150 kg N ha(-1)) as the mainplot and hybrid as the subplot. Two additional treatments (200 and 250 kg N ha(-1)) were tested in MM. Maize plant total Mg, Zn, and Cu content were in the order: MA MS MM. Plant Fe uptake was the lowest in MA and not affected by N input. The increased Cu uptake with increasing N rates indicated the synergism of these two nutrients, whereas dilution effects of N application on stover Zn and Mg concentrations were recorded. Rotation systems and N rates interactively affected nutrient harvest index and internal efficiency of Zn, Mg, Fe, and Cu. Relationships of plant N with Cu and Mg concentrations, and N with Zn, Mg, and Cu content at the V6 stage were established, but they were not necessarily preserved at maturity due to the progressive synergistic and dilution effects. The findings of nutrient uptake of Cu, Zn, Mg and Fe and their relationships with N nutrition in maize with stacked transgenic traits are important for developing best management practices to achieve concurrent improvements in nutrient use efficiency and crop productivity.

Methods: Iowa State University researchers (Mallarino et al., 2011 ICM Conference) measured micronutrient (boron, manganese, zinc) concentrations in corn and soybean grain across long-term Iowa research-farm trials (multiple counties, no-till and chisel-plow/disk tillage, several P/K fertilizer treatments, spanning years/sites) as part of a broader P/K removal and residue-recycling study. Grain samples were analyzed for nutrient concentration, and micronutrient removal was calculated from concentration × yield across a wide range of corn and soybean grain yields. Findings: Micronutrient uptake by both crops is very small, typically under 1% of P or K uptake, so grain concentrations and removal amounts are correspondingly minor. Across all fields, years, and treatments, there was no relationship between grain yield level and B, Mn, or Zn concentration in either crop, though boron showed unusually wide variation among high-yielding corn fields (removal ranging from near zero to about 0.08 lb/acre). In corn, removal of B, Mn, and Zn increased with yield in a slight exponential pattern (steeper increase at higher yields) rather than the linear pattern seen for P and K. In soybean, micronutrient concentrations in grain were several times higher than in corn, but removal-yield relationships were linear (not exponential) and more variable than in corn; zinc removal by soybean was roughly double that of corn, while boron and manganese removal were only slightly higher than corn. The authors concluded that because removed amounts are insignificant relative to soil reserves and to P/K removal, micronutrient removal should not be used as a fertilization-decision criterion the way it is for P and K, and flagged a need for further research on how removal affects soil/tissue micronutrient levels and fertilizer requirements over time.

This industry blog post (OMEX Canada) promotes calcium (Ca) and molybdenum (Mo) seed dressings for soybean, framing both as micronutrients important for early nodulation. It states these seed treatments are not supported by traditional extension research or recommended by agronomic associations, and notes North Dakota State University found no consistent or significant yield response to such dressings. According to OMEX's CEO (a former University of Manitoba plant pathologist), calcium acts as a signal that allows compatible rhizobia bacteria to enter soybean roots and initiate nodule formation, while molybdenum is a cofactor for nitrate reductase, the enzyme needed for nitrogen metabolism and nodule function; without adequate Mo, nodulation is poor and nodules are non-functional. Symptoms attributed to molybdenum deficiency include poor leaf structure and weak, pale leaf color, since nitrate reductase reportedly makes up a large share of leaf structure. Soil Mo in the region is described as generally adequate, but repeated canola crops can deplete supply. Molybdenum is stated to be mobile in phloem and xylem, so foliar correction after emergence is possible; calcium/molybdenum seed dressings are presented as a first line of defense at planting. The company's spokesperson claims seed dressings can produce four to five-bushel yield gains in stress years, though this is an industry/marketing source rather than peer-reviewed research, and the article itself acknowledges the scientific basis remains debated with regulatory changes only recently easing product availability in Canada.

This North Central Extension-Industry Soil Fertility Conference (2015) bulletin by Mallarino, Camberato, Kaiser, Laboski, Ruiz-Diaz, and Vyn synthesizes multi-state micronutrient trials for corn and soybean. Overall: micronutrient deficiencies are not widespread in the north-central region and mostly occur on sandy, calcareous, or high-pH soils. Indiana: soybean Mn response was inconsistent; one 2007 trial on a Mn-deficient soil (Mehlich-3 Mn 12 ppm) showed a 6 bu/acre yield increase from foliar or banded Mn combined with starter N-P, but Mn alone gave no benefit, and results varied 5-15% and by location/year. Iowa: 2012-2014 trials across 30+ soil series (46 soybean, 11 corn fields) testing foliar/soil B, Cu, Mn, Zn found no statistically significant yield response at any conventional-plot trial; existing soil/tissue sufficiency interpretations over-predicted deficiency response. Kansas: seed-applied chelated ortho-ortho EDDHA-Fe increased soybean yield ~55% on severe iron deficiency chlorosis (IDC) soils (pH 8.1-8.5), but foliar Fe had no effect; separate trials found no yield benefit from starter/foliar B, Cu, Mn, Zn blends in corn or soybean without a deficiency history, except one sandy site with a 6 bu/acre gain from broadcast micronutrient mix. Minnesota: Fe (as o-o-EDDHA "Soygreen," 3 lb/acre on seed) increased soybean yield 3-4 bu/acre in IDC-prone areas; other micronutrients (Zn, Mn, Mo, B) showed no consistent yield benefit across 12 site-years, and 2 lb B/acre broadcast occasionally reduced yield. Wisconsin: three years of starter/foliar Mn trials (0-5 lb Mn/acre starter; 1.25 lb Mn/acre foliar at R1/R3) found tissue Mn below sufficiency ranges (54-300 ppm) at all sites, yet no consistent yield response, suggesting the sufficiency range may be too high. Overall conclusion: soils in the region generally supply adequate micronutrients for corn/soybean; Fe management for IDC is the clearest exception with proven response; decisions on other micronutrients should target only sandy, calcareous, organic, or severely eroded fields rather than broad application.

This multi-state (IA, MN, KS, WI, IN/PU) Extension bulletin reviews soybean micronutrient management. Micronutrient deficiencies in the region are uncommon except for iron (Fe) and manganese (Mn); soil/tissue test interpretations are poorly calibrated due to infrequent responses. Boron (B): deficiency rare, no documented regional yield increases from B fertilization, and soybean is very sensitive to B toxicity (yield decreases reported in MN); avoid in-furrow/seed placement. Copper (Cu): soybean among least Cu-sensitive crops; 42 Iowa and 10 Kansas trials found no yield increase, one Iowa site showed a yield decrease from Cu application. Chlorine (Cl): deficiencies rare; IA, MN (20 lb Cl/acre), and KS (5-20 lb Cl/acre) trials found no soybean yield response (IA trial did boost corn yield). Iron: causes IDC, a major yield-limiting issue in the western Corn Belt tied to high pH/carbonate soils; broadcast Fe and DTPA/EDTA chelates gave inconsistent results, but seed/in-furrow ortho-ortho-EDDHA chelate consistently reduced IDC and increased yield; IDC-tolerant varieties and oat companion crops (reducing soil nitrate) also help. Manganese: deficiency tied to calcareous/organic soils, common in parts of IN, MI, OH, WI; foliar or planter-banded Mn (0.2-0.5 lb/acre chelate or 1-1.25 lb/acre sulfate) is most effective since broadcast Mn becomes unavailable; banded-plus-foliar combinations maximize response; recent large-scale IA/KS/MN trials (99+ sites) found essentially no yield response even where soil tests predicted deficiency, though one sandy-soil site responded to Mn. Foliar Mn can antagonize glyphosate. Molybdenum: linked to N fixation; deficiency corrected via liming rather than direct Mo fertilization. Zinc: soybean much less Zn-sensitive than corn; regional trials found no yield increase from Zn even on soils where corn would respond. Overall message: confirmed micronutrient responses in soybean are rare regionally, and current soil/tissue test thresholds often over-predict deficiency.