Ontario Corn and Soybean Micronutrients Knowledge Hub

Slurry injection below the maize (Zea mays L.) row may substitute a mineral nitrogen (N) phosphorus (P) starter fertilizer (MSF) and thus reduce nutrient surpluses in regions with intensive livestock husbandry. We investigated the plant P, zinc (Zn), and manganese (Mn) status compared to the current farm practice. In 2014 and 2015 field trials were conducted to evaluate plant nutrient status at different growth stages. Besides an unfertilized control, two slurry injection treatments (±nitrification inhibitor (NI)) were compared to slurry broadcast application plus MSF. In both experiments NI addition significantly increased nutrient concentrations during early growth (6-leaf 2015: +33% P, +25% Zn, +39% Mn). Under P deficiency due to cold weather conditions broadcast application showed higher P uptake until 6-leaf (36-58%), while it was lower at 8-(32%) and 10-leaf (19%) stage compared to slurry injection (+NI). Zn availability was enhanced for slurry injection (+NI) during early growth and Zn and Mn uptakes were higher at harvest. Slurry injection decreased P balances by 10-14 kg P ha-1, while Zn and Mn balances were excessive independent of treatments. Slurry injection (+NI) can substitute a MSF without affecting early growth and enhances the Zn and Mn status. This new fertilizing strategy enables farmers to reduce P surpluses.

Maize is becoming an increasingly important crop in northern Europe, but low temperatures during spring may hamper its growth. This effect may be caused by direct plant damage through oxidative stress or indirect damage through decreased uptake of nutrients, especially phosphorus (P), from the soil. Previous studies have indicated that treatment with micronutrients such as manganese and zinc (Mn/Zn), microbial inoculants (biostimulants) or exogenous salicylic acid can alleviate abiotic stress. Seed inoculation with microorganisms can also increase P uptake from the soil. In a pot experiment, we investigated whether the negative effects of cold stress could be alleviated by improving soil fertility (P level), inoculating seed with two different plant growth-promoting fungi of the genus Penicillium sp., adding extra Mn/Zn at sowing or adding exogenous salicylic acid. These treatments were tested on maize plants subjected to cold stress and two different levels of soil fertility and harvested 28 and 51 days after sowing (DAS). We found that the effect of cold stress was not alleviated by improving soil fertility through the use of a more fertile (high P) soil or through fertilisation with plant-available P in the form of triple superphosphate. Cold stress was also not alleviated by the treatment of seeds with salicylic acid. Addition of Mn/Zn and inoculation with one of the two Penicillium strains tested increased biomass production at 51 DAS (compared with the untreated control) in cold-stressed plants grown in the high P soil, but not in the low P soil. Thus, addition of Mn/Zn and inoculation with Penicillium sp. can reduce the effects of cold stress in maize plants grown in fertile soil.

Manganese deficiency in soybean [Glycine max (L.) Merr.] reduces seed yield and alters the oil profile. The objective of this study was to evaluate the effect of foliar Mn fertilizer on seed yield, protein and oil concentration, and the oil profile of transgenic high-oleic soybean ('Plenish') and soybean with a normal oil profile (referred to here as conventional"). Research trials were established in 2014 and 2015 at two locations in Ohio. Treatments included soybean cultivar (four to six Plenish cultivars and two conventional cultivars) and foliar Mn fertilizer application at the R3 soybean growth stage (none, MnSO4, and Mn--EDTA). In 2014, the Mn--SO4 application increased soybean seed yield by 140 kg ha-1 at the Wood County location where soybean plants were deficient in Mn. Although Mn-SO4 also supplies S, no S deficiencies were detected. At the other three site-years, soybean seed yield was not affected by Mn application. Manganese application did not influence the oil or protein content of the soybean seed or alter the oil profile. The high-oleic cultivars produced similar yield to the conventional cultivars at the Wood County location both years. In 2014 and 2015 at the Clark County location, the high-oleic cultivars yielded 410 and 270 kg ha-1 less than cultivars with a conventional oil profile, respectively. Plenish soybean cultivars did not need to be managed differently from the conventional soybean cultivars tested in terms of Mn foliar application."

Reduced atmospheric S deposition, in conjunction with higher grain sale prices and steadily increasing yields of soybean [Glycine max (L.) Merr.], has many growers considering an increase in secondary and micronutrient applications. Limited information exists quantifying requirements of S, Mg, Ca, Zn, Mn, Cu, Fe, and B across a wide yield range for modern soybean production systems. Using six site-years and eight varieties, plants were sampled at six growth stages and partitioned into their respective plant parts and analyzed. Nutrients were acquired heavily (48-73%) from R1 through R5.5 with peak uptake rates near R3. Yet, uptake after R5.5 represented a greater portion of total S uptake as yield increased from the low (24.9%) to high (32.2%) yield level (3608 vs. 5483 kg ha-1). This coincided with seed S accumulation, which relied more heavily on continued uptake after R5.5 (58%) vs. vegetative S remobilization (42%). Across all environments (site × year) and varieties, total S uptake (0.004 kg S kg grain-1) and removal (0.003 kg S kg grain-1) showed moderate (R2=0.58) and strong (R2=0.76) relations with yield, respectively. These relations for each micronutrient were much weaker (R2=0.13-0.66), due largely to the main effects of environment and variety along with their respective interactions with yield. Furthermore, micronutrient concentrations in leaf tissue varied considerably (CV=28-46%) during recommend testing stages. Thus, previously reported inconsistent yield responses to foliar application of these micronutrients may primarily be due to the large variability in leaf tissue concentrations and nutrient requirements.

This Iowa State Extension presentation (J.E. Sawyer) reviews micronutrient issues for corn and soybean, focused on zinc (Zn) and iron (Fe), plus context on sulfur research methodology. For corn, Zn deficiency risk factors are low organic matter, high pH (>7.4), eroded/coarse-textured soils, high P with borderline Zn, and cool/wet soils. ISU Zn recommendations for corn (DTPA-extractable Zn): Low (0-0.4 ppm) = 10 lb Zn/acre broadcast or 2 lb/acre banded; Marginal (0.5-0.8 ppm) = 5 lb broadcast or 1 lb banded; Adequate (0.9+ ppm) = none. However, prior ISU trials (Webb 1970s-90s; Bickel & Killorn 2007) found inconsistent yield responses to Zn even at low soil-test levels. For soybean, iron deficiency chlorosis (IDC) is linked to high pH (>7.4), free calcium carbonates, high salts, poor aeration, high soil nitrate, and wet conditions. Management: choose IDC-tolerant varieties; soil-applied Fe, sulfur, or gypsum are not effective; seed-coated iron is expensive with limited response; in-furrow chelated FeEDDHA may help; reducing soil nitrate (e.g., interseeding soybean into a cover crop) may help. Foliar FeEDDHA (Sequestrene 138) can be applied at the two-trifoliate stage, within 7 days of chlorosis symptoms, at 0.15 lb Fe plus surfactant in 15-30 gal water/acre, possibly requiring multiple applications. A 2012-2014 ISU research program (46 soybean trials, 10 corn trials; foliar B/Cu/Mn/Zn; 26 additional strip trials; 8 soil-applied trials) found very unlikely yield response to micronutrients in Iowa: no yield increase in foliar plot trials (one soybean decrease from Cu/Zn/mixture), mixed results in strip trials (one soybean increase, one corn decrease), and no effect from soil application. Conclusions: published soil/tissue sufficiency levels are likely too high, soil and tissue tests show little agreement, and yield level is a poor predictor of micronutrient need. Overall recommendation: don't rely heavily on published test interpretations (use lowest suggested sufficiency values), lime acid soils, and watch sandy, eroded, or calcareous fields for Zn/Fe issues.

A 2-year crop rotation study in southern Manitoba assessed the effects of starter fertilizer on grain corn (Zea mays L.) production when corn followed canola (Brassica napus L.) versus soybean (Glycine max L. Merr.). Treatments included a control (no starter) and two rates of phosphorus (P) (30 and 60 kg P2O5 ha-1) as monoammonium phosphate (MAP, 11-52-0) or MicroEssentials® SZ (MESZn, 12-40-0-10-1) side-banded at planting. The preceding crop did not have any influence on mycorrhizal colonization of corn roots at the V4 corn growth stage. However, side-banded fertilizer increased early-season biomass by as much as 111% compared to the unfertilized control, averaged across all site-years, with the largest increases occurring where corn followed canola. P concentration and uptake in early-season biomass increased as the P rate increased. Zinc (Zn) concentrations in early-season biomass were the greatest for the unfertilized control and MESZn treatments, while Zn uptake was significantly greater with the application of starter fertilizer compared to the unfertilized control. Starter P advanced silking date by 2-7 days relative to the unfertilized control. At maturity, starter P reduced grain moisture by 21-27 g kg-1 in corn only after canola. The high rate of MAP increased grain yield by an average of 770 kg ha-1 compared to the unfertilized control, regardless of the preceding crop. The negative influence of the preceding canola crop on early-season growth and mid-season development of corn can be managed with starter fertilization to provide adequate P and Zn to the corn crop and maintain successful production in Manitoba.

Soybean yields can be considerably improved by inoculation with selected Bradyrhizobium japonicum strains and foliar fertilization. An exact field experiment was carried out in 2012-2014 at the Experimental Station of Cultivar Assessment in Przeclaw, Poland. The test plant was soybean cv. Aldana. The experimental factors were: bacterial inoculant Nitragina (Bradyrhizobium japonicum); foliar fertilization with Mikrokomplex; combined applications Nitragina + Mikrokomplex and the control treatment. Significant effect of Nitragina on an increase in the number of plants prior to harvest, plant height and the number of pods per plant was indicated. Fertilization with Mikrokomplex caused an increase in the number of pods per plant and thousand seed weight. Nitragina + Mikrokomplex increased the number of plants prior to harvest, plant height, the number of pods per plant and thousand seed weight. Seed yield was significantly higher in all the treatments compared to the control (2.31 t/ha). Higher soil plant analysis development values were found after the application of Nitragina + Mikrokomplex, and in the stage of pod development, also after foliar fertilization with Mikrokomplex. Application of Nitragina and Nitragina + Mikrokomplex resulted in an increase in leaf area index and mean tip angle and total protein in seeds. Fe content in seeds was the lowest in the control (69.2 mg/kg) and significantly higher in the other treatments (Nitragina, Nitragina + Mikrokomplex), and Mg content significantly increased after the application of Mikrokomplex and Nitragina + Mikrokomplex.

Historically, corn (Zea mays L.) ear-leaf N concentrations at mid-silking have been positively correlated with grain yield (GY). Many state and regional fertilizer recommendations provide nutrient sufficiency ranges" or threshold nutrient concentrations for N and other nutrients in ear leaves sampled at silk emergence, but these are based on studies conducted decades ago with much lower yielding hybrids grown at lower plant densities. In response to this potential knowledge gap, we collected corn ear-leaf samples at mid-silking in field studies conducted near West Lafayette, IN, from 2010 to 2016. These field studies involved comparisons of multiple hybrids, plant densities or tillage systems for their response to nutrient management alternatives (e.g., macronutrient rates, placement, and timing). The ear-leaf samples were analyzed for nutrient concentrations (N, P, K, Ca, Mg, S, Zn, Mn, Fe, Cu, B, and Al), and each plot's nutrient concentration data were subjected to regression analysis to evaluate their relationship with plot level dry matter (DM) accumulation and GY responses. Variation in ear-leaf N, P, S, and Cu concentrations explained 50%, while Fe explained 40%, of the variation in both GY and DM. These nutrients (N, P, S, Cu, and Fe) were also positively correlated with each other (Pearson r ranged from 0.46-0.89). However, ratios of ear-leaf nutrient concentrations at silking consistently explained less of the GY variation than single nutrient concentrations. The overall relationships of ear-leaf nutrient concentrations with GY suggests revisions in state recommendations for ear-leaf "nutrient sufficiency" may be warranted for some nutrients."

In soybean [ Glycine max ( L.) Merr.], iron deficiency results in interveinal chlorosis and decreased photosynthetic capacity, leading to stunting and yield loss. In this study, gene expression analyses investigated the role of soybean replication protein A ( RPA) subunits during iron stress. Nine RPA homologs were significantly differentially expressed in response to iron stress in the near isogenic lines ( NILs) Clark (iron efficient) and Isoclark (iron inefficient). RPA homologs exhibited opposing expression patterns in the two NILs, with RPA expression significantly repressed during iron deficiency in Clark but induced in Isoclark. We used virus induced gene silencing ( VIGS) to repress GmRPA3 expression in the iron inefficient line Isoclark and mirror expression in Clark. GmRPA3-silenced plants had improved IDC symptoms and chlorophyll content under iron deficient conditions and also displayed stunted growth regardless of iron availability. RNA- Seq comparing gene expression between GmRPA3-silenced and empty vector plants revealed massive transcriptional reprogramming with differential expression of genes associated with defense, immunity, aging, death, protein modification, protein synthesis, photosynthesis and iron uptake and transport genes. Our findings suggest the iron efficient genotype Clark is able to induce energy controlling pathways, possibly regulated by SnRK1/ TOR, to promote nutrient recycling and stress responses in iron deficient conditions.

The most efficient way of soybean (Glycine max (L.) Merrill) iron deficiency chlorosis (IDC) management is to select a tolerant cultivar suitable for the specific growing condition. These cultivars are selected by field experts based on IDC visual ratings. However, this visual rating method is laborious, expensive, time-consuming, subjective, and impractical on larger scales. Therefore, a modern digital image-based method using tree-based machine learning classifier models for rating soybean IDC at plot-scale was developed. Data were collected from soybean IDC cultivar trial plots. Images were processed with MATLAB and corrected for light intensity by using a standard color board in the image. The three machine learning models used in this study were decision tree (DT), random forest (RF), and adaptive boosting (AdaBoost). Calculated indices from images, such as dark green color index (DGCI), canopy size, and pixel counts into DGCI ranges and IDC visual scoring were used as input and target variables to train these models. Metrics such as precision, recall, and f1-score were used to assess the performance of the classifier models. Among all three models, AdaBoost had the best performance (average f1-score = 0.75) followed by RF and DT the least. Therefore, a ready-to-use methodology of image processing with AdaBoost model for soybean IDC rating was recommended. The developed method can be easily adapted to smartphone applications or scaled-up using images from aerial platforms.