Zinc biofortification in wheat grains through phosphorus and zinc fertilization strategies in Manitoba’s Red River Valley

Abstract

Canada is one of the world’s largest wheat exporters, yet zinc (Zn) concentrations in Canadian wheat often fall below levels considered optimal for human health. We evaluated agronomic biofortification options that align with Canadian prairie practices by testing phosphorus (P) and Zn fertilizer sources and placements, with or without foliar supplements. A plot-based four-year field study was conducted on calcareous soils of contrasting texture (clay vs. sandy loam) in southern Manitoba from 2023 to 2024. Treatments included monoammonium phosphate (MAP), MAP + granular ZnSO4, and MicroEssentials® SZ® (MESZ) placed as broadcast-incorporated, side-band, or seed-row at seeding, with foliar Zn (± glycine betaine + salicylic acid; ± K) applied at Zadok’s growing stages Z12–15 and Z65. Plant nutrient concentrations were determined by ICP-MS following acid digestion, and Zn bioavailability was indexed by the phytic acid:Zn (PA:Zn) molar ratio. Across site-years, Zn fertilization increased grain yield by 8.3% over the Zn unfertilized control, with the highest yields achieved when MESZ was banded at seeding. Grain Zn responses depended on formulation, placement, and foliar supplementation. Seed-row MESZ plus foliar Zn produced the largest and most consistent grain Zn gains, raising concentration by ~27–60% at the two most responsive site-years and achieving ~41–43 mg kg-1. Depending on site-year, adding biostimulants provided small non-significant additional gains, whereas adding K produced no clear effect. Independent of formulation, banding MAP and MESZ generally outperformed broadcast for yield and Zn uptake. Grain PA:Zn ranged ~27–38 and improved (decreased ~25%) where foliar Zn was added to seed-row MESZ, but no treatment reduced PA:Zn below the conventional threshold of 15. Phosphorus fertilization did not systematically elevate grain phytic acid. Overall, integrating seed-row MESZ with well-timed foliar Zn is a practical path to raise grain Zn and improve PA:Zn under Prairie conditions. Further refinement should focus on foliar Zn rate/timing and context-dependent use of K and biostimulants to deliver consistent biofortification across soils and seasons. Future work should prioritize foliar Zn rate and timing and test compatibility with plant-health fungicides to simultaneously support yield and biofortification under Prairie conditions.February 202