Wheat grain micronutrients and relationships with yield and protein in the U.S. Central Great Plains

Wheat (Triticum aestivum L.) provides ~ 20% of the calories consumed by a growing global population yet is inherently low in Zinc (Zn) and Iron (Fe). Continued yield gains have inadvertently reduced grain [Zn] and [Fe] (brackets denote concentration, mg kg-1), with negative human health impacts. It is unclear if grain [Fe] or [Zn] of high-yielding modern varieties meet nutritional micronutrient targets. Nitrogen (N) fertilization may synergistically offset yield dilutions and improve grain micronutrients, yet this has not been evaluated in the U.S. Central Great Plains, a region with limited available soil Zn (Znavail). To determine how factors like soil fertility, yield, variety, and fertilization impact grain [Zn] and [Fe], we measured available soil micronutrients and factors that can influence Znavail at six sites in the Central Great Plains. We measured grain yield, protein/N%, and nutrients of three modern wheat varieties grown under two N fertilization regimes. Soil Znavail was critically low at all sites, highlighting the need to re-examine sufficiency guidelines. Grain [Zn] was well below target concentrations at all sites, while grain [Fe] was within 5 mg kg-1 of human nutrition targets. Grain [Zn] declined by ~ 0.8 mg kg-1 for each 1000 kg ha-1 yield, whereas grain [Fe] declined by ~ 2.3 mg kg-1 per 1000 kg ha-1 yield increase, with little varietal difference in yield-adjusted [Zn] and [Fe]. Across sites, N fertilizer only slightly increased grain [Fe] and [Zn] (1.7 and 0.9 mg kg-1, respectively), suggesting that this is not an effective biofortification strategy in these systems. Additional strategies for biofortifying wheat grain [Zn] are required in this region.