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

Authors: Miner, Grace; Delgado, Jorge; IPPOLITO, JAMES - Colorado State University; JOHNSON, JERRY - Colorado State University; KLUTH, DANICA - Colorado State University; Stewart, Catherine

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2022
Publication Date: 1/28/2022
Citation: Miner, G.S., Delgado, J.A., Ippolito, J.A., Johnson, J.J., Kluth, D., Stewart, C.E. 2022. Wheat grain micronutrients and relationships with yield and protein in the U.S. Central Great Plains. Field Crops Research. 279. Article e108453. https://doi.org/10.1016/j.fcr.2022.108453.
DOI: https://doi.org/10.1016/j.fcr.2022.108453

Interpretive Summary: Wheat supplies around 20% of the calories consumed globally, but this crop is low in the micronutrients Zinc (Zn) and Iron (Fe). These micronutrients are needed in the human diet in small amounts, yet billions of people suffer from micronutrient deficiencies. Unfortunately, decades of breeding wheat for high yields has resulted in unintended additional declines in grain [Zn] and [Fe] (brackets denote concentration, mg kg-1), because grain micronutrients typically decline as crop yields increase. Additionally, when wheat is grown in Zn- or Fe-deficient soils, grain micronutrients can be too low to meet the target range for human health. Colorado is a major wheat-producing region in the Central Great Plains, yet there are multiple soil factors limiting Zn and Fe availability in this region. It is unclear if grain [Fe] or [Zn] of high-yielding varieties grown here meet nutritional targets. Some studies have suggested that Nitrogen (N) fertilizer applied to improve yields or protein can have positive impacts on grain [Zn] and [Fe] that may offset yield declines, but this has not been evaluated in the Central Great Plains. To determine how basic factors like soil fertility, yield, variety, and fertilization impact grain [Zn] and [Fe], we measured soil micronutrients and other soil factors at six sites. We measured grain yield, protein, and nutrients of three wheat varieties grown under two N fertilization regimes. Soil available Zn was critically low at all sites. Grain [Zn] was well below target concentrations, and at some sites was only half of the nutritional target of 25 mg kg-1. Grain [Fe] was generally at, or within 5 mg kg-1 of, the nutrition target of 30 mg kg-1. Grain [Zn] declined by ˜ 6 mg kg-1 over a yield difference of 4000 kg ha-1 DM, whereas grain [Fe] declined by ˜ 15 mg kg-1, with little difference in [Zn] and [Fe] between varieties. Across sites, N fertilizer only slightly increased grain [Fe] and [Zn]. This research indicates that additional strategies for biofortifying wheat grain with Zn are required in the Central Great Plains and highlights the need to re-examine soil micronutrient sufficiency guidelines.

Technical Abstract: 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 significant negative human health impacts. It is unclear if grain [Fe] or [Zn] of high-yielding varieties meets nutritional micronutrient targets. Nitrogen (N) fertilization may synergistically offset yield dilutions and improve grain micronutrients, yet this has not been evaluated in agroecosystems with limited available soil Zn (Znavail). To determine how basic factors like soil fertility, yield, variety, and fertilization impact grain [Zn] and [Fe], we measured soil micronutrients and factors that can influence Znavail (e.g., pH, SOC%, Phosphorus (P)) at six sites in the Central Great Plains. We measured grain yield, protein/N%, and nutrients of three modern 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 nutrition targets. Grain [Zn] declined by ˜ 6 mg kg-1 over a yield difference of 4000 kg ha-1 DM, whereas grain [Fe] declined by ˜ 15 mg kg-1 with little varietal difference in yield-adjusted in [Zn] and [Fe] (<2 mg kg-1). Across sites, N fertilizer only slightly increased grain [Fe] and [Zn] (1.7 and 0.9 mg kg-1, respectively). Additional strategies for biofortifying wheat grain Zn are required in the Central Great Plains.