Iron biofortification and yield of wheat grain in response to Fe fertilization and its driving variables: A meta-analysis

Iron (Fe) is an essential micronutrient for human nutrition and health, but its deficiency is prevalent worldwide. Wheat biofortification offers a potential strategy to alleviate micronutrient deficiencies in humans. However, the effects of Fe fertilization on grain Fe concentration and yield of wheat remain inconsistent. A global meta-analysis of 107 publications including 171 records of grain Fe concentration and 378 records of yield was conducted to quantify the contribution of Fe fertilization to wheat biofortification. Overall, compared with no Fe addition, Fe application significantly increased grain Fe concentration by 20.5% and yield by 12.4%. Foliar and soil application of Fe fertilizer increased grain Fe concentration by 18.2% and 26.7%, and grain yield by 15.1% and 9.5%, respectively. Results showed that higher foliar Fe fertilizer rate (>0.1%) and multiple applications before the flowering stage had a stronger effect on grain Fe concentration than lower Fe fertilizer rate (<0.1%) and only one application after flowering stage. Under severe soil Fe deficiency conditions (DTPA-Fe < 6 mg kg⁻¹), the foliar application increased yield by 13.9%, more than the yield increase (4.0%) when soil DTPA-Fe was greater than 6 mg kg⁻¹. Soil application of Fe was more effective to improve yield and grain Fe of wheat grown on high pH soil with lower available Fe. Furthermore, there was a positive relationship between the increase in the wheat grain yield and the increase in grain Fe concentration. In summary, our findings indicate that Fe fertilization can be managed in ways that simultaneously enhance grain nutritional quality and achieve high wheat yields.