Influence of long-term nitrogen fertilization on crop and soil micronutrients in a no-till maize cropping system

Sustaining or increasing micronutrient concentrations in food and feed is essential for human and animal health, yet little research has quantified the relative importance of nitrogen (N) fertilization on maize micronutrient concentrations. Nitrogen fertilization could dilute some micronutrients while increasing others (i.e., biofortification). Nitrogen fertilization also influences the amount of residue returned to the soil, potentially altering soil organic carbon (SOC) and micronutrients. While changes in soil micronutrients under long-term production are sometimes attributed to export via harvest or import via fertilization, available micronutrients are also influenced by soil organic matter - changes in SOC could impact available micronutrients. Our objectives were to (1) examine the long-term effects (14 years) of different N rates (0, 68, 120,173, 232 kg ha−1) on the concentration ([]), uptake, and cycling of N and micronutrients (Fe, Zn, Cu, Mn) in no-till continuous maize and (2) assess whether nutrient removal via grain harvest, or residue return have resulted in depletion or accumulation of SOC and available and total micronutrients. Results showed a positive impact of fertilization on stover [N], [Cu] and [Mn], and increased grain [N] and [Fe]. However, fertilization decreased [Zn] in all plant fractions, indicating that maize [Zn] is susceptible to yield dilution. Total and available soil micronutrients were not impacted by fertilization, despite widely differing rates of nutrient harvest and return. Available Cu and Mn followed changes in SOC, which declined in all depths except the surface 0-7.5 cm. Available Zn increased in the surface 0-7.5 cm, with slight increases in deeper depths. Available micronutrients appear to be closely regulated by SOC in this system. These findings give additional insights into how N fertilization impacts maize micronutrient concentrations, and suggest that SOC contributes to micronutrient availability, underscoring the role of SOC in sustaining long-term soil fertility.