Impact of nitrogen application rates on wheat grain micronutrient concentration

This study aimed to evaluate how different nitrogen (N) fertilizer application rates affect the grain concentrations of key micronutrients zinc (Zn), iron (Fe), copper (Cu), and manganese (Mn) in bread wheat (Triticum aestivum L.), thereby addressing the nutritional quality challenges in calcareous (18–30%), Zn-limiting soils. Field trials were conducted over two years at three locations (Adana, Tarsus, and Kahramanmaraş) using a split-plot design with four wheat cultivars (Gökkan, Yakamoz, Altınöz, and Candaş) and five N levels (0, 7, 14, 21, and 28 kg N da−1) without micronutrient fertilization. Grain nitrogen concentration increased consistently with N rate at all sites (1.91–2.31% Tarsus; 2.13–2.46% Adana and 1.73–2.56% Kahramanmaraş), reaching up to 48.0% higher at 28 kg N da−1 in Kahramanmaraş compared to the control (p < 0.01). Micronutrient responses, however, were heterogeneous: Zn concentrations declined significantly with higher N (26.20–25.74 mg kg−1 Tarsus; 33.62–30.97 mg kg−1 Adana and 26.36–21.39 mg kg−1 Kahramanmaraş), especially in Kahramanmaraş (−18.9%, p < 0.01), whereas Fe (up to +23.4%) and Cu (+7–33%) increased across environments (p < 0.01). Importantly, Mn exhibited location-dependent variability, decreasing in Tarsus but increasing by 7.1% in Kahramanmaraş at the highest N rate. Among the cultivars, Yakamoz combined the highest Zn and N concentrations but showed the lowest grain yield. These findings highlight that N fertilization alone cannot reliably enhance micronutrient density in wheat grain. The contrasting responses, particularly the decline in Zn and the variable behavior of Mn, underscore the complexity of nutrient interactions and the need for integrated N-micronutrient management strategies to improve grain nutritional quality.