Relative Performance of Urea and Nano-urea in Conjunction with Zinc Fertilization on Growth, Productivity, and Nitrogen Use Efficiency in Spring Wheat

Nano-fertilizers possess a substantial promise in modern agriculture for nutrient utilization efficiency and minimizing environmental impact. However, limited information exists regarding the relative performance of nano-urea, and urea with nano-zinc or other zinc (Zn) fertilization strategies. A two-year (winter seasons of 2021–22 and 2022–23) field experiment was carried out through a split-plot design to evaluate the efficacy of combined effects of nitrogen (N) sources: urea ± nano-urea, microbial inoculation and Zn fertilization, particularly, nano-urea and zinc in terms of growth, yield, nitrogen uptake, and use efficiencies of wheat. In 2021–22 and 2022–23, the application of N₁₃₀ kg ha⁻¹ increased wheat grain yield by 23.2% and 33.1%, respectively compared to the control plot. In contrast, employing 97.5 kg ha⁻¹ and 65 kg ha⁻¹ of N along with two foliar sprays of nano-urea at the rate of 2.5 l ha⁻¹ reduced yields by 3.4–7.8%, 6.8–12.4% in both years of the study in comparison to N₁₃₀ kg ha⁻¹. Foliar spray of 0.1% nano-ZnO at maximum tillering, anthesis, and grain filling stages enhanced yield by 3.7–4.5% when compared to no Zn. Nitrogen uptake ranged from 101.8–110.5 kg ha⁻¹ in grain and 49.1–52.0 kg ha⁻¹ in straw with N₁₃₀ kg ha⁻¹. When N levels were reduced to 97.5 kg ha⁻¹ + Nano-N and 65 kg ha⁻¹ + Nano-N decreased uptake in grain by 6.6–10.6% and 17.8–23.6%, respectively. Further, foliar sprays of 0.1% nano-ZnO increased N uptake by 7.2–8.1 kg ha⁻¹ compared to plots without zinc application in both years. Among N sources, the application of N₁₃₀ kg ha⁻¹ has resulted in improved yields, N content and uptake. Within Zn fertilization, the application of 0.1% nano-ZnO foliar spray resulted in increased wheat yields and nitrogen uptake. However, using 50% of the recommended nitrogen (N₆₅ kg ha⁻¹) with two foliar applications of nano-urea at the rate of 2.5 l ha⁻¹ reduced the grain yields to the tune of 7.8–12.4% due to inadequate nitrogen content. Nano-urea has failed to fulfill the N demand required for increasing the wheat yield and needs comprehensive validation. In conclusion, it is recommended to apply 130 kg N ha⁻¹ in three splits along with 0.1% foliar sprays of nano-Zn oxide during the maximum tillering, anthesis, and grain filling stages for enhancing grain and straw yields, as well as improving nitrogen content, uptake and its efficiency.