Effect of Foliar Application of Micronutrients and Fungicides on the Nitrogen Use Efficiency in Winter Wheat

The increase in the grain density (GD) is the key factor for effectively controlling Nitrogen-Use Efficiency (NUE) in winter wheat. Winter-wheat protection with fungicides and/or foliar fertilization with micronutrients during the critical stages of yield formation affects the grain yield by increasing GD. This hypothesis was verified in a two-factor field experiment, carried out in the 2013/2014, 2014/2015, 2015/2016 growing seasons. A field experiment in a two-factor split-plot design, included three systems of wheat foliar protection (FP): (i) N + Mi (N + macronutrients), (ii) N + P (N + fungicides), (iii) N + Mi + P, and 0, 40, 80, 120, 160, 200, 240 kg N ha−1. The grain yield, despite the significant effect of years, depended on the interaction of FP and N doses. The maximum yield of 8.1, 10.7, 11.1 t ha−1 for the optimal N dose of 79.8, 227.4, and 245.2 kg ha−1, was achieved, respectively, for N + Mi, N + N, N + Mi + P. The wheat-grain yield depended significantly on GD (R2 = 0.98, p ≤ 0.001). Wheat protected with fungicides increased GD gradually with the N dose, reaching over 3000 grains per m2 when fertilized with 200 kg N ha−1. The lack of fungicide protection, reducing GD, consequently resulted in a greater accumulation of N in straw at the expense of grain. Fungicide protection of wheat through the positive effect on N management by wheat should be considered as an agronomic measure that supports N-Use Efficiency.