Wheat nitrogen utilization efficiency and yield as affected by nitrogen management and environmental conditions
Nitrogen (N) is the main nutrient for plant nutrition, however, its fertilization management is still very complex. To evaluate wheat N utilization efficiency (NUtE) and yield in response to N fertilization management considering the influence of environmental conditions, an experiment was carried out in three field conditions in Southern Brazil: Londrina in rainfed and irrigation conditions, and Ponta Grossa in rainfed. A complete (2 × 2 × 2) + 1 factorial arrangement evaluated two N rates (40 and 80 kg ha-1), two N sources (ammonium nitrate and urea), two N timings of fertilization (at sowing or at the beginning of plant tillering), and additional treatment without N fertilization. Agronomic characteristics related to wheat productivity and N plant nutrition were evaluated. Irrigation increased the density of fertile spikes and the N accumulated in the shoot dry matter at anthesis, which partially explained the better grain yield in the irrigated condition. The higher N accumulation in the shoot dry matter was essential for grain yield increase in the environments with lower water deficit, based on their higher NUtE for grain yield. Nitrogen fertilization reduced NUtE for grain yield in Londrina (in rainfed and irrigation conditions), and increased NUtE for shoot dry matter production in all environments. In a colder condition (i.e. Ponta Grossa), the use of a higher N rate at sowing provided greater grain yield, thousand-grain weight, and density of fertile spikes. Nitrogen rate can be reduced in warmer and wetter environmental conditions that favor the mineralization of soil organic matter and the decomposition of soybean straw. The choice for urea or ammonium nitrate can be based on economic criteria in environments with low water deficit and low potential for NH3 volatilization. Nitrogen fertilization carried out exclusively at wheat sowing may be suitable to supply spring wheat N requirements.