Efficient nitrogen (N) fertilizer management is critical for wheat production and the long-term protection of the environment. Given the importance of durum wheat for the Italian economy, its environmental implications need to be investigated for designing sustainable production system. Three concurrent experiments were carried out in Gravina in Puglia (Apulia, southern Italy) to investigate the agronomic and environmental response of rainfed durum wheat (Triticum turgidum L., var. durum) to different N rates, N source and application time over three years (2010-2012). In the three experiments, the following parameters were analyzed: grain yield, yield components (i.e. harvest index, spikes m(-2)), quality traits (i.e. hectoliter weight, protein content), energy input/output analysis including the calculation of energy indexes and greenhouse gas (GHG) emissions. The N rate experiment included rates of 45, 90 and 135 kg N ha(-1). Each rate was split in various proportions between sowing, tillering and stem elongation. For the experiment on N timing and splitting, a single dose of 90 kg N ha(-1) was split between sowing, tillering and stem elongation at different fractions (0-90-0; 40-50-0; 10-40-40). The N fertilizer source experiment tested the effect of the application of 90 kg N ha(-1) of urea split at sowing and tillering (12-78-0) on the investigated parameters, and compared to Entec (R) 26 and Sulfammo 23 with the same does and application time. Nitrogen agronomic efficiency (NAE) was also calculated to assess the potential yield increase in response to different N fertilizer rates and types. The results showed that N rate, N source and the application time had a significant impact on grain yield, grain protein content, energy output and GHG emissions under normal weather conditions. Considering the site-specific condition, the overall results revealed that the split application of 90 kg N ha(-1) during three growth stages gave favorable results in terms of grain yield and quality, and optimizes NAE with less environmental impact. The effectiveness and efficiency of this strategy was more pronounced when two-third of the full N dose was applied at later stages (tillering and stem elongation). This strategy found to be more effective in improving wheat yield and quality than the increase in the N rate, which could offer the potential to decrease N fertilization rate in wheat production. This study provides useful information for farmers on how to manage the N fertilization of wheat for sustainable production system. (C) 2017 Elsevier Ltd. All rights reserved.
