Durum Wheat Yield and N Uptake as Affected by N Source, Timing, and Rate in Two Mediterranean Environments

In Nitrate Vulnerable Zones (NVZ) site-specific techniques are needed to match N availability with durum wheat (Triticum turgidum subsp. durum Desf.) requirements. Slow-release fertilizers can improve efficient N supply and reduce leaching, thus contributing to sustainable agriculture. To study the effects of rates, sources and timings of nitrogen application, two-year field experiments were carried out in two Mediterranean NVZs of Central Italy (Pisa and Arezzo). The trial compared: i) two N rates: one based on the crop N requirements (NO), the other on the Action Programmes’ prescriptions of the two NVZ (NAP); ii) three N sources: urea, methylene urea, and nitrification inhibitor DMPP; iii) two top-dressing times: BBCH21 and BBCH31. Grain yield, yield components were determined, together with N uptake. Results showed that: i) grain and biomass production were reduced with NAP at both locations; ii) urea performed better than slow-release fertilizers; iii) the best application time varied depending on the N source, as slow release fertilizers achieved higher yield when applied earliest (BBCH21) at both locations, while urea performances differed between locations (BBCH31 was better at Pisa and at BBCH21 at Arezzo). Different behaviors of top-dressing fertilizers at the two localities could be related to the diverse patterns of temperatures and rainfall. Therefore, optimal fertilization strategies vary according to environmental conditions.