Nitrogen fertilization strategies for improved Mediterranean rainfed wheat and barley performance and water and nitrogen use efficiency

Adequate fertilization strategies are paramount to fulfill increasing demands for food, feed and fiber while reducing environmental impacts. However, their optimization under Mediterranean no-till systems has received little attention. The objective of this work was to assess winter cereal yield and water and N use efficiencies in a rainfed semiarid Mediterranean climate under (i) a range of pre-plant fertilizers [control without N fertilizer (0 N), and the following at 75 kg N ha⁻¹: mineral N (MIN), swine slurry (SS), poultry manure (PM), and compost (COM)], (ii) fertilizer incorporation: no-tillage without incorporating (NT) or incorporation with a vibrocultivator (INC) and (iii) application of urea-ammonium nitrate solution (UAN) as top-dress as a control without UAN (UAN-) or 50 kg N ha⁻¹ (UAN+). The experiment covered six cropping seasons (2012–2019). Pre-plant applications had similar responses in crop yield, biomass, N uptake, grain N, water-use efficiency for biomass (WUE_b), and water-use efficiency for yield (WUE_y) but were greater than 0 N. The lack of differences between pre-plant fertilizers would be explained by the high amount of residual N and the mineralized N during the crop cycle. Top-dress UAN increased WUE_y and crop yield in all the cropping seasons by an average of 587 kg grain ha⁻¹, which represented 18 % of the total annual production. Averaged across variables and the growing seasons, INC reduced soil water content and WUE_b by 10 % (from 24.3 to 21.8 kg ha⁻¹ mm⁻¹). Also, INC reduced grain yield by 9% (from 3799 to 3450 kg ha⁻¹) by reducing the number of spikes m^-2 produced, pointing out that INC resulted in water deficit during the early reproductive period of the crop. While INC is often consider a best management practice to reduce NH₃ volatilization losses from broadcast fertilizer applications, the results demonstrate that in rainfed Mediterranean agroecosystems water is more limiting than the N that could be potentially lost by volatilization.