It remains unclear how the source and rate of nitrogen (N) fertilizers affect N₂O concentration and effluxes along the soil profile under the drip-fertigated agricultural system. A plot-based field study was performed in 2017 and 2018 in a cotton field in arid northwestern China, with an objective to elucidate the impact of the applications of conventional urea (Urea), polymer-coated urea (ESN) and stabilized urea (SuperU) at rates of 120 and 240 kg N ha⁻¹ on concentration and efflux of N₂O in the soil profile and its relationship with N₂O surface emissions. The in-situ N₂O concentrations at soil depths of 5, 15, 30 and 60 cm were measured and used to estimate soil profile N₂O effluxes. Estimates of surface N₂O flux using the concentration gradient-based (GM) were compared with those measured using the chamber-based (CM) method. In both years, soil N₂O concentrations at all depths increased in response to basal N application at planting or in-season fertigation events. However, N rate or source did not affect soil N₂O concentrations or effluxes at each depth. Surface emissions of N₂O were mostly associated with that presented in the top layer of 0–15 cm. Surface N₂O efflux determined by GM was poorly or not associated with those of chamber measurements, which was attributed to the low N₂O production restricted by soil moisture condition under the drip-fertigated condition. These results highlight the challenge of applying the enhanced efficiency N fertilizer products in the drip-fertigated agricultural system.

Vegetable production in solar greenhouses in northern China results in the excessive use of nitrogen (N) fertilizers and water via flooding irrigation. Both factors result in low N use efficiency and high environmental costs because groundwater becomes contaminated with nitrate (NO3−). Four consecutive tomato (Lycopersicum esculentum Mill.) cropping seasons were tested whether drip fertigation and/or the incorporation of maize straw (S) may significantly reduce NO3− and dissolved organic N (DON) leaching while increasing the water-use efficiency (WUE) and partial factor productivity of applied N (PFPN) of the tomatoes. The following treatments were used: ① conventional flooding irrigation with overfertilization (CIF, 900 kg N ha−1 season−1), ② CIF + S, ③ drip irrigation with optimized fertilization (DIF, 400 kg N ha−1 season−1), ④ DIF + S. We found that (1) DIF significantly increases the PFPN and WUE by 262% and 73% without compromising the yield compared with CIF, respectively. (2) For CIF, approximately 50% of the total N input was leached at a NO3−/DON ratio of approximately 2:1. (3) Compared with CIF, DIF reduced NO3− and DON leaching by 88% and 90%, respectively. Water percolation was positively correlated with N leaching (p < 0.001). (4) Straw application only reduced NO3− leaching losses in the first year and did not affect DON leaching overall, although DON leaching was increased in DIF in the first growing season. In conclusion, DIF significantly reduces NO3− and DON leaching losses by approximately 90% compared with the current farmer practice (CIF). Considering the significant DON leaching losses, which have been overlooked because previous measurements focused on NO3−, DON should be considered as a primary factor of environmental pollution in conventional solar greenhouse vegetable production systems.