Optimized irrigation management mitigates reactive nitrogen loss and shapes nitrogen fate in wheat production

Context: Optimized irrigation management plays a pivotal role in wheat production in the North China Plain (NCP). However, there exists limited research on the potential impact of different irrigation regimes on the loss of reactive nitrogen (Nr) and the fate of nitrogen (N) within the wheat-soil system. Objective: Our study involved an irrigation experiment aimed at quantifying nitrogen-reducing (Nr) while tracing the N fate. Our primary objective was to glean insights into improving nitrogen use efficiency (NUE) and reducing N surplus, thereby enhancing crop yields and minimizing environmental risks. Methods: A two-year field experiment involving winter wheat (Triticum aestivum L.) was conducted in the NCP, employing four distinct irrigation management strategies: I0, pre-planting irrigation; I1, pre-planting + jointing irrigation; I2, pre-planting + anthesis irrigation; I3, pre-planting + jointing + anthesis irrigation. Throughout the wheat growth stages, we measured soil NH3 and N2O emissions alongside yield assessments. The Nr loss, N surplus, NUE and Nr footprint were evaluated. Results: Among the components contributing to Nr loss, ammonia (NH3) volatilization was the most significant, accounting for 53.1-58.9%, followed by nitrate (NO3-) leaching (18.9-23.2%), indirect Nr loss (10.9-12.7%), nitric oxide (NO) emission (4.90-6.02%), nitrous oxide (N2O) emission (2.52-3.55%), and ammonium (NH4+) leaching (2.10-2.58%). NH3 emission and Nr loss demonstrated a close association with soil moisture levels influenced by irrigation management. Across all treatments, the primary fate of the N input was N uptake, representing 42.7-59.4%, and N surplus, accounting for 28.4-46.0%. Furthermore, NH3 volatilization, as the leading contributor to total N loss (11.4-12.9% of N input), accounted for 5.70-6.80% of N input. Compared to over-irrigation (I3), the I1 treatment, characterized by supplemental irrigation during the jointing stage, exhibited a remarkable 29.0% (P < 0.05) reduction in N surplus, achieved a higher NUE of 59.4%, and sustained wheat yield, thereby minimizing the Nr footprint. Conclusions: Our findings highlight that supplementary irrigation at the jointing stage effectively mitigates Nr loss and shapes the N fate, resulting in both high NUE and increased wheat yields, while simultaneously reducing the Nr footprint.