Soil nitrogen dynamics on a saline-alkali sunflower land under arid region in Western Inner Mongolia

Sunflower (Helianthus annuus L.), a dominant crop in Hetao Irrigation District, Western Inner Mongolia, is cultivated in arid and saline-alkaline fields due to their salt and alkali tolerance, ensuring that farmers’ income from these fields is not lower than those from fertile lands. However, little is known about the integrated analysis of nitrogen (N) dynamics, including soil total N (TN), nitrate (NO₃⁻), leachate TN and NO₃⁻, nitrous oxide (N₂O) fluxes, and N cycling microbial gene abundance in sunflower fields. The specific objective was to explore N dynamics for 2021 through 2023 in sunflower seeded to saline-alkali croplands under arid condition based on treatments of irrigation rate (I rate: I1, 5110; I2, 4050; I3, 2985 m³ ha⁻¹) for washing salinity by irrigation and nitrogen fertilization rate (N rate: N1, 750; N2, 600; N3, 450; N0, 0 kg ha⁻¹). Our findings indicated that I rate did not affect soil N dynamics; N rate significantly increased soil TN, NO₃⁻ and N₂O fluxes, especially showing an extremely significant increase for leachate TN and NO₃⁻ leachate. The interaction of I and N rates impacted soil TN, NO₃⁻, their leachate, and N cycling microbial gene abundances, especially denitrification genes. Soil leachate TN and NO₃⁻ increased exponentially over time. Soil N₂O fluxes increased annually with the growth of sunflowers. In the saline-alkali sunflower fields, low N rate (450 kg ha ⁻¹) can be an optimal strategy, and the precise calibration of I and N rates can guarantee adequate N dynamics and yields, highlighting the intricate balance required for sustainable agricultural practices.