Objectives To clarify the characteristics of nitrogen flux balance, nitrogen fertilizer use efficiency, and nitrogen loss thresholds (maximum environmentally permissible emissions) in maize fields of the Qingtongxia Irrigation District, Ningxia, and to establish a corresponding management system.

Methods From 2018 to 2023, total nitrogen input in maize fields across the irrigation district increased from 47800 t in 2018 to 65000 t in 2023, an increase of 35.83%, primarily due to a cropland expansion of 17100 hectares. Concurrently, environmental nitrogen emissions rose from 8900 t (18.70% of input) to 12100 t (18.55% of input), a 34.69% growth, with ammonia volatilization as the dominant pathway (accounting for 56.98% of total environmental emissions), followed by leaching (accounting for 26.54% of total environmental emissions) and runoff/erosion (accounting for 9.99% of total environmental emissions). The nitrogen fertilizer use efficiency in the irrigation district reached 42.92% in 2023, an increase of 5.72 percentage points compared with 2018. Notably, in Jinfeng District, ammonia volatilization risk decreased from 208% above the threshold (high risk in 2018) to low risk in 2023 through fertilizer reduction, while leaching risk was effectively controlled−by 2023, only Xixia District remained at low risk, and all other counties achieved risk-free status. Balanced fertilization combined with enhanced-efficiency fertilizers (S2) was identified as the optimal strategy. Compared with nitrogen reduction alone (S1), S2 increased nitrogen fertilizer reduction potential by 5.19−8.42 percentage points, improved use efficiency by 4.80−5.14 percentage points, reduced total environmental emissions by 44.13% (with all loss pathways below thresholds), and decreased environmental emissions by 52.50% while increasing nitrogen fertilizer use efficiency by 12.45 percentage points, compared with the 2023 baseline (S0).

Conclusions Integrating balanced fertilization with enhanced efficiency fertilizers, together with water saving engineering measures, can reduce all forms of nitrogen emissions below environmental thresholds in the Qingtongxia Irrigation District, representing a key technological pathway for achieving regional agricultural green development and nitrogen emission mitigation.