Nitrogen fertilizer strategies modulate gaseous nitrogen losses and improve maize yield and nitrogen use efficiency under saline-alkali stress in coastal reclaimed farmland

Abstract

Saline-alkali stress poses a growing threat to soil fertility and nitrogen (N) efficiency in coastal reclaimed farmlands, yet the interactive effects of salinity, alkalinity, and fertilization practices on gaseous N losses and crop performance remain poorly understood under field conditions. In this study, a two-year field experiment was conducted in Rudong County, eastern China, to evaluate how different N fertilizer strategies modulate ammonia (NH₃) volatilization, nitrous oxide (N₂O) emissions, maize yield, and N use efficiency under contrasting levels of saline-alkali stress. Five fertilization treatments, no urea (CK), urea alone (NU), urea with 3,4-dimethyl pyrazole phosphate (DMPP) (ND), urea with coated slow-release fertilizer (NUS), and urea with organic fertilizer (NUM), were applied in two field (S1, low saline-alkali stress; S2, high saline-alkali stress) with distinct salinity-alkalinity intensities. Results showed that high saline-alkali stress significantly increased N₂O and NH₃ emissions across all fertilization treatments, with cumulative N₂O emissions up to 75 % higher in field S2. Among the treatments, ND most effectively reduced N₂O emissions by 74.7 % (field S1) and 73.7 % (field S2), while NUM achieved the highest maize yield and apparent N recovery efficiency (RE_N), improving RE_N by over 16 % compared to NU. Compared with field S2, the maize yields in field S1 were higher by 16.8 %, 17.1 %, 7.8 %, 8.1 %, and 17.6 % under the CK, NU, ND, NUS, and NUM treatments, respectively. Stable isotope ¹⁵N tracing confirmed that NUM and NUS enhanced fertilizer N uptake and retention. Mantel test and Pearson correlation analyses revealed that soil enzyme activities and mineral N contents were key factors regulating NH₃ and N₂O emissions, as well as yield formation. Specifically, urease (UE), nitrate reductase (NR), and nitrite reductase (NiR) activities were positively correlated with NH₄⁺-N, NO₃^--N, and yield (p < 0.05), but also drove higher N gaseous losses. The study demonstrates that integrated N management strategies, particularly the use of organic fertilizer and nitrification inhibitors, can mitigate gaseous N losses and improve maize productivity in degraded saline-alkali farmland. The findings provide practical insights for designing resource-efficient fertilization schemes to ensure agricultural sustainability in coastal reclamation regions.