Single application of controlled-release fertilizer at the seedling stage enhances grain yield and mitigates methane emissions in coastal saline soils

Introduction Rice cultivation in coastal saline soils is critical for global food security. However, optimizing nitrogen (N) fertilizer strategies in these environments to enhance yield and reduce greenhouse gas emissions, particularly methane (CH 4 ), remains a challenge. This study investigates the effects of controlled-release fertilizers (CRF) on rice yield and CH 4 emissions in coastal saline soils. Methods A two-year (2023–2024) field study was conducted using two rice cultivars, Nanjing 5718 and Yongyou 4953, under four different nitrogen treatments: N0 (zero N), N1 (conventional split urea), N2 (50% 80-day CRF + 50% basal urea), and N3 (50% 120-day CRF at seedling + 50% basal urea). Grain yield and CH 4 emissions were measured, and root morphological traits were also assessed. Results The N3 treatment significantly increased grain yield by 10.2 to 12.9% compared to N1, while N2 reduced yield by 11.9 to 13.0%. CH 4 emissions were highest under N1 and decreased under N2 and N3 treatments. Specifically, N2 reduced peak CH 4 flux by 18.9% and total emissions by 20.4%, while N3 reduced peak flux by 6.8% and total emissions by 7.7%. Root development was enhanced under N3, with significant increases in root length, surface area, and oxidation activity. Discussion The application of CRF, especially with a 120-day release period at the seedling stage, improved rice grain yield and mitigated CH 4 emissions. These results suggest that CRF provides a promising strategy for sustainable rice cultivation in coastal saline soils, with the added benefit of reducing environmental impact.