Slow-release fertilizers mitigate brackish water stress in rice: Boosting yield and nitrogen use efficiency in saline soils

Rice cultivation with brackish water irrigation represents an effective practice to ameliorate coastal saline soils, while the application of slow and controlled release fertilizers (SCRFs) further mitigates its adverse effects on nitrogen (N) use efficiency. This study conducted a field soil column experiment with coastal saline soils (soil salinity: 2.20 g kg⁻¹) to evaluate the combined impact of brackish water irrigation (fresh water: 0.15 g L⁻¹, brackish water: 1.00–1.50 and 1.35–2.00 g L⁻¹) and N fertilizer types (urea, polyurethane-coated urea (PCU), and urea formaldehyde) on rice yield and N use efficiency, addressing the critical challenge of water-fertilizer management in coastal saline regions. Results showed that compared with fresh water irrigation, brackish water irrigation significantly inhibited the growth of rice root, leading to a significant reduction in root morphological characteristics(P < 0.05). This inhibitory effect was particularly pronounced under the higher salinity treatment (W3). These reductions impaired nutrient and water absorption, leading to a decrease in crop yield and agronomic nitrogen use efficiency (ANUE) (P < 0.05). The application of SCRFs significantly promoted the development of fine root systems. Root length, tip number, branch number, and cross number under the SCRFs treatments were significantly higher than those under the urea treatment (P < 0.05). As a result, SCRFs mitigated the negative effects of brackish water irrigation on rice yield and ANUE. Overall, our key practical recommendation for rice cultivation in coastal saline regions is as follows: irrigating with brackish water of salinity below 1.5 g L⁻¹, combined with basal application of PCU. This integrated water-fertilizer management strategy not only optimizes the utilization of unconventional brackish water resources but also enhances N fertilizer efficiency while ensuring stable crop yields. Thus, it provides a science-based and feasible practice for the sustainable utilization of coastal saline soils.