Controlled-release fertilizer improved sunflower yield and nitrogen use efficiency by promoting root growth and water and nitrogen capacity

The traditional nitrogen fertilizer (TNF) is commonly adopted to achieve optimal crop yields, which often results in nitrogen loss and environmental pollution. Controlled-release fertilizer (CRF), renowned for their slow-release characteristics, offer a promising solution by better aligning with crop nitrogen requirements, thus mitigating nitrogen loss and enhancing agricultural productivity and nitrogen use efficiency (NUE). Nonetheless, despite their recognized benefits, understanding of the mechanisms underlying how CRF elevates soil NO 3 -N concentration (SNC) to facilitate root growth and improve NUE remains limited. This study was conducted in China's Hetao Irrigation Area during 2019–2020, and the results indicated that CRF outperformed TNF. It highlighted the significant impact of CRF on the interaction between soil and crops, particularly from the perspective of enhancing SNC to promote root development, thus improving root water and nutrient absorption capacities, which in turn increases NUE and yield. Notably, CRF significantly increased SNC. The results showed that compared to TNF treatments, the CRF treatments improved SNC, root surface area density (RSD), root dry weight (RDW), root sap production (RSPR), and NO 3 -N concentration in root sap (RSN) by 94.13 %, 12.62 %, 18.70 %, 6.15 %, and 13.94 % respectively. Most impressively, CRF increased nitrogen absorption efficiency to 17.76 kg/ha, leading to a sunflower yield of 3870.94 kg/ha. Structural equation modeling demonstrated that the fertilizer type and nitrogen application rate significantly influenced various crop growth indices. Specifically, these factors accounted for 20.0 %, 20.6 %, 77.6 %, 60.4 %, 72.3 %, and 66.6 % of the variance in RSD, RDW, nitrogen uptake, RSPR, RSN, and sunflower yield, respectively. This study advocate for the widespread and rational use of CRF, enhanceing crop yield and NUE by promoting root growth and nutrient and water absorption capabilities. This evaluation provides crucial evidence for agricultural practitioners to refine their fertilization strategies, ensuring increased crop yields and environmental protection. • CRF regulates SNC to enhance soil-plant interactions. • CRF optimizes N distribution to improve crop physiological functions and yield. • CRF modulates root physiological status to enhance resource utilization.