Optimized application of controlled-release nitrogen improves grain yield, nitrogen use efficiency, and lodging resistance in rice

Lodging is a primary factor limiting rice grain yield. Achieving synergistic improvements in grain yield and nitrogen use efficiency (NUE) without increasing lodging risk has been a global research priority. In this study, two rice cultivars - Yongyou 2640 (indica–japonica hybrid rice) and Jinxiangyu 1 (inbred japonica rice) - were evaluated in field experiments conducted over two growing seasons. Six nitrogen management strategies were implemented: no nitrogen (T1), conventional urea (T2), controlled-release nitrogen (CRN) (T3), reduction of CRN (T4), CRN combined with single basal application of conventional urea (T5), and CRN combined with split applications of conventional urea (T6). Compared with T2, the integrated nitrogen strategies (T5 and T6) increased NUE by 4.89–5.69% and grain yield by 3.41–4.65%. These treatments also enhanced structural integrity of the second basal internode, evidenced by increased carbohydrate content, internode breaking strength, epidermal silicon layer thickness, number of large and small vascular bundles, and thickness of both parenchymatous and mechanical tissues. Concurrently, internode length, bending moment, and lodging index were reduced. Collectively, these findings indicate that integrating CRN with conventional urea improves morphological, mechanical, physicochemical, and anatomical properties of the second basal internode, thereby enhancing stem strength and enabling high yield and NUE without compromising lodging resistance.