Single-side nitrogen banding increases rice yield and nitrogen use efficiency by promoting asymmetric root–soil nutrient interactions

Root-zone nitrogen (N) banding is widely used to improve N use efficiency in crops. However, the effect of lateral fertilizer placement on rice performance remains unclear. We conducted two-year field experiments (2023–2024) in China, with a multi-variety validation trial at a second site, comparing single-side banded fertilization (BF-S, urea placed 5 cm deep and 5 cm lateral to one side of the plant row) against symmetrical double-side banding (BF-D) and conventional surface broadcasting. BF-S achieved 13.0% higher grain yield (9.2 vs 8.1 t ha −1 ) and 57.1% higher N recovery efficiency (NRE, 56.1% vs 35.7%) than BF-D, with consistent advantages across four rice varieties. The higher performance of BF-S was associated with a pronounced lateral heterogeneity of NH 4 + that persisted for approximately 30 d after transplanting, accompanied by preferential root growth toward the fertilized zone. Multivariate analyses showed that grain yield and NRE were more closely related to subsurface NH 4 + availability and its spatial asymmetry than to root architectural traits. Consistent patterns of NH 4 + heterogeneity and root lateral asymmetry were also observed across sites and varieties in the validation experiment. These results highlight the importance of spatial nutrient heterogeneity in paddy N management and suggest that single-side banding is a promising fertilization strategy for improving rice productivity and N use efficiency.