To elucidate the mechanisms underlying yield enhancement, efficiency improvement, and emission mitigation in rice-stubble wheat under the integrated “one basal plus one topdressing” mechanized deep fertilization strategy, a field experiment was conducted from 2021 to 2024 within a rice-wheat rotation system in Nantong, located in the lower Yangtze River Basin. The study employed a slow-release blended fertilizer (SRF, N∶P2O5∶K2O = 26∶12∶12) and conventional urea (U, 46% N), utilizing two self-developed machines: the 2BFGK-12(6)260 full-straw-stubble field clean-zone rotary-till intelligent fertilizer applicator and seeder, and the 3ZF-4(200) cultivator-topdresser. Seven fertilization regimes were established under a 30 cm + 15 cm wide-narrow row planting system. The control (CK) received four split applications of urea (N 240 kg hm-2; basal : tillering : jointing : booting = 5∶1∶2∶2, with basal application in narrow rows and topdressing broadcast across the field). Six reduced-N treatments (N 204 kg hm-2, a 15% reduction) were applied: M1 (100% SRF, narrow-row basal); M2 (60% SRF, narrow-row basal + 40% U, narrow-row broadcast at jointing); M3 (60% SRF, narrow-row basal + 40% U, wide-row banding at regreening); M4 (60% SRF, narrow-row basal + 40% SRF, narrow-row broadcast at regreening); M5 (60% SRF, narrow-row basal + 40% SRF, wide-row banding at regreening); and M4+5 (60% SRF, narrow-row basal + 20% SRF, wide-row banding + 20% SRF, narrow-row broadcast at regreening). The effects of these fertilization regimes on wheat yield performance, economic benefit, root morphological and physiological traits, nitrogen use efficiency (NUE), and N2O emissions were systematically evaluated. Compared with CK, treatments M2-M5 increased wheat yield by 4.0%-19.0% and economic returns by 13.7%-35.7%, with M4 and M5 showing optimal performance (yield increases of 14.1% and 19.0%; economic gains of 34.5% and 35.7%, respectively). These treatments significantly improved root traits, with root weight density increasing by 9.7%-111.8% and enhancements in root activity and oxidation capacity of 6.8%-52.0% and 4.2%-44.2%, respectively. Cumulative N2O emissions were reduced by 22.6%-34.5%, and soil NO3--N content in the 0-20 cm layer increased by 11.2%-40.0%. In terms of nitrogen utilization, M2-M5 treatments promoted grain N accumulation, post-anthesis N uptake, and its contribution to grain N content. Indicators of nitrogen use efficiency—including partial factor productivity, agronomic efficiency, and apparent recovery efficiency—increased significantly by 22.4%-40.0%, 29.7%-74.3%, and 9.41-18.77 percentage points, respectively. Notably, M4 and M5 achieved the most comprehensive benefits, with the greatest reductions in cumulative N2O emissions (27.0% and 34.5%) and consistently high apparent N recovery efficiency across two growing seasons (mean values of 43.5% and 46.8%), along with sustained root activity and topsoil inorganic N content during late growth stages. In contrast, M1 achieved the highest N2O mitigation (35.9%) but resulted in a 10.4% yield loss and 10.8% reduction in economic benefit, with unstable interannual variation in NUE. The optimized M4+5 treatment further enhanced root morphological and physiological traits while improving apparent N recovery efficiency and grain N accumulation. In summary, under a 15% nitrogen reduction (N 204 kg hm-2), split-application treatments using slow-release blended fertilizer (M4 and M5) achieved synergistic improvements in yield, economic return, nitrogen use efficiency, and N2O emission reduction, with the deep banding topdressing strategy (M5) delivering the most pronounced benefits. These findings provide strong theoretical support for the optimized and efficient use of slow-release fertilizers in nitrogen-reduced rice-wheat rotation systems.
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