To address sustainability challenges in the North-Western Indo-Gangetic Plains (NW-IGP), conservation agriculture and diversification from rice to maize have been promoted. However, nitrogen (N) management under conservation agriculture remains largely similar to conventional practices, resulting in limited improvements in nitrogen-use efficiency (NUE) and often yielding results comparable to conventional tillage. This study explores alternative N management strategies for conservation agriculture that sustain maize yields, improve soil quality, reduce N losses, and increase net returns. A 40-year simulation using the DSSAT-CERES-Maize model was conducted to evaluate long-term impacts. The field experiment compared surface residue-retained zero tillage and residue-incorporated conventional tillage with three beneath-the-surface-placed (point/band) N application rates (100, 125, and 150 kg ha(-1)) and respective controls (0 kg N ha(-1)), alongside a no-residue farmers' practice with surface-broadcasted 150 kg N ha(-1). The model effectively captured the dynamics of key growth and harvest parameters, including phenology, biomass, and was applied to assess the long-term sustainability of these practices. Results revealed that zero tillage (5416 kg ha(-1)) outperformed conventional tillage and farmers' practice, with 6.6% and 28% higher grain yields over 40 years and demonstrated greater resilience during drought and high-rainfall years. Zero tillage with 125 kg N yielded nearly the same as 150 kg, indicating N input can be reduced by 25 kg ha(-1) (similar to 17%) without yield loss. After 40 years, soil organic carbon in the top 20 cm increased to 0.77% in zero tillage, compared to 0.59% in conventional tillage and 0.43% in farmers' practice. Economically, 125 kg N ha(-1) under zero tillage yielded returns comparable to 150 kg N ha(-1) under current and reduced fertilizer subsidy conditions, and outperformed under no-subsidy conditions. Thus, reducing the recommended N dose from 150 to 125 kg ha(-1) under zero tillage sustained maize yields and returns while enhancing soil carbon and NUE in the NW-IGP.