Closing the yield gap of spring maize by synergizing drip nitrogen-fertigation with plant density in the arid region of Northwest China

Drip fertigation technology combined with optimal plant density (PD) and nitrogen application rate (Nrate) management is a critical strategy for closing the yield gap in arid regions of Northwest China. A three-year field experiment (2021–2023) was conducted in Hetao Irrigation District (HID) to determine the effects of PD and Nrate on crop growth, grain yield (GY), water productivity (WP), radiation use efficiency (RUE), and nitrogen use efficiency (NUE) of drip-fertigated spring maize ( Zea mays L.). Four plant densities (D1: 60,000 plants hm −2 , D2: 75,000 plants hm −2 , D3: 90,000 plants hm −2 , D4: 105,000 plants hm −2 ) and three N application rates (N1: 200 kg hm −2 , N2: 250 kg hm −2 , N3: 300 kg hm −2 ) were considered. Separate annual analyses indicated PD as the main factor governing population establishment and resource utilization, with a greater effect size than Nrate and their interaction. Increasing density from D1 to D3 significantly enhanced plant height (H VT ), leaf area index (LAI VT ), population-level aboveground dry matter (DM P ), and nitrogen uptake (Nut P ) by 6.30 %, 52.8 %, 21.0 %, and 11.2 %, respectively, ultimately rising GY by 28.9 %. The D3N3 achieved the highest DM P and Nut P , exceeding other combinations by 17.0 % and 16.4 %, while D3N2 resulted in optimal GY, WP, and RUE, exceeding other combinations by 14.5 %, 16.5 %, and 10.2 %. However, a further increase to D4 induced negative effects, reducing DM P , Nut P , GY, WP, and RUE by 6.80 %, 14.0 %, 4.33 %, 8.98 %, and 5.19 %, respectively, although NUE improved by 11.2 %. Linear mixed models also confirmed the dominant role of density. Although the PD×Nrate interaction was not statistically significant, the Nrate effect varied with PD environment. Specifically, N3 suppressed plant growth at D1, limiting H VT , LAI VT , and DM P . Moderate N2 resulted in optimal GY, WP, and RUE at densities from D1 to D3, whereas at D4, increasing Nrate exhibited a consistently positive effect. On the basis of bivariate regression analysis, the optimal combination was 93,000 plants hm −2 with 264 kg N hm −2 , which could achieve a GY and a WP of 20.5 t hm −2 and 4.31 kg m −3 , respectively, and reduce the yield gap from 72.0 % to 18.0 %. Overall, these findings show that prioritizing planting density and implementing density-specific nitrogen management are the pivotal strategies for closing the yield gap and achieving high resource use efficiency in drip-fertigated spring maize of Northwest China.