Maize yield, crop water productivity, and partial factor productivity of nitrogen influenced by nitrogen rates and groundwater table depths: A lysimeter study in the North China Plain

Falling groundwater table depth (WTD) and excessive nitrogen (N) fertilization have caused both crop yield reductions and environmental contamination. However, the combined effects of WTD and N application rate on maize production and resource use efficiency remain unclear. In this study, an automated groundwater level control system was used to investigate the impacts of WTDs (2 m and 4 m) and N rates (210 and 280 kg ha^–1) on soil properties, yield components, crop evapotranspiration (ET_c), crop water productivity (WP_c), and partial factor productivity of N (PFP_N) across two maize growing seasons (2023–2024). Results showed that increased N rate at WTD of 2 m caused soil nutrient loss, while at a WTD of 4 m, it improved soil organic carbon, nitrogen, phosphorus, and potassium. Maize yields decreased with deeper WTD and lower N rate, with WTD contributing more to yield variation than N rate (16 % vs. 10 %). Grain number had a stronger effect on yield than kernel weight (0.65 vs. 0.40), with the former mainly influenced by WTD and the latter by N rate. Deeper WTD reduced ET_c by 68 mm, groundwater evaporation by 73 mm, and the contribution of groundwater to ET_c by 11 %. WP_c did not differ significantly among treatments, suggesting a linear yield–ET_c relationship. Both lower WTD and N rate increased PFP_N, with WTD affecting N utilization efficiency and N rate influencing N uptake efficiency. This study offers practical insights into water–fertilizer managements under fluctuating groundwater conditions to support sustainable maize production.