Multi-objective optimization of water and nitrogen regimes for enhancing crop productivity, economic return and resource use efficiency of drip-fertigated maize-soybean strip intercropping system in northwest China

Optimizing water-fertilizer regime in maize-soybean strip intercropping systems is critical for enhancing crop productivity, profitability and resource use efficiency. A two-year field experiment was conducted under drip fertigation in northwest China, with three irrigation levels (W100:100%ETc, W80: 80%ETc and W60: 60%ETc) and four nitrogen rates (N250: 250 kg N ha−1, N200: 200 kg N ha−1, N150: 150 kg N ha−1 and N0: 0 kg N ha−1 for maize; 60 kg N ha−1 for soybean). Energy yield (EY) was introduced to integrate system productivity, and nitrogen use efficiency (NUEe) and water productivity (WPe) were assessed at the system level. The results showed that nitrogen rate, irrigation level, and their interaction significantly affected crop growth, nitrogen uptake, evapotranspiration, grain yield, EY, economic return, NUEe, and WPe (p < 0.05). The MSN200 + 60W80 achieved the highest grain yield (maize: 17,046.4 kg ha−1, soybean: 3488.9 kg ha−1), EY (35.5 MJ m−2), net income (4297.8 $ ha−1), NUEe (747.8 MJ kg−1), and WPe (591.4 MJ ha−1 mm−1). Compared to MSN250 + 60W100, MSN200 + 60W80 increased energy yield by 11.9%, net income by 28.1%, NUEe by 6.5%, and WPe by 17.3%. The response surface modeling found that the optimal nitrogen rate ranged between 237.3 and 288.1 kg N ha⁻¹ (177.3–228.1 kg ha⁻¹ for maize), with irrigation at 75–90% ETc maximizing system performance. This study optimized water-nitrogen regimes to improve crop productivity and profitability in maize-soybean strip intercropping systems in arid regions.