Cotton/mung bean intercropping improves crop productivity, water use efficiency, nitrogen uptake, and economic benefits in the arid area of Northwest China

•The study proposed a new cotton/mung bean intercropping (CMBI) system based on the traditional monocropping cotton (MC).•The CMBI system showed higher crop yield, water use efficiency (WUE) and nitrogen use efficiency than the MC.•The CMBI system produced economic benefits much better than the MC system.•390 kg ha−1 in CMBI system was recommended as an appropriate nitrogen application rate to improve WUE and economic benefits. It is still a long-term challenge to improve crop production and economic benefits in arid area of northwest China. The objective of this study was therefore to propose a new and promising cotton/mung bean intercropping (CMBI) system to cope with the challenge based on the traditional monocropping cotton (MC) system. A two-year field experiment was conducted to evaluate crop production and economic benefits between the CMBI and MC systems by analyzing the total land output (TLO), aboveground dry matter, nitrogen uptake, water use efficiency (WUE), nitrogen use efficiency (NUE), partial factor productivity (PFP) of nitrogen, and economic benefits. Experiment treatments consisted of two cropping systems (MC and CMBI systems) and a combination of the CMBI system with different N-fertilizer rates [160 (N160), 315 (N315), 390 (N390), and 475 (N475) kg ha−1 in 2016, and 160 (N160), 315 (N315), and 390 (N390) kg ha−1 in 2017], respectively. All treatments were designed using a randomized complete block with three replications. The results indicated that no significant differences in growth parameters [PH (plant height), SD (stem diameter), and LAI (leaf area index)] of cotton were found between the MC and CMBI systems in 2016 and 2017. Compared with the MC system, however, the CMBI system significantly increased TLO, aboveground dry matter, total N uptake, WUE, NUE, PFP for nitrogen, and economic benefits in 2016 and 2017. The result suggested the CMBI system had greater production advantages and economic benefits than the MC system. In addition, compared to the N160 treatment, other N treatments (N315, N390, and N475) in the CMBI system significantly enhanced crop growth, TLO, total aboveground dry matter, total N uptake, WUE, and economic benefits. However, PFP for nitrogen and NUE significantly decreased with the increase of application N rates. According to analyzing the production functions of different application N treatments, we found that 390 kg ha−1 in the CMBI system might be recommended as an appropriate application N rate to i