Objectives The suitable plant density and nitrogen application rate were studied for efficient spring maize production and nitrogen and water use efficiencies under the technique of whole plastic-film mulching and double-furrow sowing in rain-fed cropland area.

Methods The field experiment was conducted in the Northwest Loess Plateau Observation Station of Crop Production of Ministry of Agriculture, Dingxi City, Gansu Province, where is typical rain-fed area with one crop a year. The field experiment was carried out in 2016 and 2017 with a density-tolerant cultivar of maize ‘Xianyu335’ as tested material. Three plant densities of 45000, 60000 and 75000 plant/hm², and four nitrogen application rates of 0, 138, 207 and 276 kg/hm² were designed (expressed as N0, N138, N207, N276, respectively). The yield, nitrogen and water use efficiencies of spring maize were investigated.

Results Both the plant density and nitrogen application rate had significant effects on yield, nitrogen and water use efficiencies of spring maize, and the interaction between them was significant as well．Compared to low plant density (45000 plant/hm²) and high plant density (75000 plant/hm²), the grain yields under plant density of 60000 plant/hm² were significantly increased by 24.86%−26.91% and 25.83%−34.34%, respectively. The nitrogen use efficiencies were significantly increased by 41.07% and 41.63%, and the water use efficiencies were significantly increased by 9.87%−18.09% and 17.81%−32.89%. When the nitrogen application rate was increased from 138 to 276 kg/hm², the grain yields and water use efficiencies of maize were significantly increased and all were significantly higher than that of the N0 treatment. Both the grain yields and water use efficiencies were in order of N276 > N207 > N138 > N0, and the maize yields and water use efficiencies in the N276 and N207 treatments were significantly higher than in the N138 and N0 treatments, and there was no significant change between the N276 and N207 treatments. The nitrogen use efficiency of maize was firstly increased with nitrogen application rate and decreased when continue to increase amount of nitrogen fertilizer. With the increasing of nitrogen application rate, the nitrogen partial factor productivity was decreased, and the nitrogen use efficiency reached the highest in N207, which was 4.23% and 27.37% higher than those in N276 and N138 treatments. The increase of maize yield caused synergistic improvement of nitrogen utilization rate and water use efficiency.

Conclusions Under this experimental field condition, comprehensively considering the nitrogen fertilizer and water use efficiency, the appropriate plant density is 60000 plant/hm² and the nitrogen application rate is 207 kg/hm².