Objectives Suitable density and nitrogen fertilizer management are important measures to improve maize lodging resistance, ensure high and stable yield and improve production efficiency. The objective of this experiment is to study the influence of nitrogen application rate, planting density and their interaction on maize yield, lodging resistance.

Methods Field experiments were conducted in Jinzhong City, Shanxi Province in 2018 and 2019, using maize cultivar ‘Zhengdan 958’ as the test materials. Four N application rates 0, 120, 180 and 240 kg/hm² (denoted as N0, N1, N2, and N3), three planting densities 60000, 75000 and 90000 plants/hm² (denoted as D1, D2, D3) were setup. The agronomic traits of stalk at silking stage, the length-to-thickness ratio, mechanical traits, and lodging rates of stalks below the ears were investigated at physiologically maturing stage, and the yields were recorded at harvest of spring maize.

Results The maize yield showed a trend of first increasing and then decreasing with the increase of planting density and nitrogen application rate. The average yield under D2 of two years was 13792 kg/hm², which was 4.8% and 8.3% higher than that under D1 and D3, respectively. Compared with N0, N1, N2, and N3 increased yields by 24.3%, 26.7%, and 23.9%, respectively. N3 was recorded lower yield than N1 and N2, although N3 did not impact the kernel number per ear and 1000-grain weight significantly. With the increase of planting density, the stem diameter was significantly decreased, but the plant height, ear height, the length-to-thickness ratio of the third to sixth internode above ground were increased, and the rind penetration strength, bending strength, crushing strength became worse. D2 and D3 were recorded 1.33 and 3.73 percentage point higher than D1 in the two-year average lodge rate, and N1, N2, and N3 were recorded 2.50, 3.25, and 4.80 percentage point higher than N0. Proper increasing of N rate offset the deterioration of stalk biological and mechanical properties which were caused by increased planting densities. Under D2 and D3, the third to sixth above ground internodes in N2 treatment remained similar or even higher rind penetration, bending, and crushing strength, while N3 decreased the mechanical properties, relative to D1.

Conclusions Reasonable nitrogen application rate can prevent the stalk thinning caused by the increased planting density, improve the mechanical properties of maize stalks, reduce the lodging risk, and increase yield at last. In the central area of Shanxi Province, planting density 75000 plants/hm² and nitrogen application rate 180 kg/hm² appear the optimum combination in consideration of maize yield, stalk mechanical properties and lodge resistance comprehensively.