Abstract: To clarify the effects of the application ratio of nitrogen/potassium fertilizers on lodging resistance of maize stem and grain yield, a field experiment with split plot design was carried out in western Songnen Plain. The application level of nitrogen fertilizer was used as main factor, while that of potassium fertilizer was used as subsidiary factor. We measured the morphological and mechanical characteristics of maize stem at grain filling stage and grain yield under different combinations of nitrogen and potassium fertilizers (N: 195, 210, 225, 240 kg·hm^-2; K₂O: 70, 85, 100, 115 kg·hm^-2). The results showed that plant height was significantly affected by nitrogen application and the height of gravity center was significantly affected by the potassium fertilization. There were no significant interactive effects of nitrogen and potassium fertilization on plant height, ear height and height of gravity center. Nitrogen and potassium fertilization and their interactions had significant effects on internode length, stem diameter, area of cross section, internode plumpness, breaking resistance, puncture strength, section modulus, stem type index, bending moment, breaking moment, and bending stress. Among all the treatments, the lodging resistance index was the highest under 210 kg N·hm^-2 + 85 kg K₂O·hm^-2 treatment, followed by 225 kg N·hm^-2 + 100 kg K₂O·hm^-2 treatment, and 210 kg N·hm^-2 + 100 kg K₂O·hm^-2 treatment, which were 31.59%-80.86% higher than that of other treatments. Nitrogen and potassium fertilization had significant interactive effect on lodging resistance of maize (F_N×K=19.577^**). According to the morphological and mechanical characteristics of maize stem and grain yield levels, the optimum nitrogen and potassium application scheme for maize lodging resistance was 210-225 kg N·hm^-2 + 85-100 kg K₂O·hm^-2, with a nitrogen/potassium ratio of 1.75-1.88 : 0.71-0.83. Our results provide scientific basis and technical approach for the nutrient efficiency management of high yield, good quality and multiresistance maize population under close planting cultivation in Songnen Plain.

Key words: soil carbon content, global warming impact., land-use conversion, CO₂, CH₄