Abstract: [Objective] To investigate the response of soil chemical characteristics to various grass-crop rotation combinations. [Methods] In accordance with the crop planting practices in the study area, six crops were selected as research subjects: three economic crops （corn, sunflower, and potato) and three forage crops （alfalfa, millet straw, and sorghum-sudan grass）. Five rotation combinations were established as follows: T1 （alfalfa - sunflower - sunflower - potato - corn）; T2 （millet straw - potato - millet straw - millet straw - sunflower）; T3 （alfalfa - alfalfa - potato - corn - sunflower）; T4 （sorghum-sudan grass - potato - corn - sunflower - corn); and T5 （potato - millet straw - sunflower - potato - millet straw）. Field experiments were conducted over a five-year period in Darhan Muminggan United Banner, Baotou City, Inner Mongolia Autonomous Region. The primary chemical properties of soil at depths of 0-10 cm, 10-20 cm, and 20-30 cm were compared and analyzed under different rotation regimes.[Results] In the 0 - 10 cm soil layer, the T4 combination exhibited significantly higher （P<0.05） levels of total nitrogen, available potassium, inorganic carbon, and total sulfur compared to other combinations. The organic carbon content was highest in the T3 combination and significantly higher （P<0.05） than in the T2, T4, and T5 combinations. Additionally, the carbon-to-phosphorus ratio in the T3 combination was significantly higher （P<0.05） than in other combinations. In the 10 - 20 cm soil layer, the T4 combination showed significantly higher （P<0.05） levels of total nitrogen, available potassium, and total sulfur relative to other combinations. The T3 combination had significantly higher （P<0.05） levels of organic carbon, carbon-to-nitrogen ratio, and carbon-to-phosphorus ratio compared to other combinations. In the 20 - 30 cm soil layer, the T4 combination demonstrated significantly higher （P<0.05） levels of available potassium and total sulfur compared to other combinations. The inorganic carbon content was highest in the T3 combination and significantly higher （P<0.05） than in the T2 combination. Furthermore, the carbon-to-phosphorus ratio in the T3 combination was the highest and significantly higher （P<0.05） than in the T1, T2, and T5 combinations. [Conclusion] Based on the enhanced soil nutrient content from various rotation combinations and the improved efficiency of crop absorption and utilization of these nutrients, it is recommended to adopt the alfalfa-alfalfa-potato-corn-sunflower （T3 combination） as the optimal grass-crop rotation combination for this region. These findings provide a valuable reference for optimizing the grass-crop rotation systems and enhancing the sustainable use of soil resources.

Key words: grass-crop rotation, crop rotation combination, soil nutrients, chemical characteristics