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Background and aims: Potassium (K), Calcium (Ca), and magnesium (Mg) are essential nutrients for plant and animal growth. The ratio of K/(Ca + Mg) in forage is considered as an indicator of grass tetany. While atmospheric nitrogen (N) deposition is declining or projected to decline in many countries, it remains unknown whether historical N inputs would have legacy effects on K, Ca, and Mg nutrition in soil and plants. Methods: After the cessation of 6-yr N addition with wide-ranging rates, we measured the concentrations of K, Ca, and Mg in soil and plants in a temperate steppe of northern China during three successive years from 2016 to 2018. Results: Soil K/(Ca + Mg) ratios were increased by historical N addition across the three years. Soil K/(Ca + Mg) ratios were higher than 0.08, indicating potential occurrence of grass tetany for ruminants. Plant mineral concentrations and K/(Ca + Mg) ratios at the plant community level showed no variation with increasing historical N addition rates in all the three years, except for the increasing K and Ca concentrations in 2017. All plant functional types showed strong stoichiometric homeostasis with respect to nutrient concentrations, which contributed to the stable forage K/(Ca + Mg) ratio under the N-induced increasing soil K/(Ca + Mg) ratio. Conclusion: Our results highlight the critical role of stoichiometric homeostasis in maintaining forage non-N mineral nutrition of natural grasslands under the background of soil nutritional alterations. [ABSTRACT FROM AUTHOR]