Long-term straw return is a key practice for enhancing soil fertility in the North China Plain. However, existing research has largely focused on nitrogen substitution, overlooking the risks of potassium (K) accumulation and the suitability of current farmer K application rates. This study evaluated a 14-year field experiment (2011–2023) assessing straw return rates (full, half, none) and nitrogen reduction levels (0%, 15%, 30%) on maize yield, soil physicochemical properties, and potassium balance. Results indicated that full straw return with 15% nitrogen reduction (S-15%N) or half straw return with conventional nitrogen (1/2SN) achieved the highest yields, increasing production by 7.3–9.2% compared to the control. This indicates that the 1/2SN and S-15%N treatments are a viable and efficient alternative that delivers agronomic benefits comparable to full-rate incorporation while optimizing resource utilization. The potassium nutrient index for all straw-return treatments was significantly greater than “1”, and the soil apparent potassium balance was highly positive. Even without straw, the current application rate of 150 kg K 2 O·ha -1 is sufficient to maintain a potassium surplus. With straw return, this redundant potassium input leads to excessive soil accumulation, suggesting a need to re-evaluate the fertilization rate to improve nutrient use efficiency. Structural equation modeling suggested that straw incorporation is primarily associated with improved crop utilization of soil background potassium, mediated through the enhancement of aggregates >2 mm and reduced bulk density, rather than relying solely on chemical potassium fertilizers. In summary, the current management model of the “nitrogen-straw coupling system” in the North China Plain still requires further optimization, and there is also potential for reducing potassium fertilizer application. For fields where crop residues are routinely incorporated into the soil, we recommend moderately reducing potassium fertilizer application based on nutrient balance, while implementing either “partial incorporation” or a “15% reduction in nitrogen” to maximize utilization efficiency.
LI et al. (Mon,) studied this question.