11 years of controlled-release potassium fertilization reshaped maize ecosystems and drove sustainable soil quality: insights from physical-chemical-biological interactions.

Excessive use of conventional potassium chloride (KCl) fertilizer has led to soil degradation problems such as compaction and salinization. While controlled-release potassium chloride (CRK) fertilizer has the potential to enhance crop productivity and mitigate these problems, its impact on soil quality (SQ) remains unclear. In this study, four potassium (K) fertilization treatments were established: no K application (CK), conventional KCl fertilizer (CRK0), 50 % substitution with CRK (CRK0.5), and full substitution with CRK (CRK1), to assess their effects on the soil quality index (SQI) and maize yield over an 11-year period (2014-2024). Results indicated that maize yields followed a bell-shaped trend, initially increasing and then declining, with the highest yield recorded under the CRK0.5 treatment. Compared to CRK0, CRK fertilizer substitution significantly improved key soil quality components: soil water-holding capacity (81.86 %-166.36 %), enzyme activity (22.48 %-33.63 %), acid-base balance (30.17 %-44.9 %) and organic carbon pool (34.73 %-38.06 %). Meanwhile, CRK treatments reduced microbial network complexity, thereby improving microbial environmental adaptability, minimizing microbial energy loss, and enhancing soil carbon and nitrogen sequestration efficiency. Furthermore, the modularity of bacterial and fungal community modules was increased by 12.07 %-31.08 % and 2.63 %-12.5 %, respectively, thereby improving SQ. Structural equation modeling revealed that substituting of CRK fertilizer significantly increased SQI, through enzyme activity, acid-base balance, and modularity, thereby significantly improving maize yield. Compared to CK, the SQI was improved significantly by 12.34 %-155.61 % under long-term K fertilization, and CRK treatments further enhanced SQI by 65.57 %-127.53 % relative to CRK0 treatment. The highest SQI (0.5904) was observed in the CRK1 treatment. Notably, SQI was positively correlated with maize yield (β = 0.508, p < 0.05), and CRK substitution increased yield by 7.45 %-13.78 % over CRK0. These findings underscore the value of rational CRK fertilizer use in improving the productivity of medium-and low-yield croplands, safeguarding food security, and promoting sustainable agricultural development.