Effect of Different Potassium Fertilizer Application Rates on the Yield and Potassium Utilization Efficiency of Maize in Xinjiang, China

Potassium (K) is crucial for global maize (Zea mays L.) production, yet the issue of “high K fertilizer input but low utilization efficiency” in K-rich soils of Xinjiang remains underexplored. A three-year field experiment (2020, 2021, 2024) in Xinjiang evaluated the effects of reduced K application on maize growth, grain yield (GY), and K-use efficiency. Five treatments were tested: K100 (136.0 kg K2O·ha−1), K60 (83.5 kg K2O·ha−1), K40 (55.6 kg K2O·ha−1), K0 (no K), and CK (no fertilizer). The research shows that K60 significantly outperforms K100 in terms of physiological parameters (plant height + 2.7–34.7%, leaf area index (LAI) + 6.3–26.8%, dry matter + 22.0–28.8%); GY and thousand kernel weight (TKW) improved by 6.9–15.1% and 9.3–30.3%, respectively. The potassium fertilizer productivity (PFPK) and potassium fertilizer agronomic efficiency (AEK) increased by 78–112.3% and 176.4–2085% compared to the K100. During the three-year period, the maximum net income of K60 reached 28,206 CNY·ha−1, which was 18.9–20.7% higher than that of K100. Regression analysis identified an optimal K rate of 82.2–85 kg·ha−1 for maximum yield. Least squares structural equation mode (PLS-SEM) and correlation analyses revealed that moderate K reduction enhanced vegetative growth and optimized yield structure, indirectly boosting yield, thereby directly driving net income. Thus, reducing K input can achieve “lower input with higher efficiency”, offering a practical basis for optimizing K management in arid-region maize systems.