<p>Agricultural ecosystems play a significant role in global food security and climate mitigation through crop production and soil organic carbon sequestration. It is well-established that potassium fertilization enhances crop yield in potassium-deficient regions; however, the factors driving crop yield responses to potassium remain insufficiently characterized at a large scale. Moreover, despite the significant roles of soil organic carbon in soil health and global carbon cycling, the effect of potassium on soil organic carbon in croplands has been less studied. Herein, we collect data from 1185 observations in agricultural ecosystems to conduct a meta-analysis study. We find that potassium fertilization increases cereal yield and soil organic carbon by 19.3% and 4.4%, respectively. Mean annual precipitation and experimental duration are the most important factors affecting potassium effects on cereal yield and soil organic carbon, respectively. Specifically, potassium effects on cereal yield increase with mean annual precipitation, and the potassium-induced increase in soil organic carbon is significant only after long-term (&gt; 20 years) potassium fertilization. Our findings suggest that, in addition to nitrogen and phosphorus, potassium is also crucial for not only cereal yield but also soil carbon sequestration, which should be fully valued in future soil nutrient management, especially in potassium-deficient regions.</p>