Decoupling Dynamics, Utilization Efficiency, and Driving Mechanisms of Potash Fertilizer Inputs and Grain Production in China: Evidence from Provincial Panel Data, 2000–2024

Potassium is an essential nutrient for crop growth and plays a critical role in regulating water metabolism, facilitating photosynthate transport, and improving agricultural product quality. The precise management of potash fertilizer inputs is therefore vital for enhancing agricultural productivity and promoting sustainable resource use. Using panel data for 31 provinces in China from 2000 to 2024, obtained from the China Statistical Yearbook, this study integrates the Tapio decoupling model, stochastic frontier analysis (SFA), fixed-effects models, and an XGBoost–BiLSTM hybrid model to investigate the dynamic relationship, utilization efficiency, and driving mechanisms of potash fertilizer inputs and grain production. The results indicate that the relationship between potash fertilizer inputs and grain production has shifted from an expansive negative decoupling state—characterized by faster growth in fertilizer inputs than in output—to a strong decoupling state, where fertilizer inputs decline while grain production continues to increase. This transition exhibits a clear spatial gradient, with improvements from eastern to northeastern and central regions. Potassium use efficiency (KUE) shows a steady upward trend, with significant regional heterogeneity, characterized by higher efficiency in the south, lower efficiency in the north, and notable differentiation in western regions, largely driven by climatic and soil variations. Despite these improvements, substantial potential for reducing fertilizer inputs remains across provinces. Potash fertilizer inputs exert a significant positive effect on grain production, while the cultivation of potassium-intensive crops, such as sugar crops, tobacco, and fruits, is a key driver of regional demand. Model projections suggest that from 2025 to 2030, grain production will grow at an annual rate of 1.2–1.5%, while potash fertilizer inputs will decline by 2–4% annually, indicating a transition toward greener agricultural development. These findings highlight the need for region-specific fertilization strategies, optimized fertilizer structures, and improved soil nutrient monitoring systems to ensure food security and sustainability.