Effects of Compound Fertilizer Containing Polyhalite on Soil and Maize Growth Under Different Nitrogen Levels

The growing potassium (K) demand and supply–demand imbalance in intensive agriculture require the development of multi-nutrient K fertilizers. Polyhalite (POLY), a multi-nutrient natural mineral rich in K, calcium, magnesium, and sulfur, can enhance soil nutrient diversity and fertility. However, research on its synergistic application with nitrogen (N) fertilizer remains limited. Therefore, this study was designed to apply three different fertilizer composites at four N concentration gradients through field plot experiments to evaluate crop productivity and nutrient use efficiency. Results revealed that the application of both compound fertilizers with N fertilizer increased maize yield, ranging from 1.03% to 11.53%, compared with the PK control. Moreover, 25-7-8 (MOP)(POLY26%) achieved a maximum yield of 9499.88 kg/ha at the N1 (170 kg/ha) level. This represents a significant increase of 11.53% compared with the PK control. Moreover, the application of compound fertilizer containing POLY could significantly increase the N fertilizer utilization rate; improve the quality of maize; and exert a significant effect on soil pH, EC, and nutrient content. This study paves the way for broader application of POLY by establishing its novel role as a sustainable nutrient source. It provides critical strategic guidance for advancing global resource-efficient agriculture.