Activated-Lignite-Based Super Large Granular Slow-Release Fertilizers Improve Apple Tree Growth: Synthesis, Characterizations, and Laboratory and Field Evaluations

In this work, lignite, a low-grade coal, was modified using the solid-phase activation method with the aid of a Pd/CeO2 nanoparticle catalyst to improve its pore structure and nutrient absorption. Results indicate that the adsorption ability of the activated lignite to NO3–, NH4+, H2PO4–, and K+ was significantly higher than that of raw lignite. The activated lignite was successfully combined with the polymeric slow-release fertilizer, which exhibits typical slow-release behavior, to prepare the super large granular activated lignite slow-release fertilizer (SAF). In addition to the slow-release ability, the SAF showed excellent water-retention capabilities. Soil column leaching experiments further confirmed the slow-release characteristics of the SAF with fertilizer nutrient loss greatly reduced in comparison to traditional and slow-release fertilizers. Furthermore, field tests of the SAF in an orchard showed that the novel SAF was better than other tested fertilizers in improve the growth of young apple...