Facile Synthesis a Potential Nitrogen-Enriched Weathered Coal Fertilizer: Excellent Slow-Release Performance and Improving Plant Quality

Based on weathered coal (WC), a new type of nitrogen-enriched weathered coal fertilizer (NCF) was synthesized herein using hydrogen peroxide and urea in a closed container. Inductively coupled plasma mass spectrometry, elemental analysis, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Contact angle, Zeta potential and X-ray diffraction (XRD) measurements were performed; the obtained results showed that NCF has potential slow-release nitrogen properties. Additionally, the FTIR and XPS measurements revealed that NCF has various oxygen-containing active functional groups along with nitrogen-containing groups. A soil leaching test and the release kinetic model fitting of total nitrogen showed that NCF released nitrogen more slowly and over a longer time than urea, with nitrogen still being released after 70 days. Further, a mechanism study was performed, which revealed that NCF has a dual release performance that is similar to that of biochar and “dissolved black nitrogen.” Moreover, the total nitrogen release behavior of NCF was dominated by the multi-effects of the coal carbon carrier, including electrostatic attraction, the unconventional formation of hydrogen bonds, and decomposition of the nitrogen-containing groups. Furthermore, the application of NCF in both soil types (Lou and Loessal soil) stimulated the germination rate of spinach seeds and improved the chloroplast pigment content as well as the nutritional quality of spinach leaves. These results suggest that abandoned weathered coal may be fully utilized in the mining area and that NCF may have promising potential in improving plant quality and sustainable agriculture applications. Graphical Abstract