Synergistic Phosphorus Management: Controlled-Release Fertilizer with Dual Activation Function

Efficient phosphorus (P) management in agriculture faces two critical challenges: minimizing soil P fixation and unlocking the potential of legacy soil P. While these issues have been addressed separately, their combined effect remains unexplored, and truly multifunctional P fertilizers are scarce. This study bridges this gap by developing an innovative controlled-release P fertilizer that synergistically tackles both challenges. A fertilizer was engineered by integrating nanohumic acid (HA) as a P activator within a biobased polyurethane (PU) coating, creating a dual-action system for P delivery and soil activation. Through an optimized activation process combining steam explosion and ball milling, weathered coal was transformed into high-performance HA. Fractionation yielded three HA variants, with lower molecular weight fractions exhibiting enhanced oxygen content and active functional groups. The 10 kDa fraction (HA10) emerged as the optimal PU film modifier, significantly enhancing the coating’s barrier properties and P release kinetics. Our HA-modified fertilizers demonstrated remarkable longevity (34–60 days), extending P release by 19–45 days compared to conventional coatings. In soil incubation studies, the HA10-modified fertilizer (CF-10) maintained consistently elevated Olsen P levels (approaching 32 ppm at the age of 60 days of cultivation) over 60 days, outperforming traditional formulations. This sustained P availability stems from the synergy between controlled nutrient release and HA-mediated soil P activation within localized microdomains. This study not only introduces a fertilizer technology but also provides crucial insights into the interplay between controlled P release and soil P activation. Our findings offer a blueprint for developing next-generation P fertilizers that promise to revolutionize nutrient management in agriculture, addressing both immediate crop needs and long-term soil fertility.