Hydrophobic Nanostructured Coatings of Colloidal Lignin Particles Reduce Nutrient Leaching and Enhance Wheat Agronomic Performance and Nutritional Quality

Traditional farming practices are increasingly being replaced with more sustainable approaches, including the development of slow-release fertilizers (SRFs), to mitigate environmental stress and ensure food security for the ever-growing global population. Despite the rising focus on eco-friendly materials like biopolymers for fertilizer coatings, optimizing their hydrophobicity remains a significant challenge. In this context, nanotechnology offers a promising route toward achieving hydrophobicity and sustainability. In this study, hydrophobic colloidal lignin particles (20–50 nm) were synthesized using a straightforward acid precipitation method involving the coprecipitation of lignin (LGe) and sodium dodecyl sulfate (SDS). This strategy aimed to reduce particle size, enhance stability, and increase hydrophobicity by incorporating the nonpolar SDS alkyl chains onto the surface of the nanomicelles. TEM and STEM microscopy confirmed the formation of core–shell hybrid micelles, which were incorporated into a cross-linked carboxymethyl cellulose (CMC) matrix at various ratios to produce a series of waterborne coating formulations and films. The spherical morphology and new surface features, along with their integration into an interpenetrating cross-linked network, led to the formation of nanostructured coating films with good hydrophobicity (WCA ∼ 106.1°) and slow biodegradability in soil. When applied to diammonium phosphate (DAP) granular fertilizer, the coatings revealed good interfacial adhesion, enhanced hardness (2.5-fold), and improved water-holding capacity in soil (18%). Most importantly, a 100 day nutrient leaching study revealed an impressive nutrient-release longevity, showing a 75% reduction in N–P leaching. Subsequently, these SRFs were evaluated in a 6 month wheat ( Triticum aestivum )) cultivation trial across different soil textures, demonstrating substantial enhancements in leaf area (150–200%), total root length (160%), biomass production (575%), grain yield (115–264%), and quality-related parameters. These findings highlight a robust solution for addressing nutrient deficiencies and promoting sustainable agricultural practices, especially for crops with extended growth cycles, while inspiring novel nanostructured coatings for broader applications.