A mini review of modified lignite-based slow-release fertilizer coated by polymer

Slow-release fertilizers (SRFs) offer a sustainable solution to improve nutrient efficiency and reduce environmental losses. This review focuses on lignite, a low-rank coal with high porosity, as a carrier for SRFs. When combined with biodegradable polymers like polyvinyl alcohol (PVA), lignite-based SRFs exhibit enhanced nutrient retention and controlled release. Biochar–PVA composites retained over 80% nitrogen after 30 days, while paraffin–lignosulfonate coatings reduced nitrogen release to 28% in 24 hours. CTAB-templated mesoporous silica extended nutrient release up to 45 days and retained 85% nitrogen. Field studies showed 72% less ammonia volatilization and 32% higher maize yields using biochar–polymer matrices. PVA also provides water retention up to 7.5 g/g with a release period of 18–30 days. This novelty departs from conventional polymer- based SRFs by integrating low-rank coal with inherent humic substances, CTAB for controlled pore structure, and PVA as an affordable crosslinker, resulting in improved nutrient release efficiency and positioning lignite– polymer SRFs as a sustainable, eco-friendly solution for modern agriculture.