Smart fertilizer: Ameliorant-based NPK coating enhanced rice yield and quality in vertisol paddy soil

Abstract Inorganic fertilizers, which provide nutrients, such as nitrogen (N), phosphorus (P), and potassium (K), are recognized for their rapid-release properties; therefore, the future of rice cultivation will require the development of smart fertilizers (SF). This study focused on creating an NPK-coated fertilizer using ameliorant materials to slow nutrient release and improve rice growth, yield, and Relative Agronomic Efficiency (RAE) in vertisol paddy fields. The research involved soil analysis, fertilizer formulation, and N release tests. Field tests at two locations included 12 treatments, with eight NPK-coated formulas and four controls, each replicated thrice. Fertilizer was applied once before planting or each planting cycle. Observations covered soil properties, NO 3 - and NH 4 + release, agronomic parameters, RAE, and grain nutrient content. Results showed that NPK-coated fertilizers released nutrients more slowly than inorganic ones. Four formulas, T4, T5, T6, and T8, were suitable for the further development, demonstrating RAE values exceeding 104%. These formulas balance N, P, K, and zinc (Zn), meeting the nutritional needs of rice. Hazardous heavy metals were not detected. NPK-coated fertilizers were more efficient, requiring lower doses, while achieving rice yields of 6–8 t ha-1. Based on the study's results, we conclude that NPK-coated fertilizers are effective and environmentally sustainable, improving rice productivity in vertisol paddy fields. The implication of NPK-coated formulation using natural coating materials is a slow-release fertilizer (SRF) with potential in the agricultural sector as an alternative fertilizer for future rice crop.