Valorization of sugar industry waste into pelletized soil amendments for enhanced plant growth and soil improvement

• Six pellet formulas (F) were made from sugar industry residues. • F2 showed enriched NPK content and an optimal C/N ratio, confirming compost maturity. • F2 exhibited favorable bulk density, wettability, durability, and pellet formation compared with other formulations. • F2 improved soil WHC (42.56 %) and early-stage NPK availability. • F2 increased chili biomass by 31.2 % and shoot height by 27.5 %. Overreliance on synthetic fertilizers in high-input agriculture has led to soil degradation and environmental pollution, necessitating sustainable alternatives. This study developed pelletized organic soil amendments from sugar industry residues, vinasse sludge, molasses wastewater, and bio-organic compost and assessed their physicochemical properties and agronomic performance. Six formulations were produced through aerobic fermentation in ventilated containers and pelletized under controlled moisture and particle size. Among them, F2 (sludge + vinasse sludge + molasses wastewater) exhibited superior characteristics, including high organic matter (43.06 mg kg⁻ 1 ), total nitrogen (2.07 mg kg⁻ 1 ), phosphorus (0.61 mg kg⁻ 1 ), potassium (1.88 mg kg⁻ 1 ), bulk density (714.60 kg m⁻³), and wettability index (45.79 %), significantly outperforming other formulations ( p ≤ 0.05). To further evaluate nutrient dynamics, the formulations were combined with sand (sand + F1 - F6). SF2 showed the highest early availability of N, P, and K compared with other treatments. Greenhouse trials with Capsicum annuum L. showed that plants treated with F2 (ChF2) significantly enhanced shoot height, biomass, and chlorophyll content. ChF2 achieved 27.5 % greater shoot height and 31.2 % more biomass than the control. Soil amended with F2 also demonstrated improved water retention and nutrient availability during early growth stages. The pelletized format provided practical advantages, such as ease of handling, controlled nutrient release, and compatibility with mechanized application. These findings indicate that F2 is an effective organic alternative to synthetic fertilizers, contributing to improved soil fertility and sustainable nutrient cycling. Further research should explore long-term field performance, microbial interactions, and economic feasibility to support large-scale adoption.