Soil fertilization potential and nutrient dynamics of organic fertilizers derived from sugarcane residues under techno-economic and environmental assessment

Abstract

This study investigates the nutrient dynamics and soil fertilization potential of organic fertilizers produced from sugarcane industry residues. Vinasse was treated through ultrafiltration (UF) and reverse osmosis (RO) to concentrate on macronutrients. The concentrates were then incorporated into filter cake during granulation, generating two types of fertilizers: (i) UF-based and (ii) RO-based formulations. Nutrient enrichment enabled a 2.9- to 11.8-fold reduction in application mass per hectare compared to raw residues. Although sodium was also concentrated, the sodium adsorption ratio remained below thresholds for wastewater reuse in agriculture (<3 meq/L). Nutrient release kinetics revealed that nitrogen was the most readily available nutrient (k = 2.52–3.61 d⁻¹), with delayed release of potassium, phosphorus, and sodium. Column leaching tests further revealed greater retardation factors for granular fertilizers (R: 3.1–32.4) when compared with the liquid concentrates obtained from UF and RO processes, confirming reduced mobility and enhanced nutrient retention. The soil solution analyses confirmed nutrient accumulation in the upper layers (0–10 cm), indicating a low leaching risk and greater plant availability. Earthworm avoidance tests indicated no toxicity, even in RO-based fertilizers, while high filter cake doses alone trigger complete avoidance. In all scenarios analyzed, RO and UF-based fertilizers presented a lower potential for N₂O and CO₂ emission when compared to the commercial mineral fertilizers. Finally, economic analysis showed that the granular fertilizers are cost-competitive (fertilization costs: US$8.5–12.1/ha), especially when considering application logistics. Comparing the fertilizers, ROc-based demonstrated better nutritional performance with higher nutritional concentrations and immediate response to plant needs. UFc-based fertilizers, on the other hand, stood out for their high concentration of organic matter, with widespread use in soil improvement. Overall, the results demonstrate the technical, environmental, and economic feasibility of converting agro-industrial residues into safe and effective fertilizers. Furthermore, the work stands out in identifying pathways toward a more resilient, safe, and low-environmental-impact agriculture.