Engineering Organomineral Composting Using Sugarcane Residues: Effects of Phosphate Sources and Phosphate-Solubilizing Bacteria on Nutrient Dynamics

The formulation of organomineral composts can be used to modulate nutrient dynamics and improve the quality of fertilizers produced from agro-industrial residues. This study evaluated the effects of compost formulation, phosphorus source, and inoculation with phosphate-solubilizing bacteria on nutrient dynamics during the composting of sugarcane filter cake. Six formulations combining filter cake, poultry litter, and agricultural gypsum were evaluated: organic compost (T1); compost enriched with reactive phosphate rock (T2); reactive phosphate rock + phosphate-solubilizing bacteria (T3); triple superphosphate (T4); triple superphosphate with a modified filter cake-to-poultry litter ratio (T5); and compost without gypsum (T6). The experiment was conducted in a completely randomized design with five replicates, and composts were evaluated at 45, 65, and 115 days. Data were subjected to analysis of variance considering formulation, composting time, and their interaction. A significant interaction between compost formulation and composting time was observed for organic matter, organic carbon, P, K, Ca, Mg, and pH, whereas N and S were independently affected by these factors. Organic matter and organic carbon contents decreased by 18% and 19%, respectively, at 115 days compared with the earlier composting periods. P-enriched formulations had 52% higher P content than non-enriched composts, while T2 and T5 showed comparable P content. Inoculation with phosphate-solubilizing bacteria temporarily increased P content during the composting phase, whereas gypsum did not improve N conservation. These findings demonstrate that formulating composts with reactive phosphate rock is a technically feasible strategy for producing P-enriched organomineral fertilizers while promoting nutrient recycling and the valorization of agro-industrial residues.