Vinasse fertigation modifies soil-microbiota-plant interactions and metabolism in sugarcane

Vinasse fertigation is widely used in sugarcane systems to recycle nutrients and organic residues, yet its effects on soil-microbiota-plant interactions under field conditions remain insufficiently understood. This study evaluated the effects of localized vinasse application on soil physicochemical properties, microbial communities, and leaf metabolism of sugarcane, combining conventional soil analyses with ¹H NMR-based metabolomics and assessment of crop development and post-harvest quality. Vinasse application increased soil pH (6.26-6.73) compared to the control (5.33-5.88) and enhanced base cations, particularly K⁺ (up to 5.54 mmol dm^-3 versus 1.46 mmol dm^-3), while electrical conductivity varied over time, with higher values at 90 and 360 days after application (p < 0.05). Microbial populations responded dynamically, with differences in phosphorus- and potassium-solubilizing bacteria and nitrogen-fixing bacteria depending on sampling time (p < 0.05). At the plant level, after 90 days, vinasse-treated samples showed higher relative contributions of carbohydrates, whereas control plants showed higher levels of organic acids and amino acids. Despite this pattern, aconitic acid showed higher relative abundance under vinasse across sampling times, indicating shifts in central carbon metabolism. These responses were associated with increased vegetative growth and yield, with tonnes of cane per hectare reaching 101.69 compared to 77.03 in the control. However, vinasse reduced technological quality, with lower sucrose (16.06 vs 20.60 %w v^-1), °Brix (18.07 vs 23.20%), and total reducing sugars (25.73 vs 42.31 %w v^-1), alongside higher glucose and fructose (p < 0.05). Overall, vinasse application shifts carbon allocation toward growth rather than sucrose accumulation, highlighting a trade-off between productivity and industrial quality and the need to optimize application strategies.