Fire lead to disturbance on organic carbon under sugarcane cultivation but is recovered by amendment with vinasse.

Sugarcane burning has been widely practiced in Brazil and worldwide. In the long term, this farming practice can cause soil erosion, reduction in organic carbon (OC) and consequently, changes in the structure of soil organic matter (SOM). Such changes may be difficult to reverse. This study aimed to assess the medium- and long-term effects of sugarcane burning on SOM characteristics, both in terms of quantity and structural quality and evaluate the application of vinasse as a strategy to attenuate fire-induced changes in burned soil. The experiment was conducted in a 50-year-old sugarcane field on soils classed as Cambissolo Háplico (Inceptisol). Four plots were sampled: a) burning of sugarcane for harvest for 37 years (SCB37); b) renewal of the sugarcane field and burning for harvest for 3 years (SCB3); c) renewal of the sugarcane field without burning for harvest for 3 years (SCWB), and d) renewal of the sugarcane field and burning for harvest with the application of vinasse for 3 years (SCV). Chemical and physical characterization of SOM was performed by solid-state spectroscopy (UV-vis, ATR-FTIR e C NMR CP/MAS) and chemometric techniques. The results showed that sugarcane burning drastically impacts SOM content and its chemical structure, however, the application of vinasse preserves and restores the soil from the fire effects. Content of soil OC, particulate OC, mineral-associated OC, humic acid, humin and light fraction OM that were affected by fire, had an increase and recovery of contents by the vinasse application. Solid state spectroscopy showed that labile structures were lost in humic acids (HA) by fire and recalcitrant structures were preserved. The application of vinasse incorporated fragments of lipids and carbohydrates in HA structure. Burning sugar cane straw affects the integrity of soil organic matter but can be restored by applying vinasse.