Chemical Fractions of Soil Organic Matter and Their Interactions with Cu, Zn and Mn in Vineyards in Southern Brazil

This study aimed to evaluate the impact of vineyard cultivation time and the use of metal-based fungicides on the chemical fractions of soil organic matter (SOM), as well as their interactions with Cu, Zn, and Mn in vineyard soils from Southern Brazil with varying histories of fungicide application. Soil samples were collected from vineyards aged 35, 37, and 39 years in the Serra Gaúcha region, and 13, 19, and 36 years in the Campanha Gaúcha. In each region, samples were also collected from a non-anthropized reference area. In the oldest vineyards, sampling was conducted both within and between the planting rows. From the collected soil samples, chemical fractionation of SOM was performed, yielding the following fractions: non-humic substances (nHS), particulate organic matter (POM), fulvic acid (FA), humic acid (HA), and humin (Hu). After this step, Fourier-transform infrared (FTIR) spectra were obtained for the humic acids, from which the aromaticity index (AI) and relative intensities (RI) were calculated. In each SOM fraction, total organic carbon and the concentrations of Cu, Zn, and Mn were determined. Changes in land use influenced the distribution and chemical nature of SOC and its interaction with metals. HA from vineyard soils showed greater humification and aromaticity, while Cu was mainly associated with HA and FA, and Zn and Mn accumulated in the Hu. Over time, vineyard cultivation, especially with cover crop management, contributed to increased SOC stocks, reaching levels comparable to those in native areas.