Mechanochemical Activation of Elemental Sulfur Increases Its Bioavailability in the Forage Species Brachiaria Production

Although sulfur is an essential macronutrient for plants, its supply through elemental S-0 is not efficient, demanding its oxidation by soil microbiota before plant uptake. Thus, we demonstrate that a simple reactive mechanochemical route, using anhydrous KOH as a reactant with no need for water addition, can convert S-0 to bio-absorbable oxidized forms, leading to residual K+ as a plant nutrient in the final composition. The powdery products obtained by 1 h (S-1 h) or 8 h (S-8 h) milling have been fully converted to HSO3-, SO32-, and SO42-, also suggesting different amounts of these sulfur oxides according to the milling. S-1 h and S-8 h were efficient for S and K fertilization, as probed by the successful growing of the forage crop Brachiaria ssp. in a greenhouse trial, with similar biomass yields observed for K2SO4 (positive control) and superior to S-0 + KCl (negative control). These data suggest that the mechanochemical process provides a sustainable route to increase sulfur plant bioavailability, suggesting a simple alternative that can be easily implemented in forage plant production sites such as Brachiaria ssp.