Sulfur (S) has a vital agronomic role in vegetable development, yet it is often the most neglected macronutrient in current agronomic practices and agrochemical research. Over the past decades, sulfur deficiency in soils has become increasingly common worldwide, harming the quality of crops as well as their yields. Elemental sulfur (S8) stands out among other sulfur-based fertilizers as the most concentrated source (~100%). Additionally, S8 is not susceptible to leaching problems like sulfate fertilizers, and it is an abundant byproduct of petrochemical industry. Nevertheless, plant uptake is only possible after S8 biological oxidation by soil microorganisms, a slow rate process strongly influenced by the fertilizer characteristics. Oxidation is, therefore, the most limiting factor for S8 agronomic efficiency, with commercial pellets generally taking more than 3 years for a conversion of only 50% of the applied products. Considering the intense world population growth expected for the next decades, developing innovative strategies to enhance fertilizers efficacy is fundamental to meet future food demands in a sustainable way.
In the present work, we propose a novel S-fertilizer based on the chemical modification of S8 cyclic structure into a linear amorphous form, more available to oxidizing microorganisms, as an approach to improve the oxidation rate. In order to design this type of material, we applied the recently developed inverse vulcanization technique, a simple copolymerization method that guarantees better processing control for sulfur and allows the formation of functional sulfur-rich polymers. In addition, this technique involves some green chemistry principles, such as the lack of solvent use and excellent atom economy. Soybean oil was selected as comonomer for the reaction as a cheap, non-toxic and renewable feedstock. The S-oxidation achieved by the polysulfide products revealed to be more than 50% superior than S8, and the soybean oil fraction of those materials displayed a role as carbon source for microorganism activity. Therefore, the results could support the sustainable development of a non-conventional S-fertilizer with enhanced efficiency and multifunctional properties.