A soybean polypeptide liquid produced from soybean protein by enzymatic hydrolysis with food-grade proteases, rich in small-molecule peptides and free amino acids with a concentrated molecular weight distribution and high bioavailability. Fully water-soluble and residue-free, it is chloride-free and highly compatible with concentrated macronutrient fertilisers. It can serve as the polypeptide base for amino acid water-soluble fertilisers, organic water-soluble fertilisers and biostimulant products, as a nitrogen source for fermentation media, or as a liquid feed additive. The mild enzymatic process preserves the functional peptide fractions of soy protein, giving stable performance and consistent batches; solid content and pH can be adjusted on request.