Small Peptide Fertilizers Derived from Instant Catapult Steam Explosion Technology: Molecular Characterization and Agronomic Efficacy

In modern agriculture, small peptide fertilizers (SPFs) have emerged as a promising tool to enhance crop growth, yield, and stress resilience. However, the influence of raw materials and innovative preparation methods on SPF characteristics and agronomic performance remains underexplored. This study introduces instant catapult steam explosion (ICSE), a novel thermomechanical technology, for synthesizing SPFs from fish, soybean meal, and sheepskin. The molecular, chemical, and nutritional properties of the SPFs were then characterized using methods including gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and HPLC/LC-MS. The research aims to characterize the molecular, chemical, and nutritional profiles of resulting SPFs and evaluate their effects on rice and rapeseed growth, yield, and nitrogen use efficiency (NUE). ICSE-generated SPFs exhibited distinct properties based on raw materials. Fish-derived SPF1 had a narrow molecular weight distribution, high small peptide content (573 mg g⁻¹), and free amino acids (0.478 mg g⁻¹), while sheepskin-derived SPF3 showed the lowest values (386 mg g⁻¹ and 0.366 mg g⁻¹, respectively). Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of peptide bonds and functional groups, with variations in peak intensities reflecting differences in raw materials. Field trials revealed that SPF1 significantly improved rice and rapeseed growth parameters, including plant height, SPAD values, and flag leaf area, compared to controls. Yield increases of 10.36% (rice) and 11.74% (rapeseed) were observed for SPF1, alongside the highest NUE (42.3–43.4%). Soybean meal-derived SPF2 showed moderate performance, while SPF3 had minimal effects. These findings validate ICSE for sustainable SPF production and emphasize the importance of selecting raw materials to optimize fertilizer outcomes and enhance crop productivity.