Amending Soil With <scp> <i>Sonchus Oleraceus</i> </scp> Residue Enhances Soil Microbial Function and Nutritive Composition of Cowpea ( <scp> <i>Vigna unguiculata</i> </scp> ) Seeds

ABSTRACT Enhancing soil function through residue‐based amendments is an important strategy for improving crop quality in sustainable and restoration‐oriented agriculture. This study evaluated whether incorporating Sonchus oleraceus residue into soil could improve microbial activity, soil biochemical properties, and the nutritional composition of cowpea ( Vigna unguiculata (L.) Walp.) seeds under field conditions. Residue incorporation consistently enhanced soil organic matter and key microbial indicators, reflecting improved nutrient cycling and soil biological functioning. These changes were associated with notable increases in essential minerals, amino acids, sugars, phenolics, flavonoids, vitamins, and unsaturated fatty acids in cowpea seeds. Multivariate analyses further showed clear associations between improved soil biochemical status and metabolite enrichment. Overall, the findings demonstrate that S. oleraceus residue acts as an effective soil amendment that strengthens soil fertility and enhances seed nutritional quality, supporting its potential role in sustainable cropping systems and soil restoration frameworks.