Labile carbon drives synergistic improvements in Astragalus membranaceus yield and quality under chemical fertilizer reduction combined with organic amendments

Over-fertilization and soil organic matter deficiency are common problems in Astragalus membranaceus (A. membranaceus) cultivation, severely limiting its yield and quality. This study conducted a field experiment to investigate the effects and underlying mechanisms of chemical fertilizer reduction combined with organic amendments (CFR+OA) on the yield and quality of A. membranaceus . The objective was to evaluate the practical feasibility of CFR+OA technology for A. membranaceus and to identify the key factors affecting its yield and quality by analyzing basic soil physicochemical properties, labile carbon fractions, and enzyme activities. Five treatments were tested: (i) farmer practice (FP), (ii) chemical fertilizer reduction (CFR), and three CFR+OA combinations—(iii) organic fertilizer (OF), (iv) bio-organic fertilizer (BOF), and (v) vermicompost (Vm). Results showed that CFR+OA treatments enhanced the yield, quality, and profit of A. membranaceus , with BOF exhibiting superior performance. Compared with FP, BOF treatment significantly increased root dry weight and active constituent yield (ACY) by 9.86% and 43.31%, respectively, and increased profit by 1,897.23 USD·ha - ¹. In addition, CFR+OA treatments significantly improved soil properties. Compared with FP, BOF treatment markedly increased soil available nutrients (AP, AK), labile carbon fractions (POC, ROC, DOC, MBC), and enzyme activities (S-UE, S-SC, S-ALP) by more than 15%, with AP, POC, MBC, and S-ALP increasing by over 50%. The Random Forest analysis identified TN, AK, POC, MBC, and S-SC as key common drivers that significantly influence the RDW and ACY of A. membranaceus ( P < 0.05). Among these, POC was the only factor showing a highly significant positive effect on both yield and ACY ( P < 0.01). This result indicates that the soil labile carbon pool, dominated by POC, plays a critical role in regulating the yield and quality of A. membranaceus . In conclusion, this study demonstrates that CFR+OA is validated as a fertilization technology for Hengshan A. membranaceus cultivation, achieving the goal of “carbon-fertilizes-soil, carbon-boosts-yield”. CFR+BOF effectively improves soil properties and enhances the yield and quality of A. membranaceus , demonstrating great potential for widespread application.