Mealworm frass-based biofertilizer improves soil nutrient profile and Chinese kale growth parameters towards sustainable agriculture

Abstract Modern agriculture requires alternatives to counteract the price volatility and environmental impacts of synthetic fertilizers. Mealworm frass (MF) is being explored as a novel biofertilizer in sustainable agriculture. However, the in-depth characterization of its biofertilization potential is lacking. Similarly, the mechanistic role of its associated microbiota towards improving early plant growth response is unexplored. These are the gaps the current study addresses. Initially, the particle size and nutrient distribution of the MF were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Subsequently, microbial isolation and molecular identification characterized the MF-associated microbiome. Isolates were thereafter screened via various plant growth promotion (PGP) assays. Nutrient mineralization rates were calculated through soil incubation experiments. MF and chicken manure (CM) were incorporated into the soil at 1% (w/w) using a Completely Randomized Design (CRD) with three replications. Additionally, the effects of the MF on Chinese kale (CK) growth and yield were evaluated under greenhouse conditions using a Randomized Complete Block Design (RCBD). The results showed that MF had uniform nutrient distribution: high organic matter content (63.38%), the presence of essential nutrients (5.09% N, 1.71% P, and 2.82% K), and a low C:N ratio (6.69). Furthermore, the characterized MF microbiota comprised plant growth-promoting genera such as Streptomyces , Microbacterium , Brucella , Staphylococcus , and Rothia , which fix nitrogen, solubilize K & P, and produce IAA. Moreover, nutrients were released rapidly for plant uptake (7-day nitrogen mineralization rate = 93.75 mg kg −1 day −1 ). The CK growth trials showed that MF + 50% chemical fertilizer (CF) yielded the highest fresh weight (141.73 g plant −1 ) and crop quality (vitamin C: 227.97 mg plant −1 ; antioxidant activity: 238.10 µmol TE g −1 ). Usually, MF alone and MF + 50% CF outperformed CF and CM alone, respectively, in improving various plant growth responses, nutrient uptake, antioxidant activity, and vitamin C content ( p < 0.05). Taken together, our findings mechanistically portray MF (aided by PGP microbiota) as a biofertilizer for both organic and integrated farming systems. Further scale-up studies are recommended to fully justify the use of MF biofertilizer as a substitute for CF towards circular economy and agricultural sustainability principles. Graphical abstract