Cotton Straw Composting by Exogenous Microorganisms and the Improvement Effect on Desert Soil

Aerobic composting by microbial inoculation is a green and mild way to handle biomass. Here, three bacterial strains, including Bacillus halotolerans, Bacillus velezensis, and Bacillus subtilis, were compounded to obtain microbial agents, which were further used to obtain cotton straw compost. During this process, the influence of inoculation on cotton straw composting and the relatedness among its physicochemical properties are discussed. Results showed that inoculation extended the thermophilic period by 1–4 days and enhanced subsequent degradation of organic matter. The compost products were made to be fully decomposed, and the germination index (GI) of each treatment group all exceeded 80%. In particular, composting with microbial inoculants containing Bacillus velezensis and Bacillus halotolerans (1:1, treatment PM63-CS) resulted in higher total nitrogen (TN), total phosphorus (TP), total potassium (TK), and humic acid (HA) contents. The influence of microbial agents on structural changes in resultant cotton straw compost was characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption–desorption techniques. Analysis based on 16S rRNA gene sequencing indicated that inoculation improved the richness and diversity of the bacterial community. The interactions between microorganisms and environmental factors facilitated organic matter degradation and humification, which collectively influenced compost maturity. Furthermore, the application of PM63-CS to desertified soil improvement effectively enhanced the nutrient content of sandy soil and promoted the growth of cotton plants. In summary, the composite bacterial agent developed in this study can effectively improve the quality and maturity of compost products, potentially providing a feasible microbial-enhanced composting approach for the resource utilization of cotton straw.