Insights into Opposite and Positive Effects of Biochar and Organic Fertilizer on Red Soil Properties and Growth of Pennisetum giganteum

Biochar (BC) and organic fertilizers (OFs) are both organic soil amendments that can be used to improve soil quality, but their effects on soil physicochemical properties and microbial structures may be different. Comparative studies can help us understand the advantages and disadvantages of different types of soils. In the current research, five treatments, including a control group (CK), two concentrations of biochar (2% BC and 4% BC), and two concentrations of organic fertilizer (2% OF and 4% OF) and their effects on soil properties, enzyme activities, and bacterial diversity were evaluated. The BC and OF significantly increased the soil EC, pH, and soil nutrients (p < 0.05). The 2% BC increased the biomass of Pennisetum giganteum by 41.7%. The 4% BC and OF reduced the biomass of P. giganteum. Furthermore, the observed decrease in the P. giganteum yield following the application of the 4% BC can be attributed to reductions in the available phosphorus (AP) and CaCl2-P, as well as alterations in the soil enzyme activity. However, the negative impact of OFs on crop yield may be associated with an increased EC, elevated abundance of soil-borne pathogens, and decreased levels of beneficial microorganisms. In summary, a comparative study of the effects of BC and OF on the growth of P. giganteum in acidic soil is of great significance for improving the soil quality, promoting the development of organic agriculture, protecting the environment, and promoting land reclamation.