Soil Texture Mediates the Short-Term Influence of Wheat Straw Biochar Amendment on Crop Yield and Soil Bacterial Community

Optimizing biochar use requires understanding its effects on soil microbes and crop yield, yet the role of soil texture remains unclear. In a two-year field experiment with a winter wheat–summer maize rotation on sandy and fluvo-aquic soils, biochar was applied at rates of 0, 10, and 20 t ha−1. In sandy soil, biochar increased maize yield by 9.8% in the first year and by 13.1% in the second year, and wheat yield by 8.0% in the second year. In fluvo-aquic soil, only the 10 t ha−1 rate increased maize yield by 9.7% in the second year. Biochar altered soil properties and enzyme activities in both soils, but microbial community responses varied with soil type, and soil type exerted a stronger influence than biochar application rate. In fluvo-aquic soil, the highest biochar application rate (20 t ha−1) enhanced bacterial richness and diversity with a changed community structure, increasing Acidobacteria and Chloroflexi while decreasing Proteobacteria, whereas no such effects were observed in sandy soil. These community shifts were correlated with available potassium, urease, and sucrase, factors themselves affected by biochar. Fungal diversity and community structure were unaffected in either soil. Biochar increased yields through direct physicochemical improvements in sandy soil, whereas in fluvo-aquic soil it acted via combined physicochemical and microbial effects. Overall, the effects after two years of biochar on soil microorganisms and crop yield strongly depend on soil texture, mediated by complex interactions among soil properties. Given that the study involved a single biochar type and two soil types, further research across broader conditions is needed to verify the generality of these conclusions.