Synergistic effects of ammonifying bacteria and hydrochar on improving aeolian sandy soil quality for maize cultivation

B. diminuta W1 was isolated from sandy soil in Baicheng (Jilin Province, China) using compound amino acids as the sole carbon and nitrogen source, with hydrochar as a carrier. Hydrochar was produced by hydrothermal carbonization of corn straw at 200 °C for 6 h. Laboratory assays evaluated microbial growth, alkalinity production, and calcium carbonate precipitation via optical density (OD₆₀₀), pH, scanning electron microscopy (SEM), and X-ray diffraction (XRD).

Summary of findings. Results showed that B. diminuta W1 induced calcium carbonate precipitation through ammonification, reaching OD₆₀₀ = 1.578 and pH = 8.92. SEM and XRD confirmed calcite in solution and aragonite when calcium ions were adsorbed to hydrochar, indicating polymorphic transitions driven by the carbon substrate.

In pot trials, the combined hydrochar-bacteria treatment (CNJ) increased soil calcium carbonate (+71.8%), organic carbon (+66.8%), and macroaggregates (+48.4%), while reducing bulk density (-33.6%). Field water-holding capacity and plant-available water also improved markedly. Rhizosphere analysis showed enhanced beneficial fungi (e.g., Podospora) and reduced pathogens (Fusarium, Talaromyces).

Maize growth was strongly promoted in height and stem diameter, rising by 79.7% and 82.8%, while root length, surface area, and volume increased by 235.2%, 365.3%, and 189.9% over the control. Interpretation and significance. The synergistic action of hydrochar and B. diminuta created a biologically active mineral-organic matrix that improved soil structure, water and nutrient retention, and microbial community health.

Hydrochar provided colonization sites and pH buffering, while the bacterium induced in-situ precipitation of calcite and aragonite via amino acid metabolism, enhancing soil stability without excess ammonia accumulation. This eco-friendly, low-input approach offers a sustainable solution for rehabilitating aeolian sandy soils and advancing soil conservation, microbial ecology, and biogeochemical engineering.