What are the specific roles of Bacillus subtilis in soil improvement?

      Bacillus subtilis plays a multidimensional role in soil improvement, and its core functions and mechanisms are as follows:

1、 Nutrient activation and cycling

Phosphorus and potassium solubilization function

      By secreting phytase and organic acids (such as citric acid and gluconic acid), insoluble phosphates (such as calcium phosphate) in soil can be converted into water-soluble phosphates that can be absorbed by plants, with an activation efficiency of up to 30% -50%. At the same time, its secreted extracellular polysaccharides can chelate potassium ions, releasing fixed potassium from minerals such as mica and feldspar for crop utilization.

Nitrogen fixation synergy effect

      Although lacking nitrogen fixation ability, it can promote the proliferation of nitrogen fixing bacteria (such as rhizobia) in the rhizosphere by secreting growth factors (such as vitamin B12), indirectly increasing soil nitrogen levels.

2、 Soil structure optimization

Reshaping of granular structure

      The secreted extracellular polysaccharides combine with soil particles to form water stable aggregates with a diameter of 0.25-10mm, increasing soil porosity by 15% -20% and improving aeration and permeability.

Accelerated synthesis of humus

      When decomposing organic matter such as crop straw, it is converted into humic acid (molecular weight 3000-5000Da) and fulvic acid (molecular weight<1000Da), increasing soil organic matter content by 0.1% -0.3% per year.

3、 Construction of biological control system

Pathogen inhibition network

      Secreting lipopeptide antibiotics (such as surfitin and fengycin) can damage the cell membrane of pathogenic bacteria and inhibit the growth of Fusarium hyphae by 65% -80%.

      Producing chitinase and β -1,3-glucanase, degrading the cell wall of pathogenic bacteria, with an inhibition rate of over 90% on the germination of gray mold spores.

Induced Systemic Resistance (ISR)

      Activate the activities of phenylalanine ammonia lyase (PAL) and peroxidase (POD) in plants, increase the content of salicylic acid (SA) by 2-3 times, and enhance the crop's defense against root rot and bacterial wilt.

4、 Alleviation of environmental stress

Heavy metal passivation

      The secreted extracellular polymeric substances (EPS) can chelate Cd ²+and Pb ²+ions, forming stable complexes and reducing their bioavailability. The pot experiment showed that the cadmium content in rice in Cd contaminated soil decreased by 42%.

Salinization improvement

      By accumulating compatible solutes such as betaine, maintaining cell osmotic pressure, and promoting the proliferation of salt tolerant microorganisms (such as halophilic cocci) in the soil, tomato yield under NaCl stress can be restored by over 75%.

5、 Effect time and application parameters

Colonization dynamics

      Spores germinate within 24 hours after application to the soil, reaching the population peak (10 ⁷ -10 ⁸ CFU/g soil) within 7-10 days, and the duration of action can reach 3-6 months.

synergy effect

      When combined with arbuscular mycorrhizal fungi (AMF), it can promote fungal hyphal extension and increase phosphorus absorption rate by 40%; Mixing with organic fertilizer can increase the survival rate of spores to over 85%.

6、 Typical application data

      Northeast Black Soil: After applying Bacillus subtilis preparations for three consecutive years, the soil bulk density decreased from 1.35g/cm ³ to 1.18g/cm ³, and the field water holding capacity increased by 9%.

      Saline alkali land in North China: After inoculation of strain B16, the soil pH decreased from 8.5 to 7.8, and the incidence rate of cotton wilt disease decreased from 28% to 9%.

      Southern Red Soil: The phosphate solubilizing bacterium strain PSB-1 increased the effective phosphorus content from 8.2mg/kg to 19.7mg/kg, resulting in an 18.6% increase in rapeseed yield.

      This bacterium achieves systematic improvement of soil from physical structure to biological function through a triple mechanism of material cycling reconstruction, microbial community regulation, and plant physiological activation, providing an important biological solution for sustainable agriculture.