Overview of bacterial soil inoculants, plant growth promoting rhizobacteria (PGPR), and biological fertiliser products. Based on two articles in Direct Driller Issue 3: the editorial on biological fertilizers and Jamie Stotzka’s (PlantWorks) article on beneficial microorganisms.
Types of Beneficial Soil Microbes
Nitrogen-Fixing Bacteria
- Fix atmospheric nitrogen into plant-available forms
- Isolated from soils in Hungary and other research programmes
- Reduce dependence on synthetic nitrogen fertiliser
Phosphate and Silicate Mobilising Bacteria
- Solubilise mineral phosphates and potassium in soil
- Make otherwise locked-up nutrients plant-available
- Particularly valuable where soil P/K indices are adequate but availability is poor
Phytostimulating Strains
- Produce plant hormones and hormone-like substances
- Directly enhance plant growth and development
- Improve abiotic stress tolerance (drought, heat, cold)
[Source: dd-issue-03, 2026-04-11]
PGPR — Plant Growth Promoting Rhizobacteria
Jamie Stotzka (PlantWorks) identifies four mechanisms by which PGPR benefit crops:
- Nutrient solubilisation — making soil nutrients plant-available
- Hormone production — stimulating root and shoot growth
- Pathogen suppression — competitive exclusion of harmful microbes
- Induced systemic resistance — priming the plant’s own defences
Trial Results
| Crop | Treatment | Result |
|---|---|---|
| Sugar beet | PGPR inoculant | +33% yield increase |
| Wheat | PGPR inoculant | +10% grain weight |
| Wheat (Simon Cowell, Essex) | PGPR + AMF | +1.3 t/ha yield uplift; mycorrhizal colonisation up to 80% |
Positive PGPR × AMF interaction: when both PGPR and arbuscular mycorrhizal fungi are present and active, the combined effect exceeds either alone.
[Source: dd-issue-03, 2026-04-11]
International Evidence
Hungarian Trials
- Regulated field studies confirmed:
- +18% corn yield increase
- +39% soybean yield increase
- Inoculation success depends heavily on weather conditions
- Effects observed: increased root length, stem height, leaf number and surface area, total protein content, shoot mass, and crop yield
Global Uptake
- Hundreds of thousands of hectares treated with soil inoculants in Europe
- Usage growing rapidly in developing countries where soil degradation from chemical fertiliser overuse is severe
- China and India: chemical fertiliser use up 60% — biological alternatives increasingly necessary
[Source: dd-issue-03, 2026-04-11]
Practical Challenges in the UK
- Refrigerated storage required — products are live biological organisms with limited shelf life
- Ideally supplied just-in-time and used within days
- UV light degrades products rapidly — must be incorporated into soil quickly after application
- Best placed in the slot with seed under no-till (ideal delivery method for direct drills with liquid fertiliser capability)
- Products must be developed for specific soil pH and temperature ranges — acidic vs alkaline soils require different formulations
- UK trials underway (as of 2018) with results expected in future issues
[Source: dd-issue-03, 2026-04-11]
BioFil — pH-Specific Liquid Inoculants (Issue 4)
Hungarian-developed liquid organic bacterial soil inoculant, now available in UK via Farm Marketplace (from January 2019). 12+ years of research; 25-person research team including 3 PhD microbiologists.
Product Range
| Product | pH Range | Key Feature |
|---|---|---|
| BioFil Acidic | 4–6 | Bacteria reproduced well in acidic soils |
| BioFil Normal | 5–7 | Excellent nitrogen-fixing ability |
| BioFil Alkaline | 7–8 | Suppresses plant pathogen fungi |
| BioFil Pea/Bean | — | Pea-symbiont strains; increases nodule formation |
| BioFil Soya | — | Symbiont N-fixing strain for soya nodulation |
| BioFil Post Harvest | — | Cellulose degradation at low soil temperatures; includes N-fixing strain |
Each product contains up to 7 unique bacterial strains specifically developed for the target soil pH.
Trial Results (Hungary)
| Crop | Year | Yield increase |
|---|---|---|
| Green pea (acidic soil) | 2018 | +26.7% |
| Green pea | 2016 | +40% |
| Green pea | 2015 | +50% |
| Sunflower | 2017 | +23.1% |
| Potato | 2017 | +6 t/ha |
| Soya | Various | +9% to +42.9% |
General range: monocots +5–15%, dicots +5–25%.
Practical Notes
- Equivalent to ~100 kg/ha chemical NPK when applied as directed (through N-fixing and P/K solubilising bacteria)
- Shelf life: 6 months refrigerated (4–5°C); 1 month at 20°C
- UV degrades product — must be incorporated to 5–10cm depth (ideal for in-slot placement via direct drill)
- First UK trials started autumn 2018 on winter wheat, OSR and beans under no-till (Cross Slot and JD)
[Source: dd-issue-04, 2026-04-11]
Relevance to No-Till Systems
No-till systems are particularly well suited to biological inoculants because:
- Minimal soil disturbance preserves established microbial communities
- In-slot placement via direct drill delivers inoculants directly to the rhizosphere
- Higher baseline soil biology in no-till means inoculants integrate into a functioning ecosystem rather than being applied to degraded soil
- Reduced reliance on synthetic inputs aligns with the CA philosophy
[Source: dd-issue-03, 2026-04-11]
Related Pages
- Mycorrhizal Fungi Under No-Till — AMF diversity and PGPR×AMF interaction
- Wheat Varieties and Mycorrhizal Fungi — Variety-level AMF colonisation differences
- Soil Carbon and Organic Matter — Soil biology and organic matter cycling
- Soil Farmers of the Year 2018 — Simon Cowell’s biological approach (compost + inoculants)
- Soil Health Monitoring — In-Field Tests and Tools — Assessing soil biological activity