Overview
Presentation on biological soil testing focused on the Haney test, explaining its development, differences from traditional testing, and application for reducing fertilizer inputs while accounting for microbial nutrient cycling.
Origin Story and Lab Development
- Speaker worked at Ward Laboratories for 17 years, started soil health division in 2010
- Background in biology and chemistry, not soil science or agronomy
- Left in 2019 to start dedicated lab for farmers transitioning to regenerative practices
- Borrowed significant funds after 12 rejections and 1 approval
- First samples arrived October 19, 2019 from Gabe Brown before building was complete
- Received 60,000 samples between October 2019 and October 2020 opening
- Customers willing to wait months for results demonstrated market need
Soil Microbiology and Ecosystem Function
- Soil functions like a gut; microbes facilitate nutrient uptake, not just passive absorption by roots
- Microbes build and break down organic matter, influence N, P, C, zinc, cobalt availability
- Predation between microbes drives nutrient cycling
- Tillage speeds up soil structure destruction, but microbes cause it
- Microbes remodel aggregates every 3 weeks (analogous to every third generation)
- Bacterial populations: 100 million per gram (teaspoon) of soil
- Actinomyces bacteria break down lignified material; responsible for "fresh tilled earth" smell
- 90% of antibiotics come from actinomyces group; they naturally suppress plant diseases
- Fungi transport water, P, N, zinc, copper based on plant signals
- Mycorrhizal fungi are obligate symbionts (die without host plant)
Microbial Groups and Roles
| Group | Function | Notes |
|---|
| Bacteria | Dominate landscape in numbers; cycle nutrients | 10⁸-10⁹ per gram of soil |
| Actinomyces | Break down lignified material (corn stalks) | Filamentous bacteria; produce antibiotics |
| Saprophytic Fungi | Break down lignified material with actinomyces | Work with white/brown rot fungi |
| Mycorrhizal Fungi | Transport nutrients; increase drought resilience | Obligate symbionts; die without host |
| Algae | Fix nitrogen; add carbon via photosynthesis | Function as free cover crop between rows |
| Protozoa | Graze on bacteria; release nutrients | Eat 10,000 bacteria/day; excrete plant-available nutrients |
| Nematodes | Feed on bacteria and fungi | Most are beneficial, not harmful |
Traditional Soil Testing History
- Tests developed in 1940s-50s alongside fertilizer development
- Designed to measure plant-available chemistry and sell fertilizer
- Bray P1 (1945): Works well on low CEC, low pH, low organic matter soils
- Olsen (1954): Bicarbonate extraction for calcareous soils; pH ~11-12
- Mehlich 1 (1953): Standard in Georgia; still used in Carolinas
- Mehlich 2 (1978): Complete flop; rarely used
- Mehlich 3 (1984): Most common; 12 million soil samples run annually in U.S.
- Problem: Standard tests east of Mississippi often exclude nitrogen testing
Haney Test Development (H3A Extract)
- Developed by Rick Haney (soil chemistry background)
- Goal: Create extract mimicking natural soil solution, not lab-only chemicals
- Initially tested with Seven Up (correlated well with Mehlich 3)
- H3A uses citric acid, oxalic acid, malic acid (plant-derived compounds)
- Four versions developed; H3A version 4 removed lithium citrate buffer
- Works across pH range 4.5 to 9.5 without overpowering natural soil system
- Maintains soil pH during extraction (Mehlich 3 forces to pH 3.2; Olsen forces to pH 11-12)
- Correlation to standard tests: R² = 0.95 (potassium), 0.87 (nitrate), 0.82 (phosphorus)
Testing Components and Measurements
- Total Nutrient Digest: Measures net worth/total assets in soil (e.g., 2,300 lbs P/acre top 8 inches)
- H3A Extract: Measures checking account/readily available nutrients
- Soil Respiration: Measures microbial biomass by CO₂ release when soil rewets
- Respiration indicates nutrient cycling rate, residue decomposition, soil aggregation
- Higher respiration = larger "biological fire" for breaking down residues
- Water Soluble Carbon (WSC): Food in the pantry for microbes; readily available energy source
- Soluble Protein: Benefits package for microbes; tied to nitrogen release
Nitrogen Cycle and Carbon Dynamics
- Traditional focus only on inorganic nitrogen (nitrate); ignores hundreds of other N compounds
- 50% of carbon captured by corn released through roots while plant is alive
- This carbon feeds microbes who provide nutrients in return (symbiotic exchange)
- Water soluble carbon fluctuates seasonally; freeze-thaw increases breakdown initially
- Respiration follows seasonal pattern with dip around week 25 (resource consumption exceeds production)
- Cover crops bridge the gap, preventing microbes from consuming soil organic matter structure
- Negative carbon balance: Microbes consume soil structure carbon when food sources depleted
- Maintaining positive carbon balance prevents soil crusting and compaction
Seasonal Patterns
| Time Period | Without Cover Crop | With Cover Crop |
|---|
| Early Spring (Weeks 1-20) | Low respiration; freeze-thaw breakdown | Earlier biological priming; higher respiration |
| Mid-Season (Week 25) | Large trough; resource depletion | Smaller dip; resources bridged |
| Growing Season (Weeks 30-50) | Recovery as crops feed microbes | Sustained higher activity |
| Carbon Balance | Often negative mid-season | Remains positive; no structure loss |
Nitrogen Credit Comparison
- Traditional Method: Credit only for nitrate (example: 44 lbs/acre)
- Haney Method: Credit for nitrate + ammonium + organic nitrogen release (example: 121 lbs/acre)
- Average organic N release: 20 lbs/acre (healthy systems: 100-140 lbs/acre)
- Example corn at 200 bushels: Traditional recommends 175 units N; Haney recommends 100 units N
- Corn grain removal: 0.7 lbs N per bushel; standard recommendation: 1.1 lbs per bushel
- Excess fertilizer: Microbes consume unused N when underfed; return it when properly fed
Fertility Recommendation Framework
- Both methods account for: crop type, yield goal, soil test credit, past crop credit, subsoil nitrate
- Haney adds: credit for ammonium and organic N release from microbial activity
- Traditional tests miss biological contribution to nutrient availability
- Recommendations based on actual soil biological function, not just chemistry
- No recommendation of zero fertilizer; goal is accurate accounting of what's truly available
Key Terms and Definitions
- Aggregate: Soil structure unit smaller than 1 millimeter (not a dirt clod)
- Obligate Symbionts: Organisms that cannot survive without their partner (e.g., mycorrhizal fungi and plants)
- Geosmin: Volatile organic compound released by actinomyces; "fresh tilled earth" smell
- Organic (chemistry): Carbon-based compounds; not referring to organic farming practices
- C:N Ratio: Carbon to nitrogen ratio; bacteria = 3:1, corn at maturity = 80:1
- Mineralization: Process where microbes convert organic nutrients to plant-available forms
- Water Soluble Carbon: Readily available carbon food source for microbes (food in pantry)
- Total Nutrient Digest: Measures total nutrients in soil (asset evaluation/net worth)
Action Items and Recommendations
- Choose soil tests based on operation goals, not one-size-fits-all approach
- For conventional farming with no planned changes: stick with traditional tests
- For regenerative/transitional systems: biological tests become more valuable
- Use total nutrient digest to understand true soil reserves versus annual additions
- Measure microbial biomass to gauge biological fire strength before adding large amounts of residue
- Start cover crops with brassicas and legumes initially to build biological fire
- Progress to grass covers as microbial activity increases
- Take credit for biological nitrogen production; adjust fertilizer rates accordingly
- Focus on maintaining positive carbon balance to prevent soil structure loss
- Feed microbes consistently to improve nutrient use efficiency and reduce input costs