Narrowing the Guardrails
of Fertility Management
Summer Agronomy Conference 2025
Key Takeaways
- Fertilizer costs can vary by $72–$189/A over four years due to lab variability.
- Lab methods (dry vs. moist, ICP vs. colorimetric) produce drastically different nutrient readings.
- Sampling depth, timing, and technique significantly affect soil test accuracy.
- Yield increases—not better fertilizer use—are driving perceived efficiency gains.
- Radicle Lab offers more repeatable and accurate results, validated through real-world bucket tests.
- Farm-specific data is essential—university recommendations may not fit your field.
- Benchmarking your current lab against Radicle can reveal hidden inefficiencies.
What to Expect
Hear from Radicle Agronomics’ Drew Reynolds—an experienced agronomist from Kentucky—as he dives deep into the complexities and inefficiencies of current soil fertility management practices. With over two decades of field experience, he challenges conventional norms and introduces a data-driven approach to improving nutrient management through more accurate soil sampling and lab analysis.
While common soil sampling methods and fertilizer recommendations have not changed in decades, variability in sampling methods, lab procedures, and interpretation of results can significantly impact return on investment (ROI) for farmers. Fertilizer is a major budget item—up to $250 per acre for corn—and even small inaccuracies can lead to thousands of dollars in lost efficiency.
Insights
- Precision Soil Sampling Evolution: From broad field samples to 2.5-acre grids, sampling density has increased, but accuracy remains inconsistent due to human error and lack of standardization.
- Fertilizer Efficiency Trends: Over 22 years, fertilizer efficiency (pounds of nutrient used per bushel of yield) has improved not because of better application, but due to increased yields driven by other technologies.
- Sampling Variability: Soil type, slope, elevation, and sampling depth all introduce variability. Even the timing of sampling (fall vs. spring) can drastically affect nutrient readings.
- Lab Analysis Discrepancies: Different labs use different testing methods (e.g., Mehlich 3 ICP vs. colorimetric), leading to wide variations in results and recommendations—even within the same state.
- Bucket Test Validation: Radicle’s “bucket test” homogenizes soil samples and compares lab results over time, revealing significant variance in nutrient readings across different commercial labs.
- Real-World Impact: In one 43-acre field test, phosphorus recommendations varied by up to $9.30/acre and potassium by $26.50/acre depending on the lab—compounding to over $100/acre across four years.
Next Steps
So where do we go from here? The clear message is that farmers and agronomists must take control of their data. By participating in Radicle’s bucket tests, nutrient response trials, and soil collection studies, you can reduce variability, improve ROI, and make more informed decisions tailored to your unique fields.
