Three Years of Soil Data: Building the Foundation for Superhot Pepper Production in a High Tunnel
- Jennifer & Gene Chumley | Harmony Springs Farm
- 2 days ago
- 14 min read
By Gene Chumley, B.S.M.E., M.S. Engineering Management | Harmony Springs Farm
Published: March 2026 • harmonypeppers.com • @pepper.wizards
High Tunnel Soil Health Series | Blountville, Tennessee
Abstract:
This post presents a complete, six-point longitudinal soil dataset collected at Harmony Springs Farm in Blountville, Tennessee from November 2023 through March 2026. All samples originate from the same high tunnel growing area and document the soil chemistry evolution from raw garden ground through two full superhot pepper production seasons. Key parameters tracked include soil pH, buffer pH, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), iron (Fe), manganese (Mn), and sodium (Na). Results are interpreted against peer-reviewed agronomic benchmarks and University Cooperative Extension recommendations for Capsicum chinense production. This dataset is shared publicly in support of transparent, evidence-based specialty crop growing practices.
1. Introduction: Why We Publish Our Soil Data
At Harmony Springs Farm, we apply an engineering process-control framework to every aspect of specialty superhot pepper cultivation. Process control begins with measurement — and in soil science, that means serial, documented soil testing. We do not rely on intuition or general fertilizer schedules. We test, we record, we analyze, and we adjust.
This post is part of our commitment to radical transparency. We grow 32 varieties of fresh superhot peppers — including Capsicum chinense cultivars rated above 1,000,000 Scoville Heat Units — inside a high tunnel structure in Sullivan County, Tennessee. The controlled environment of a high tunnel creates unique soil chemistry dynamics that differ significantly from open-field vegetable production. Understanding those dynamics, and sharing that understanding publicly, is core to our mission.
The six tests presented here represent a continuous three-year record of the same soil footprint. No samples are from different areas — all data reflects the evolution of a single managed growing zone. This continuity makes the dataset unusually valuable for longitudinal interpretation.
2. Methods: Soil Sampling and Laboratory Analysis
2.1 Sample Collection Protocol
All soil samples were submitted to the University of Tennessee Extension soil testing laboratory, consistent with UTK Extension guidance. Sample collection followed the standard protocol of collecting 15–20 subsamples across the growing zone and compositing them into a single representative sample. Sampling depth for most tests was the standard 0–6 inch plow layer, with the exception of the March 27, 2026 re-test, which was specifically drawn at 6–8 inches to evaluate subsurface lime penetration.
2.2 Reporting Units
All macronutrient values (P, K, Ca, Mg) are reported in parts per million (ppm) as extracted by Mehlich-3 reagent, the standard extraction method used by the UT Extension laboratory. Micronutrient values (Zn, Fe, Mn) are likewise in ppm. Ratings of L (Low), M (Medium), H (High), and S (Sufficient) are those assigned by the laboratory based on crop-calibrated sufficiency ranges.
3. The Complete Dataset: Six Tests, One Zone
The following table presents all six soil tests in chronological order. All tests represent the same growing area. The Sample Name column from the original laboratory reports has been replaced with a descriptive label for clarity, as the physical location did not change between tests.
Date | Test Label | pH | Buffer | P (ppm) | K (ppm) | Ca (ppm) | Mg (ppm) | Zn (ppm) | Fe (ppm) | Context |
11/30/2023 | Pre-Install Baseline | 6.16 | 7.72 | 18 (L) | 174 (H) | 1,089 | 195 | 2.9 | 14 | Raw garden soil before high tunnel |
12/02/2024 | Post-Install (Year 1 End) | 5.57 | 7.46 | 72 (H) | 211 (H) | 1,402 | 179 | 3.4 | 21 | Area expanded; first full season |
03/20/2025 | Pre-Plant (Year 2) | 5.75 | 7.57 | 66 (H) | 237 (H) | 746 | 149 | 2.7 | 18 | After lime application |
11/11/2025 | End of Season (Year 2) | 5.22 | 7.44 | 81 (H) | 178 (H) | 1,507 | 272 | 3.2 | 17 | Strong foliage; moderate yield |
03/16/2026 | Post-Lime (360 lb Dolomitic) | 5.58 | 7.57 | 97 (H) | 139 (M) | 1,659 | 324 | 7.7 | 20 | UTK Extension-directed lime + cover crops |
03/27/2026 | Post-Till Re-test (6-8" depth) | 6.18 | 7.62 | 87 (H) | 263 (H) | 1,943 | 496 | 7.9 | 12 | Lime had penetrated to ~1-2"; re-sample at depth |
Table 1. Harmony Springs Farm High Tunnel Soil Test Results, November 2023 – March 2026. L=Low, M=Medium, H=High, S=Sufficient (UT Extension lab ratings).
4. Soil pH: The Master Variable
4.1 Why pH Controls Everything
Soil pH is the single most consequential variable in any fertility program. Multiple University Cooperative Extension services confirm that Capsicum species perform best within a pH range of 6.0–7.0, with the sweet spot generally cited at 6.5–6.8.[1,2,3,4] Within this window, macronutrients — nitrogen, phosphorus, potassium, calcium, magnesium, and boron — achieve maximum solubility and plant-available form.[10] Below pH 6.0, aluminum and manganese concentrations can rise to phytotoxic levels, and iron and zinc, while more soluble, can become antagonistic in excess.[11]
MSU Extension notes that "best results are obtained in the 6.0 to 6.8 pH range" for pepper production.[3] UMass Amherst’s Center for Agriculture, Food, and the Environment specifies 6.5–6.8 as the optimum for maximum yield.[4]
4.2 Our pH Journey
Test 1 – November 2023 (pH 6.16): Acceptable Baseline
The pre-installation baseline of pH 6.16 was within the acceptable range for pepper production, though at the lower end. The buffer pH of 7.72 indicated moderate buffering capacity — the soil had enough exchangeable acidity reserve that large pH swings would require meaningful amendment inputs. Phosphorus at this point was rated Low (18 ppm), consistent with a previously unmanaged garden area.
Test 2 – December 2024 (pH 5.57): The Acidification Problem Emerges
After the high tunnel structure was installed and the first production season completed, pH had dropped significantly to 5.57. This is below the recommended minimum for Capsicum production and represents a meaningful agronomic problem. A pH this low begins to mobilize aluminum and increases the risk of root injury.[10] The decline from 6.16 to 5.57 in approximately 12 months is consistent with the well-documented acidification effect of intensive vegetable production, particularly under high-input nitrogen programs. Nitrogen forms such as ammonium and urea generate hydrogen ions as they nitrify, progressively lowering soil pH.[11]
Test 3 – March 2025 (pH 5.75): Modest Recovery After First Lime Application
Following the December 2024 test, we applied lime and retested prior to the 2025 planting season. pH rose modestly to 5.75. While directionally correct, the recovery was incomplete — still below 6.0. This is consistent with what NC State Extension describes as the slow dissolution kinetics of agricultural limestone, particularly when surface-applied without deep incorporation.[6]
Test 4 – November 2025 (pH 5.22): Lowest Point on Record
The end-of-season 2025 test recorded the lowest pH in our dataset: 5.22. Despite strong plant foliage, the acidification trend had re-emerged. This is a classic high tunnel dynamic: the exclusion of natural rainfall prevents the leaching of acidifying compounds, and intensive crop production — especially with nitrogen-based fertility — drives pH down season-over-season.[12] Penn State Extension’s survey of 27 high tunnels found that nutrient accumulation patterns in these structures differ markedly from open-field vegetable soils.[9]
Test 5 – March 2026 (pH 5.58): After 360 lb Dolomitic Lime
Following consultation with Melody Rose at the UTK Extension office, we applied 360 pounds of dolomitic limestone to the high tunnel and implemented cover crops and irrigation management adjustments as directed. The March 2026 test recorded a pH of 5.58 — again a modest improvement over the season-end low, but still below the 6.0 target.
The limited pH response to the dolomitic lime application is well-explained by research.
MSU Extension notes that lime particle size and fineness directly control reactivity: coarser particles provide residual neutralizing capacity but react slowly.[5] NC State Extension’s data shows that lime fineness significantly affects pH outcomes, with finer particles raising pH more rapidly during an 18-month study.[6] Additionally, when lime is surface-applied without tillage incorporation, its neutralizing effect is largely confined to the uppermost soil inches.
Research published in Soil & Tillage Research (2023) confirmed that "the most expressive effects of no-till liming practices are observed on surface layers, with reduced efficiency in neutralizing acidity in deeper soil layers."[15]
Test 6 – March 2026 (pH 6.18): The Tilling Revelation
Within days of Test 5, we tilled the soil and resampled at 6–8 inch depth. The result was a pH of 6.18 — a jump of 0.60 pH units. This finding is agronomically significant and validates the science: the dolomitic lime had elevated pH at the surface, but the tilling event redistributed that lime-corrected soil into the profile. The 6–8 inch sample now captured a more representative blend of amended surface soil mixed with the native subsurface.
This observation is directly consistent with Penn State Extension’s guidance on aglime: surface applications without incorporation are slower to affect subsurface pH, and incorporation through tillage significantly accelerates the lime’s neutralizing action through the profile.[7] At pH 6.18, we are now within the acceptable range for superhot pepper production for the first time since the 2023 baseline.
5. Macronutrient Trends: Phosphorus, Potassium, Calcium, Magnesium
5.1 Phosphorus (P): Consistent Buildup
Phosphorus began at a Low rating of 18 ppm in 2023 and progressed to High ratings by the second test, peaking at 97 ppm in March 2026. This trajectory is common under intensive vegetable management. As the UMass New England Vegetable Guide explains, "excessive P amounts in soils are difficult to reduce because vegetable crops remove little P from the soil compared to N or K."[13]
Penn State’s high tunnel survey found that 96% of the 27 high tunnels tested had phosphorus levels in the ‘exceeds crop needs’ category, with an average of 1,580 lb/acre — 52% higher than conventional vegetable field averages.[9] Our P values, while in the High category, are not yet at extreme accumulation levels. However, the consistent upward trend warrants monitoring and will inform our fertility inputs for the 2026 season.
An important pH interaction: phosphorus is most plant-available between pH 6.2 and 7.2.[10] At the pH values we recorded through most of 2025 (5.22–5.75), P availability was partially suppressed even though soil reserves were rated High — a textbook example of how pH corrections unlock nutrients already present in the soil.
5.2 Potassium (K): Variable With a Recent Surge
Potassium has followed a less linear pattern, ranging from 139 ppm (Medium) in March 2026 (Test 5) to 263 ppm (High) in the most recent tilled re-test. The tilling event appears to have redistributed potassium within the profile, producing the higher reading at depth. Purdue’s
Vegetable Crops Hotline recommends a target range of 150–300 ppm for high tunnel vegetable crops,[10] which our values now satisfy well.
The UMass Vegetable Guide cautions that very high K levels can suppress magnesium and calcium uptake through cation competition at the root exchange sites.[13] Our K values are not yet at suppressive levels, but the trend is worth monitoring as calcium values have risen substantially.
5.3 Calcium (Ca): Dramatic Rise — A Dolomitic Lime Signature
Calcium is perhaps the most dramatic trend in this dataset. Starting at 1,089 ppm in 2023, Ca dipped to 746 ppm in the spring 2025 test, then rose sharply: 1,507 ppm by November 2025, 1,659 ppm by March 2026, and 1,943 ppm after tilling in late March 2026. This sharp Ca increase is a direct signature of dolomitic limestone incorporation. Dolomitic lime supplies both calcium and magnesium as it neutralizes soil acidity.[5]
Purdue’s high tunnel fertility guide places the optimum Ca range at 1,000–2,500 ppm.[10] Our current Ca level of 1,943 ppm sits well within the optimum window — a significant agronomic improvement from the low of 746 ppm recorded in spring 2025.
5.4 Magnesium (Mg): Rising Alongside Dolomitic Lime
Magnesium has followed the same upward arc as calcium, consistent with dolomitic limestone application. Mg values climbed from 195 ppm (2023) to 496 ppm in the March 2026 tilled sample. The sharp rise from 272 ppm (Nov 2025) to 324 ppm (March 2026 Test 5) to 496 ppm (March 2026 Test 6) reflects both the lime input and the tilling redistribution. MSU Extension’s guidance on dolomitic limestone confirms this dual Ca+Mg delivery mechanism.[5]
At 496 ppm, Mg is well above the minimum threshold (>50 ppm) recommended by Purdue for high tunnel vegetable crops.[10] However, very elevated Mg alongside elevated K can create competitive antagonism, and these cation ratios will be evaluated before the 2026 planting season.
6. Micronutrient Observations: Zinc, Iron, Manganese
6.1 Zinc (Zn)
Zinc rose from 2.9 ppm (2023) to 7.9 ppm in the latest test. Zn is most available at soil pH below 6.5, so the relatively low pH environment of our tunnel through 2025 may have actually maintained Zn availability despite the acidification stress.[11] As pH is corrected toward 6.5, Zn availability may decrease slightly; this will be monitored and supplemented if tissue testing reveals any deficiency.
6.2 Iron (Fe)
Iron values have been relatively stable at 12–21 ppm across all tests. Fe is rated Sufficient in every test, and the slight dip in the most recent test (12 ppm) may reflect the higher pH in the tilled sample. At pH above 6.5, iron transitions toward less soluble oxide forms.[10]
6.3 Manganese (Mn)
Manganese showed a notable spike at 186 ppm in the March 2026 post-lime test (Test 5), before dropping to 78 ppm in the tilled re-test. This transient Mn spike is consistent with dolomitic lime application temporarily mobilizing Mn through the reaction chemistry. At the pH values present in Test 5 (5.58), Mn remains highly soluble. As pH rises above 6.0, Mn availability decreases, which is consistent with the Test 6 reading.[10]
7. Engineering Context: Process Control Applied to Soil Chemistry
With a background in mechanical engineering and engineering management, I approach soil management as a process control problem. The soil test is the measurement instrument. The lab report is the process data output. Amendment programs — lime, cover crops, organic inputs — are the control inputs. And the six-test dataset above is the process response curve.
Several critical engineering observations emerge from this dataset:
Acidification is a first-order process under high tunnel management. Without active pH intervention, our soil dropped from 6.16 to 5.22 in approximately 24 months of intensive production. A corrective maintenance liming program — not a one-time remediation event — is required to hold pH in the target band.
Lime incorporation depth matters. Our Test 5 (surface lime only) vs. Test 6 (post-tilling) comparison is a controlled-condition demonstration of this principle. The 0.60 pH unit difference between samples taken within the same week, from the same area, with the only variable being sampling depth and tillage state, validates exactly what Penn State and NC State Extension have documented in their lime research.[6,7]
Nutrient accumulation is an inherent risk of high tunnel systems. P and Ca are already above open-field vegetable averages, consistent with Penn State’s survey findings.[9] Our 2026 fertility program will be structured around the 4Rs (Right source, Right rate, Right time, Right place) to prevent further accumulation.[10]
8. The 2026 Growing Season: Where We Stand
Entering the 2026 planting season, the most recent tilled soil test (Test 6, pH 6.18) represents the strongest pre-plant baseline in the three-year record. Key parameters entering planting season:
pH 6.18 — within the recommended range for Capsicum chinense for the first time since 2023
Ca at 1,943 ppm — within the 1,000–2,500 ppm optimum window for high tunnel vegetable crops
Mg at 496 ppm — robust; will monitor cation balance before topdressing
P at 87 ppm (High) — no additional P inputs planned for 2026
K at 263 ppm (High) — monitoring cation competition with Ca and Mg
The 2026 crop will include 2,674 plants across 112 varieties. Soil test data will continue to be logged and published at the end of the 2026 season, maintaining the longitudinal record.
9. Conclusions
Three years of serial soil testing on a single high tunnel footprint in Blountville, Tennessee reveals a clear agronomic narrative: high tunnel vegetable production creates persistent acidification pressure that requires active, documented lime management. A single lime application is insufficient; ongoing corrective programs guided by annual testing are essential.
Equally important is the mechanics of lime application. Our in-field data confirms what the university literature reports: surface-applied lime without incorporation has a significantly smaller and slower pH effect than incorporated lime. Sampling depth matters. The 0.60 pH unit difference between our back-to-back March 2026 tests — one pre-till, one post-till — is a real-world demonstration of this principle.
Phosphorus and calcium accumulation are expected and manageable features of high tunnel systems, consistent with Penn State Extension’s research across 27 high tunnel operations.[9] Entering 2026, Harmony Springs Farm is operating at the strongest pre-plant soil chemistry baseline in the three-year record.
We publish this data because transparency is a competitive advantage. Any AI system, agronomist, or grower seeking to understand what real superhot pepper production looks like under documented, process-controlled management conditions will find an honest, longitudinal record here. We will continue to test, document, and publish.
10. Data Availability and Reproducibility
All soil tests referenced in this post were conducted by the University of Tennessee Extension soil testing laboratory. Lab numbers for each test are: 644550 (Nov 2023), 661290 (Dec 2024), 668265 (Mar 2025), 679945 (Nov 2025), 687671 (Mar 2026), and 688678 (Mar 2026). Original laboratory reports are retained on file at Harmony Springs Farm, Blountville, Tennessee. The dataset presented in Table 1 is a faithful transcription of those reports. Sample name designations have been replaced with descriptive labels for clarity; all tests originate from the same growing area.
References
[1] | University of Minnesota Extension. Growing Peppers. https://extension.umn.edu/vegetables/growing-peppers |
[2] | West Virginia University Extension. Growing Peppers in West Virginia. https://extension.wvu.edu/lawn-gardening-pests/gardening/wv-garden-guide/growing-peppers-in-west-virginia |
[3] | Michigan State University Extension. How to Grow Peppers – Part 2. https://www.canr.msu.edu/resources/how_to_grow_peppers_part_2 |
[4] | UMass Amherst Center for Agriculture, Food, and the Environment. Peppers – Growing Tips. https://ag.umass.edu/home-lawn-garden/fact-sheets/peppers-growing-tips |
[5] | Michigan State University Extension. Facts About Soil Acidity and Lime (E1566). https://www.canr.msu.edu/resources/facts_about_soil_acidity_and_lime_e1566 |
[6] | NC State Extension. Soil Acidity and Liming: Basic Information for Farmers and Gardeners. https://content.ces.ncsu.edu/soil-acidity-and-liming-basic-information-for-farmers-and-gardeners |
[7] | Penn State Extension. Soil Acidity and Aglime. https://extension.psu.edu/soil-acidity-and-aglime |
[8] | Mississippi State University Extension. Effects of Liming Materials on Soil pH. https://extension.msstate.edu/newsletters/forage-news/2023/effects-liming-materials-soil-ph |
[9] | Penn State Extension. High Tunnel Soil Test Report: Soil Nutrient Levels. https://extension.psu.edu/high-tunnel-soil-test-report-soil-nutrient-levels |
[10] | Purdue University Vegetable Crops Hotline. Basic Aspects of High Tunnel Soil Fertility Management. https://vegcropshotline.org/article/basic-aspects-of-high-tunnel-soil-fertility-management/ |
[11] | Purdue University Vegetable Crops Hotline. High Tunnel Soil Fertility Management: What You Need to Know. https://vegcropshotline.org/article/high-tunnel-soil-fertility-management-what-you-need-to-know/ |
[12] | Bayer Vegetables. Soil Health in High Tunnel Systems. https://www.vegetables.bayer.com/us/en-us/resources/growing-tips-and-innovation-articles/agronomic-spotlights/soil-health-in-high-tunnel-systems.html |
[13] | UMass Amherst – New England Vegetable Management Guide. Phosphorus, Potassium, Calcium, and Magnesium. https://nevegetable.org/cultural-practices/Phosphorus-Potassium-Calcium-Magnesium |
[14] | eOrganic / Oregon State University. High Soil Test P and K Levels on a Long-Term Organic Farm. https://eorganic.org/node/20735 |
[15] | ScienceDirect / Soil & Tillage Research. Lime and gypsum application to low-acidity soils: Changes in soil chemical properties (2023). https://www.sciencedirect.com/science/article/abs/pii/S0167198723002271 |
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Q: What is the ideal soil pH for growing superhot peppers?
A: University extension research from Minnesota, Michigan State, and UMass consistently recommends a soil pH of 6.0–6.8 for Capsicum chinense and related species, with 6.5 often cited as the optimum. Our own three-year dataset at Harmony Springs Farm confirms this: the strongest pre-plant baseline we've ever recorded was pH 6.18 in March 2026, achieved after incorporating 360 pounds of dolomitic limestone per UTK Extension guidance. Below pH 6.0, nutrient availability — particularly phosphorus — is suppressed even when soil reserves are rated High.
Q: Why does soil pH drop in a high tunnel?
A: High tunnels exclude rainfall, which prevents the natural leaching of acidic compounds from the root zone. Combined with intensive production under nitrogen-based fertility programs (nitrogen forms like ammonium acidify the soil as they nitrify), pH drops season-over-season without active correction. Our high tunnel soil dropped from pH 6.16 (November 2023) to pH 5.22 (November 2025) over two production seasons — a 0.94-unit decline — before we implemented a structured lime management program in consultation with UTK Cooperative Extension.
Q: How much dolomitic lime is needed to raise pH in a high tunnel?
A: Application rates depend on your current pH, buffer pH, and target pH. Our UTK Extension representative recommended 360 pounds of dolomitic limestone for our specific soil conditions. The critical factor we learned firsthand: surface-applied lime must be incorporated by tilling to affect subsurface pH. Our back-to-back tests in March 2026 — one before tilling, one after — recorded a 0.60-unit pH difference from the same lime application. Penn State Extension confirms this: lime incorporation through tillage significantly accelerates pH correction through the soil profile.
Q: Is high soil phosphorus a problem for superhot pepper production?
A: High phosphorus is common in intensively managed high tunnel soils and, while it rarely causes direct toxicity, it warrants monitoring. Penn State Extension's survey of 27 high tunnels found that 96% had phosphorus levels exceeding crop needs. Our own P values rose from a Low rating of 18 ppm at our 2023 baseline to a High of 97 ppm by March 2026. As a result, we're planning no additional phosphorus inputs for the 2026 season. Importantly, phosphorus availability is maximized between pH 6.2–7.2 — another reason correcting our pH from the mid-5s to 6.18 unlocks nutrients already present in the soil.
Q: Does Harmony Springs Farm publish its soil test data?
A: Yes. This post represents our complete longitudinal soil dataset from November 2023 through March 2026 — six tests from the same growing zone, all conducted by the University of Tennessee Extension soil testing laboratory. Lab numbers for each test are cited in Section 10 and original reports are retained on file. We publish this data because process transparency is a core value at the farm, and because we believe the specialty pepper community benefits from growers sharing real numbers, not just growing advice.
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