Exomad Green Corn and Bean Field Study
Study note on “Biochar Field Study — Corn and Beans in Controlled Plots”, a 13-page field report published by Exomad Green and run with CIAT (Centro de Investigación Agrícola Tropical) at three sites in Santa Cruz, Bolivia. Biochar was applied once at 4 t ha⁻¹ before a winter bean crop (2024); corn followed with no re-application (PDF). Exomad accounts for roughly 60% of biochar CDR tonnes sold since 2022 (CDR.fyi Snapshot 2025); this is one of the field-study PDFs on its R&D page. Report context: 2026-09-14.
Related notes: Crop Yield Effects · Real World Soil Projects · Soil and Agriculture · Application Rates and Methods · Biochar Inoculation for Fertilizer · Biochar Microbes and Soil Biology · Supply Landscape · Applications Hub · Key Sources
Bottom line
- Headline gains (as reported): biochar alone +15% corn and +13% beans; biochar + NPKS + microorganisms +32% corn and +25% beans vs an untreated control (PDF p.8; p.10). Direction fits meta-analyses of low-fertility tropical soils (compares tropical vs temperate yields · DOI).
- Yield differences are not statistically significant. The report’s own ANOVA gives yield p = 0.4481 (beans) and p = 0.924 (corn). Only bean plant height (p < 0.0001) and corn 100-grain weight (p = 0.014) differ significantly (same pages).
- Only T2 vs T1 isolates biochar. There is no fertilizer-only arm, so the larger T3/T4 gains cannot be credited to biochar.
- Bean percentages are understated. Against the control, beans gain +14.9% / +24.9% / +34.2% (T2/T3/T4), not the printed 12.94 / 19.90 / 25.47% — the report divided by treatment yield instead of control yield (§6.1).
- Soil-health conclusions come without soil data. Better nutrient availability, porosity, moisture retention, leaching, CEC, and pH are asserted (PDF p.13), but no post-trial soil tests are shown.
- Use it as supportive company case evidence with these caveats attached — not as proof of a yield response.
1. Study at a glance
| Item | Detail | Source |
|---|---|---|
| Publisher | Exomad Green — in-house, not peer-reviewed; CEO Diego Justiniano called it “this latest study by our team” | PDF p.1 · Bioenergy International |
| Partner | CIAT — Santa Cruz departmental agricultural research center (not the Colombia-based CGIAR CIAT); runs the Cañada Larga and Saavedra experimental stations, a Mairana regional center, and a soil–water–plant laboratory | PDF p.3 · ciatbo.org |
| Sites | CL Cañada Larga, Chiquitania (map label: Pailón EECL) · EEAS Saavedra experimental station, Northern Zone · CRI Mairana regional research center, Valleys | PDF p.3–4 |
| Design | Four treatments (§2). Layout figure shows 16 plots (4 × 4), each treatment once per row and column; site shown, replicates per site, plot size, and statistical model not stated | PDF p.5 |
| Biochar dose | 4 t ha⁻¹ once, manual & mechanical, 30 days before bean planting; dry vs as-received basis not stated | PDF p.6 |
| Crop sequence | Beans (winter; planted June 2024) → corn (summer) after bean harvest, no additional biochar | PDF p.6 · p.13 |
| Weather | ”Severe drought” stated on the corn results page; no rainfall or irrigation data | PDF p.11 |
| Published | Undated PDF; press coverage 2025-07-04 (§9) | Carbon Herald |
| Files | Canonical exomadgreen.com PDF · same file on Wix’s file host (filesusr link); SHA-256 identical (checked 2026-09-14) | — |
2. Treatments
| Code | Treatment (as printed) | Adds vs previous arm |
|---|---|---|
| T1 | Control (no intervention) | — |
| T2 | Single application of biochar without microorganisms | Raw biochar |
| T3 | Biochar + NPKS fertilizers | + fertilizer |
| T4 | Biochar + NPKS + microorganisms | + microbial inoculant |
Source: PDF p.5. Exomad says its biochar is “usually activated” with microbes including Rhizobium, Pseudomonas, Azospirillum, and mycorrhizae (PDF p.2); the T4 inoculant’s product, dose, and timing are not given.
Missing arms: fertilizer only, microbes only, and fertilizer + microbes without biochar. For contrast, meta-analyzes yields with fertilizer controls measure the ~+15% biochar effect against fertilizer alone (PDF) — the comparison this design cannot make.
3. Biochar used (as reported)
| Parameter | Value | Benchmark |
|---|---|---|
| Organic carbon | 86.3% | NRCS CPS 336 requires C_org > 10% (CPS 336 PDF · defines NRCS practice 336) |
| H:C_org | 0.24 | Under the 0.7 limit in the IUPAC definition and NRCS (IUPAC biochar terminology · DOI); under Isometric soil < 0.5 (module) and CSI ≤ 0.40 for GPC (CSI 3.3) |
| Ash | 8.6% | — |
| pH | 7.2 | Near-neutral; NRCS notes biochar is usually alkaline and valued for liming acid soils — liming equivalence not reported (NRCS FAQ · answers CPS 336 planning questions) |
| Moisture | 18% | Dose basis matters (below) |
Values: PDF p.2. Not reported: feedstock, pyrolysis temperature, particle size, lab or method, sampling date, or whether H:C_org is molar. Exomad’s Concepción facility listing describes sawmill hardwood residues pyrolyzed at ~600 °C (Puro facility page), but the report doesn’t say which facility supplied the trial char. Persistence context: biochars with H/C_org < 0.5 retained a mean ~82% of C after 100 years in reviews biochar climate mitigation (DOI) — see Permanence and Properties.
Applied carbon (vault arithmetic, not a credit figure): 4 t ha⁻¹ × 86.3% C ≈ 3.45 t C ≈ 12.7 t CO₂ ha⁻¹ gross if the dose is dry-basis; ≈ 2.83 t C ≈ 10.4 t CO₂ ha⁻¹ if it is as-received at 18% moisture. Credited tonnes apply persistence factors and life-cycle deductions — Puro Biochar Methodology Edition 2025, Permanence Science for Credits.
4. Site soils (baseline, CIAT lab)
| Parameter | Units | CRI (Mairana) | CL (Cañada Larga) | EEAS (Saavedra) |
|---|---|---|---|---|
| pH (H₂O) | – | 6.08 | 6.4 | 6.3 |
| CEC | cmolc kg⁻¹ | 6.54 | 10.1 | 4.9 |
| N | % | 0.04 | 0.18 | 0.1 |
| P | ppm | 16 | 47 | 18 |
| K | meq 100 g⁻¹ | 0.21 | 0.17 | 0.18 |
| Organic matter | % | 1.08 | 2.8 | 1.7 |
| Sand / clay / silt | % | 76 / 22 / 2 | 21 / 61 / 19 | 49 / 16 / 35 |
| Texture (printed) | – | LSC | CL | LS |
| USDA class from printed fractions (vault check) | – | sandy clay loam | clay | loam |
Source: PDF p.4 (CIAT Water, Soil and Plant Laboratory). Sampling depth and date are not given. CL fractions sum to 101%. The printed texture codes don’t match the USDA triangle for CL (61% clay is “clay”) or EEAS (“LS” usually means loamy sand; 49/35/16 sand/silt/clay is loam), so treat the codes as unverified.
Reading: CRI and EEAS are mildly acidic, low-OM, low-CEC soils — the tropical low-fertility setting where meta-analyses report larger yield responses (Jeffery 2017; meta-analyzes crop productivity · DOI). CL is a high-clay, higher-P soil. Results are not broken out by site, so these contrasts can’t be tested from the report.
5. Agronomy by crop
| Item | Beans | Corn |
|---|---|---|
| Biochar | 4 t ha⁻¹, 30 d before planting | None added (residual from bean season) |
| Planting date (as printed) | Jun 2 (CRI), Jun 5 (EEAS), Jun 20 (CL) 2024 | Nov 24 (EEAS), Dec 8 (CL) 2023; Jan 2 (CRI) 2024 — see §8 |
| Row spacing | 20 cm | 45 cm |
| Seed | 50 kg ha⁻¹ | 20 kg ha⁻¹ |
| Crop cycle | 110–120 d | 120–130 d |
| P₂O₅ / K₂O / SO₄ | 18.32 / 66 / 15 kg ha⁻¹ | ”Applied with bean crops” (no new P/K/S) |
| Zn–B–Cu | 1 L ha⁻¹ | — |
| N | N/A | 100 kg ha⁻¹ |
Source: PDF p.6. The fertilizer rows presumably apply only to the fertilized arms (T3/T4); the table doesn’t say.
6. Results
6.1 Beans (harvest)
| Treatment | Height (cm) | Flowers | Yield (kg ha⁻¹) | Δ vs T1 (kg ha⁻¹) | % vs T1 (recomputed) | % printed |
|---|---|---|---|---|---|---|
| T1 Control | 44.55 | 21.60 | 1,189.10 | — | — | — |
| T2 Biochar | 47.05 | 22.30 | 1,365.94 | +176.84 | +14.9% | +12.94% |
| T3 + NPKS | 51.58 | 24.40 | 1,484.66 | +295.56 | +24.9% | +19.90% |
| T4 + NPKS + microbes | 56.98 | 25.15 | 1,595.48 | +406.38 | +34.2% | +25.47% |
| CV % | 17.32 | 28.9 | 23.47 | |||
| ANOVA p | < 0.0001 | 0.3002 | 0.4481 |
Source: PDF p.8. Each printed percentage equals (T − T1) ÷ T, not ÷ T1. The 58-day “preliminary assessment” lists T1–T4 with blank descriptions and shows one photographed plant per treatment (PDF p.7).
6.2 Corn (harvest; drought season, no new biochar)
| Treatment | Height (cm) | 100-grain weight (g) | Yield (kg ha⁻¹) | Δ vs T1 (kg ha⁻¹) | % vs T1 (printed ≈ recomputed) |
|---|---|---|---|---|---|
| T1 Control | 156 | 24.5 | 1,962.27 | — | — |
| T2 Biochar | 165 | 27.5 | 2,249.90 | +287.63 | +14.7% |
| T3 + NPKS | 169 | 29.0 | 2,259.11 | +296.84 | +15.1% |
| T4 + NPKS + microbes | 128 | 30.5 | 2,590.67 | +628.40 | +32.0% |
| CV % | 7.95 | 7.9 | 57.49 | ||
| ANOVA p | ”<0.44” (as printed) | 0.014 | 0.924 |
Source: PDF p.10; ear photo and drought statement on p.11. T4 plants were ~18% shorter than the control yet highest-yielding; the report doesn’t explain why. A 57.49% yield CV implies a residual SD of ~1,300 kg ha⁻¹ on a ~2,270 kg ha⁻¹ mean (vault arithmetic) — consistent with site or drought variation left in the error term, but the model isn’t described.
6.3 What each contrast isolates (vault arithmetic from table means)
| Contrast | Isolates | Beans | Corn |
|---|---|---|---|
| T2 − T1 | Raw biochar | +176.8 kg ha⁻¹ (+14.9%) | +287.6 (+14.7%) — second-season residual |
| T3 − T2 | NPKS fertilizer, given biochar | +118.7 (+8.7%) | +9.2 (+0.4%) |
| T4 − T3 | Microbial inoculant, given biochar + NPKS | +110.8 (+7.5%) | +331.6 (+14.7%) |
| T3 − T1 | Biochar + NPKS combined (no fertilizer-only arm to split them) | +295.6 (+24.9%) | +296.8 (+15.1%) |
| T4 − T1 | Whole package | +406.4 (+34.2%) | +628.4 (+32.0%) |
No yield difference is backed by a significant ANOVA in either crop (§6.1–6.2). In corn, 100 kg N ha⁻¹ added almost nothing on top of biochar (T3 vs T2 +0.4%). That would fit water rather than nutrients limiting a drought season, but the report gives no rainfall or soil-moisture data to check.
7. How it fits the vault’s evidence
| Question | This study | Wider evidence |
|---|---|---|
| Does raw biochar raise yields? | +15% in both crops, not significant | Tropical mean ~+25% (Jeffery 2017); grand mean ~+10% (Jeffery 2011); +9.4% (global GHG and yield patterns · DOI) → Crop Yield Effects |
| Did uncharged char cause yield drag? | No sign in T2 (numerically positive) | NRCS warns fresh char can immobilize nutrients and reduce yields (FAQ) → Biochar Inoculation for Fertilizer |
| Do microbes add value? | T4 − T3: +7.5% beans, +14.7% corn; inoculant unspecified | Inocula beat biochar alone on average, but commercial products are weak and field effects are smaller than greenhouse (Ross & Emery meta · meta-analyzes microbial inocula) → Biochar Microbes and Soil Biology |
| Is 4 t ha⁻¹ a typical rate? | One 4 t ha⁻¹ dose carried into a second crop | Research trials often ~5–50+ t ha⁻¹ (Jeffery 2011); enriched biochar fertilizers often < 2 t ha⁻¹ (liquid nutrient enrichment trials · DOI) → Application Rates and Methods |
| Drought resilience? | Claimed for corn; no water data | Largest water-retention gains in coarse soils — FC +23.8% / AWC +25.6% (Wei 2023); AWC +15.1% overall (Omondi 2016) → Soil and Agriculture |
| Does it pay? | No costs or revenue reported; Exomad donates char to local communities (Puro facility page) | → Agronomic Economics |
| Credit relevance | Not a credit document; yield effects don’t enter CORC quantification | Exomad’s CORCs rest on soil end-use and persistence (Puro facility page) → Supply Landscape · Puro Biochar Methodology Edition 2025 · Real World Soil Projects (credit project ≠ agronomic trial) |
8. Data-quality issues
- Non-significant yields (beans p = 0.4481; corn p = 0.924), with no mean-separation tests; replication, plot size, and statistical model undescribed (PDF p.8; p.10).
- Confounded treatments — no fertilizer-only or microbes-only arms (§2).
- Mixed percentage bases — beans ÷ treatment, corn ÷ control (§6.1). Press coverage repeated the understated bean figures (Bioenergy International; Carbon Herald).
- Date conflict — corn is printed as planted Nov 2023–Jan 2024, before the June 2024 bean crop it followed. June planting + 110–120 days puts bean harvest around late Sep–mid Oct 2024, so Nov 2024–Jan 2025 is the likely intent — unconfirmed (PDF p.6).
- Charts disagree with tables — e.g., corn 100-grain-weight bars read ≈19 / 28 / 37 / 37 g against 24.5 / 27.5 / 29.0 / 30.5 g in the table (PDF p.12 vs p.10); bean flower bars also drift (p.9). Use table values.
- Soil-health claims without data — no post-trial pH, CEC, OM, bulk density, or moisture measurements (PDF p.13).
- Not reported — per-site results, bean species or variety, corn hybrid, incorporation depth, particle size, inoculant product and dose, weather, yield moisture basis.
- Conflict of interest — a producer and credit seller reporting its own trial; CIAT is named as collaborator, but no CIAT authors, sign-off, or raw data appear in the PDF.
9. Press coverage and related Exomad material
| Item | Date | Notes | URL |
|---|---|---|---|
| Bioenergy International | 2025-07-04 | Headline figures (corn +15% / +32%; beans +13% / +25%), drought, CEO quote; links the PDF | https://bioenergyinternational.com/biochar-field-study-reveals-significant-crop-yield-improvements-in-bolivia/ |
| Carbon Herald | 2025-07-04 | Same figures; no CIAT mention or statistics | https://carbonherald.com/in-a-new-field-study-exomad-green-finds-biochar-improved-corn-and-bean-crops/ |
| farming.co.uk — AGROVIDAS soil-health plot | 2025-08-28 | A different Exomad demonstration (fair-field site); don’t merge with this trial | https://farming.co.uk/news/exomad-greens-biochar-field-study-demonstrates-transformative-soil-health-improvements |
| Exomad R&D page | — | Lists this study with Exomad’s other field-study PDFs | https://www.exomadgreen.com/research-development |
| Exomad — sorghum under arid conditions (not yet summarized) | — | Yacuiba, Tarija (Chaco); 6.15 t ha⁻¹ on 1.3 ha; slightly alkaline, grazing-compacted soil (pH 7.5) | https://www.exomadgreen.com/_files/ugd/8b0a69_9e7dd73d46d84e33aa86b7a7308c14b2.pdf |
| Exomad — La Rivera (not yet summarized) | 2023–24 season | La Rivera farm, Concepción (Santa Cruz); degraded acidic soil (pH 5.2) with untreated control sections; billed as the first of 20+ Exomad field studies | https://www.exomadgreen.com/_files/ugd/8b0a69_89a6513212434da5af5a2734956a6a3c.pdf |
Related notes
- Evidence: Crop Yield Effects · Real World Soil Projects · Soil and Agriculture
- Practice: Application Rates and Methods · Biochar Inoculation for Fertilizer · Biochar Microbes and Soil Biology · Biochar Nutrients and Fertilizer Chemistry · Agronomic Economics
- Char quality & persistence: Properties · Permanence · Permanence Science for Credits
- Exomad in markets: Supply Landscape · Historical Deals · Buyers and Offtakes · Puro Biochar Methodology Edition 2025
- Navigation: Applications Hub · Key Sources · Biochar Home