Final report for LNE22-452R
Project Information
Biochar has been widely proposed as a soil amendment based on its large surface area, porosity, and durability characteristics that may influence habitats for beneficial microbes, intrinsic water-holding capacity, soil health, and carbon storage. Because biochar can be produced from local biomass waste streams, it has been promoted as an accessible renewable resource. Biochar has also been promoted as a potential mechanism for capturing and storing carbon and mitigating extreme weather events. It has been studied in annual systems, but less often in the perennial context of tree crops, particularly in temperate climates.
Farmers have expressed interest in biochar as a potential tool, but adoption remains limited due to high costs and uncertainty about its utility and a lack of information and data showing its efficacy in similar agricultural systems. This project was designed to address these uncertainties by conducting a field-based biochar trial in a chestnut agroforestry system under realistic management conditions and a detailed scientific literature review of biochar’s efficacy in agriculture. We also documented our exploration of the scientific research and agricultural use of biochar in our region through a video documentary.
The field research component of the project was located at Arthur’s Point Farm in New York’s Hudson Valley. We applied five treatments to 120 chestnut trees across three planting rows during the initial planting and on an annual basis thereafter, using locally-produced, lab-tested biochar from sustainably-sourced wood. We analyzed 60 individual trees divided into 20 experimental units, replicating each treatment four times. The research sought to isolate the effects of straight biochar, straight compost, biochar mixed with compost, and biochar mixed with compost and amended with a mix of micronutrients, minerals, and microbes ("amendment").
We hypothesized a “synergistic” effect by the introduction of compost with biochar, combined with additional organisms and related nutrients intended to "inoculate" the biochar-compost, and that this would produce measurable changes in soil properties and/or tree performance relative to standard biochar-alone or compost-based management. The hypothesized changes were expected to include increased soil organic matter, retained soil carbon, altered microorganism abundance, altered plant uptake of nutrients, and generally positive traits of the growth and productivity of the subject chestnut trees.
The results of the Chestnut research trial found that the biochar treatment did not measurably influence any single or combined plant or soil trait over four years. We concluded that biochar had no detectable effect within this agroforestry system. Compost emerged as primary driver of plant and soil responses. The compost-biochar-amendment treatment was not statistically distinguishable from the compost treatment, indicating that inoculation had no additional synergistic effect. Notably, high field-level variability reduced the power to resolve treatment effects. However, even with lower variability, the direction and magnitude of the responses suggest the overall conclusion would likely remain unchanged.
Our scientific literature review provided several key findings. First, the biochar origin theory that posits ancient dark earth soils such as Terra Preta in the Amazon were anthropic in nature has been challenged with a competing theory that geomorphic forces may have also contributed to the creation of these soils. Regarding agronomic responses to biochar, we found highly variable reports for: positive, neutral, or negative effects, depending on soils, fertility, crops, and biochar used. We also found few long-term field studies, particularly in temperate soils focused on agricultural systems similar to those found in the 
northeastern United States. Many reported trials rely on pots or unusually high application rates. There is high variability in the chemistry, structure and potential agronomic effects based on biochar feedstock and production process, but little practical guidance for tailoring materials to field conditions. Co-composting or post-mixing can create surface coatings, yet evidence for consistent biological or agronomic synergy is limited. Biochar's high cost compared with other established soil and plant health practices like compost, cover cropping, diverse crop rotations, and the addition of perennial crops necessitates clearly diagnosed soil limitations, defined objectives, and field-verified responses to justify broad adoption by farmers in the 
region. Benefits are highly dependent on the entire lifecycle of production and use, including the biomass feedstock, pyrolysis technology, and field application, which need to be analyzed and verified to determine whether they provide net greenhouse gas emissions reductions or not.
We communicated these findings to our Farmer Working Group and communicated with additional farmers, biochar producers, and scientists as part of our video documentary. Our findings will be published on our website and promoted through social media channels and professional networks. We intend to present our findings at scientific and relevant agricultural meetings and conferences throughout 2026. We hope this research assists growers, researchers, and funders to continue targeted research and development on the production and use of biochar that are guided by realistic expectations, site-specific needs, and a clear understanding of both its potential and limitations.
Interest in biochar is increasing as a means of enhancing long-term soil fertility and carbon storage. A lack of data and farmer experience related to biochar’s benefits and optimal management practices, especially regarding tree crops, is a significant constraint on broader adoption. This project aims to quantify the relationship between inoculated biochar and chestnut trees to provide farmers with a regenerative tool to increase crop vigor and yield. With growing interest in chestnut agroforestry in the Northeast, this project comes at an opportune time for farmers establishing new orchards and for future regional studies with biochar and other tree crops.
Cooperators
- (Researcher)
Research
Biochar Field Research
The field research component of the project was located at Arthur’s Point Farm in New York’s Hudson Valley. The field, which has been used for hay, orchard, and pasture for most of the past two centuries, is hilly with Nassau channery silt loam, primarily composed of silt particles with a large volume of small rocks. The research was conducted on three 800-foot rows that transect the field and are planted with hybrid Chestnuts (Castanea spp.) and Black locust (Robinia psuedoacacia) alternated at 10-foot spacing and 20 feet between rows. The trees were planted in 2022, the first year of the research project. The project was laid out as a 4x replicated study. For practical reasons the treatments were laid out non-randomized in order of treatment, across the length of the field.
Hypotheses
- That biochar combined with compost and a microbial amendment (Treatment 5 below) would positively effect beneficial soil microorganism abundance, nutrient bioavailability, tree health and vigor, and carbon capture/storage potential.
- That the native soil control (Treatment 1) would perform relatively worse that the compost and biochar treatments across assessment metrics.
- That the biochar control (Treatment 2) would negatively effect beneficial soil microorganism abundance, nutrient bioavailability, and tree health compared with the treatments containing compost and biochar (Treatments 3-5).
Treatments
The biochar used in this study was produced at Arthur's Point Farm using a low temperature pyrolysis (~450℃) thermochemical conversion in an Exeter retort kiln using a mix of hardwood and softwood from sustainably sourced trees and scrap wood from a neighboring lumber mill. The compost was produced from a mixture of livestock manures and animal bedding from a nearby farm. Biochar-compost is created by adding biochar to the compost mix at the start of the composting process.
Treatment 1 (T1): Hybrid Chestnut (Castanea spp.) and Black locust (Robinia pseudoacacia) trees planted into native soil. This treatment represented the most commonly employed method of planting chestnuts. Planting into native soil provided a control for the other treatments.
Treatment 2 (T2): Four cups of raw biochar mixed with native soil in the planting hole. T2 analyzed how biochar reacts with native soil unaccompanied by introduced microbial life.
Treatment 3 (T3): One gallon of compost mixed with native soil in planting holes, top-dressed annually with two gallons of compost. T3 tested the benefits of an accessible and commonly used soil amendment and controls for the effects of compost in the biochar treatments.
Treatment 4 (T4): One gallon of compost and four cups of biochar mixed with native soil in planting holes, top dressed annually with two gallons of biochar-compost. T4 is distinguished from T3 by the addition of biochar, both in the planting hole and mixed into annual top dressings.
Treatment 5 (T5): One gallon of compost, four cups of biochar, and four cups of an amendment of micronutrients, minerals, and beneficial microbes (“amendment”) mixed with native soil in planting holes, top-dressed annually with two gallons of biochar-compost. The amendment consists of alfalfa meal, oat meal, kelp meal, azomite, and a consortia of soil bacteria (sourced from Advancing Eco Agriculture): Arthrobacter globiformis; Azospirillum brasilense; A. lipoferum; Azotobacter chroococum; A. paspali ; A. vinelandii; Bacillus amyloliquefaciens; B. atrophaeus; B. Licheniformis; B. megaterium; B. pumilus; B. subtilis; Brevibacillus brevis; Micrococcus luteus; Pseudomonas fluorescens; P. putida; Rhodopseudomonas palustris; Rhodospirillum rubrum; Streptomyces griseus; and soil mycorrhizae: Glomus intraradices; G. deserticola; G. etunicatum; G. clarum; G. claroideum; G. mosseae; Gigaspora albida.
Treatment 3 received an annual top-dressing of compost and Treatments 4 and 5 received an annual top-dressing of a 10:90 biochar:compost blend. Annual top-dressing applications occured in the spring, starting in the planting year (2022). Hand-weeding was performed as needed. Application rates were based on typical quantities recommended by leading biochar products. All trees in the five treatments are mulched annually with 10 gallons of wood chips.
Experimental Design
Sampling and Analysis
Soil samples were taken in April of 2022, 2024, and 2025 with a 3/4-inch diameter auger-corer, to a depth of 6” ( 0 - 15 cm). This soil sampling happened semi-radially around the first chestnut in each experimental unit on each of the three rows (See Figure 3, Soil Sampling Design). The sampling circle had a radius of approximately two and a half feet from the tree. We did not collect data in 2023 as a cost-saving measure and allow us to do a fuller suite of tests in 2024 and 2025 (growing seasons 3 and 4 of the project).
Soil samples taken from around the study trees were all analyzed for agronomic nutrients and soil health indicators. Separately, on fresh undried samples and only on 2 occasions (2022 and 2025) samples were split for microbial abundance analysis by a proprietary substrate utilization assay (Vitellus, A&L Labs, Canada). This microbial abundance method consists of the measurement of 17 soil microbial functional groups by semi-quantitative color reduction assay. From this array, relationship indices are calculated (such as total fungi:total bacteria or gram-negative:gram-positive bacteria). This method has not been published.
The group of indicator tests comprising the “Nexus” soil health test, (Woods End Labs) included potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), storage phosphorus (P), Solvita CO2-burst, Solvita labile amino-nitrogen (SLAN), a volumetric aggregate stability test (VAST), nitrate, soil organic matter, pH, C:N ratio, and lab bulk density (BD). The soil health index is calculated from 9 individual tests indexed against ideal values. The overall fertility score is calculated as a 50/50 combination of the soil health scores plus a separate scoring of sufficiency of nutrients (NO3, N-min, P-tot, P-sol, K-exch, P-extr). pH is not used in this scoring. Information of the soil health procedure from peer-review papers is found in the appendix.
To assess nutrient bioavailability, leaves were collected from a combination of the six chestnut trees in each experimental unit in August 2022, August 2024 and in the final year, 2025) and shipped fresh in paper bags to Woods End Research Farm, Mt Vernon, Maine for sample during and preparation. Following this they were ground and analyzed for total-nitrogen, phosphorus, potassium, magnesium, calcium, sodium, sulfur, boron, zinc, manganese, iron, copper, and aluminum. We also calculate the molar ration of K : (Ca + Mg) as an indicator of cation balance.
Tree health and vigor was assessed by applying standard tree assessment protocols adapted from the Forest Ecology Monitoring Cooperative, a partnership between the University of Vermont, the New York DEC, and the Forest Service. Data were collected on live crown ratio, vigor, dieback, foliage transparency, defoliation, and foliage discoloration. Tree health and vigor were evaluated in August 2024 and assessed again in 2025.
Deep carbon core samples were taken on two occasions, in March 2022 and March 2025 to a target depth of 1-meter or to the rejection layer, whichever came first. The average depth attained was 77 cm (30”). The coring device was a self-powered a Geoprobe 54DT hydraulic rig. After extraction of the core in a PVC inner tube, the tube was transported to the prep lab (Woods End Farm, Mt Vernon Maine). Of this deep core, the tube was cut to produce two carbon samples (0-0.15 m (6”), and the remaining balance (nominally 0.16-0.77 m). The cores were taken in the drive aisles between the tree rows, five feet above and below the central row, for a total of 40 samples. All samples were air
dried, stones sieved and analyzed for total organic carbon and bulk density, where the density is the dry weight of soil minus stones within the sample volume of the tube. The carbon stock was calculated by correcting soil density at depth. Unfortunately, the soil lab (Woods End Laboratory, Augusta ME) changed the standard operating procedure (SOP) for soil density core sampling after the first year of study. This had to do with how to deal with the high content of stone gravelin the samples, which pose a problem to labs. As a result, we were unable to meaningfully compare year-4 data with year-1 data with respect of changes in carbon stock per hectare, while still having accurate measures of baseline data for BD and TOC.
Data was analyzed using licensed version 22.4 Minitab Statistical software (State College, PA) combining basic statistics including normalization, analysis of variance (ANOVA) and correlation regressions.
Farmer Working Group Satellite Research
The ten Farmer Working Group participants were each asked to replicate the research treatments on their respective home farms and were provided with five chestnuts and five black locusts, along with all the materials necessary to apply the research treatments. Each farmer was asked to make visual observation on the health and growth rate of their trees and report back to the research team. Due to budget limitations and logistical challenges, the research was not designed to collect soil samples for these small satellite trials. The farmer observations have been documented in a survey form that follows the same protocol we will use in assessing tree health and vigor at the main research site at Arthur’s Point Farm. Three of the farm participants did not complete these tasks for different reasons - either because they did not manage to plant the research trees or neglected to care for them - and were no longer participating in the satellite trials or the Farmer Working Group.
The value of the Farmer Working Group was more from the opportunity to educate a group of farm professionals in our region on the nature of the research and the potential for biochar as a soil amendment and for mitigating fluctuating weather conditions. The interactions with the farmers allowed us to share research results and obtain feedback and questions from a real-world perspective. The visual survey information they collected did not provide usable information in our research project due to the sample sizes and overall variability at each farm, we feel that the practice of planting a replicate of the experimental design enabled them to fully understand what we were testing and increased their engagement with learning about our research results. The outreach we conducted with farmers and researcher for the documentary video we created, further expanded the outreach and our network of farmers with interest in biochar, which we plan to continue to communicate with in the future. We feel that these relationships will assist us in communicating the results and conclusions of the research to an even broader audience throughout the region and beyond.
Biochar Scientific Literature Review
Our review was motivated by knowledge gaps in the scientific literature and a lack of detailed, proven best practices for growers. The review evaluates the current scientific evidence of biochar’s efficacy as an agricultural amendment and a potential mechanism for mitigating fluctuating weather conditions. The paper was based on a literature search and retrieval process supported by the digital libraries of University of Maine and Unity Environmental College. The database search tool Publish or Perish (Harzing, 2007) was used to sort and identify papers in categories by frequency of citation. The AI research tool Semantic Scholar (Allen Institute for AI, 2025) was used to list papers including, but not limited to, the following keywords: biochar, charcoal, phytotoxicity, crop yield, field study, pot study, N2O emissions, nitrate loss, cation exchange capacity, ammonium retention and environmental remediation. Boolean operators AND, OR were used, where appropriate, to select for crop studies.
Additional use was made of the program Crossref (2025), with tools for metadata integrity checks and author cross referencing. For critiquing of analytical statistic methodology employed in selected papers, we employed Minitab Statistical Software (2017) with its AI-supported Hypothesis Analysis, Reliability Analysis, Sample Size check tool, and Measurement System Analysis, the latter a tool that examines design appropriateness for reported objectives. We chose to limit ourselves to about 100 peer-review published papers. Our initial search found 1,000 relevant papers published in the past 20 years in each category of “biochar” or “compost.” The top 100 papers focused on compost (main keyword with Boolean AND Crop) revealed 35,193 citations (i.e., in other peer-reviewed papers) and the top 100 papers for biochar as keyword revealed 71,183 citations, as of November 30, 2025.
The purpose of the review was to clarify the conditions under which biochar may offer benefits and to highlight knowledge gaps that call for additional research. Our intent was to assist researchers, growers, and funders in interpreting the current evidence base so that future study and use of biochar are guided by realistic expectations, site-specific needs, and a clear understanding of both its potential advantages and limitations.
Biochar Field Research
The research results are presented in the SARE Biochar Field Research Results presentation and discussed below. Research data also can be accessed below.
Tree Health and Vigor
Tree health and vigor were measured through scoring and scaling six attributes (height, crown, live crown ratio, vigor, dieback and discoloration) according to the protocol developed by the Forest Ecology Monitoring Cooperative, a partnership between the University of Vermont, the New York DEC, and the Forest Service. Tree physiological traits were also compared by regression analysis to tissue tests conducted at each interval. Additionally, we were concerned about how tree replacement might have affected results. Due to random, sporadic tree mortality, certain tree locations were replaced by replanting with new, younger stock. We assessed if frequency of replacement of trees caused a non-uniform trend for our overall data. There was no observed change in physiological or mineral test traits apart from boron in tissue, which was deflected downwards significantly by sampling younger leaves from replacement trees (Slide 21).
Overall results showed that desirable tree performances most closely corresponded to more tissue nitrogen (N) and potassium (K) and potassium most closely correlated to compost alone amendment. Thus, 2022 performance correlated with crown height in 2024. (Figs. Slide 15). All FEMC tree physiological indicators were highly inter-correlated (Slide 20); for example, Tree Vigor correlated strongly and negatively to leaf discoloration which in turn was highly correlated to tree leaf tissue nitrogen. Most tree tissue minerals were closely cross-correlated, such as N:K:P:S, yielding strong evidence of a nutritional food-chain that favored compost as the principal driving force, and biochar alone ranked mostly as low or sometime lower than the controls, and amended biochar (combinations with compost and probiotic) generally in between, but not distinguished from compost alone. (Slides 15 – 21).
Overall tree height gain over the 4-year time frame was evaluated by treatment. On average trees gained height exponentially from as baseline of 15 inches to 25 and 35”, respectively for Controls from Yr3 and Yr4 measures, to the largest gain of 15 -> 25 -> 45” in the case of compost treatments. Biochar alone treatments were no different than controls. Using Yr3 and Yr4 data for height, (Slide 17) compost was significantly greater than the controls and the full spectrum amendment with biochar and probiotic, which is curious. This alone strongly supports a null conclusion, that biochar supplementation did not improve results but worsened them. One theory is that this may result from two factors: dilution of amendment by the high-porosity biochar (biochar was ¼ the density of other treatments) and the fact that the probiotic was microbially very active material and may have cause nutrient immobilization once placed in the raw soil. This latter hypothesis remains untested. The overall finding is that using tree physiological parameters we can only clearly state that compost significantly improved quality traits compared to the control, and we failed to be able to distinguish biochar combinations from these – sometimes they were positive and sometimes negative trends, but not statistically appreciable.
Soil Health
Baseline soil results in 2022 determined that there was a very large difference in soil layers, comparing topsoil to the remainder depth to about 30”. Apparent bulk density (BD) was 1.443 and 1.876 g/cc for 0-0.15 m and 0.16-0.60 m, respectively. The corrected bulk density (g/cc) after stone removal was 1.095 and 1.121 for 0-0.15 m and 0.16-0.77 m depth, respectively at the project start. Shale stones comprised a significant proportion of our samples. In the final year (2025) the BD values for screened soils were not significantly different from baseline values at 1.13 and 1.07 g / cc, respectively, for topsoil and subsoil. However, using raw BD samples, all layers and all years differed significantly from each other. This indicated that without careful stone removal and quantitation, the correction to carbon stock (carbon per acre) will be strongly challenged by methodology.
The field overall fertility score ranged at the end of the study from the lowest of 49% (biochar) to the highest of 56% in the compost treated soil (Slide 30). Only the compost was significantly different from the control; all other treatments could not be distinguished as being different from the control and conversely, they could be distinguished from the compost.
The soil health index averaged 22 (arbitrary units on a 0–50 scale) across all treatments in the baseline year (2022) and declined significantly to 18 by year four. Among the treatments, compost was the only amendment that did not exhibit a statistically significant decline, decreasing from an index value of 20 to 18. Biochar-treated plots showed the largest decline in soil health index over time, although this decline was not statistically different from the untreated control (Slide 29). A likely explanation for these results is that soil amendments were applied only within localized planting zones, whereas soil sampling encompassed a broader area. As a result, measured responses would reflect only indirect effects extending beyond the amended zones, such as nutrient diffusion, root-mediated transport, or surface litter inputs, rather than direct amendment effects. This sampling mismatch likely reduced the sensitivity of the soil health index to treatment differences.
In retrospect, treating the entire sampling area—including the inter-row sward—would likely have improved overall soil condition and increased the ability to detect treatment effects. However, such an approach would have represented a different management system rather than a test of localized tree establishment amendments. Future studies evaluating biochar or compost in agroforestry systems may benefit from explicitly aligning amendment placement with soil sampling design or from testing whole-system management strategies separately from localized interventions.
Several specific aspects of nutrient chemistry relationships are notable. Of 1,034 unique pairs of test data for 60 soil samples examined by comparing soil health, mineral nutrients and microbiological levels using Pairwise Pearson Correlation analysis at 95% C.I. we found that twenty four pairs showed some level of statistical importance (>95% certainty, p < 0.05). Of these only 4 pairs showed positive interactions, while 20 had negative correlation meaning that one variable is adversely affected by the other. Furthermore, for instance, higher levels of pH are linked to reduced microbiology. Higher levels of K, Ca, Mg affected microbe utilization negatively with a certainty of 99% (p<0.01). (Figs. Slide 14)
Elevated soil pH and increased concentrations of base cations (Ca, K, and Mg) are commonly observed following applications of biochar and compost; however, compost also supplies organic nitrogen, which biochar does not. When examining soil phosphorus (using two extraction methods), exchangeable potassium, calcium, magnesium, and soil pH in this study, the dominant driver of observed changes was the presence of compost. In most cases, compost alone was not significantly different from biochar + compost or biochar + compost + probiotic treatments.
Soils at the study site were initially low in potassium. Compost applications increased exchangeable potassium to approximately 53 mg kg⁻¹ (= ppm), whereas the control and biochar-only treatments remained at 36–37 mg kg⁻¹, a level considered deficient. These results indicate that the site can be characterized as potassium-limited, where amendments supplying potassium would be expected to produce measurable soil responses. While positive soil responses to biochar have been reported in nutrient-depleted soils, the biochar used in this study did not contain elevated potassium relative to the compost or compost-based treatments and therefore did not independently contribute to potassium enrichment.
The cation balance results give a more inclusive, “holistic” result since this is an molar ration index of potassium to Ca + Mg. In this case, once again, compost significantly out-performed control and biochar which were the lowest, and statistically the amended biochars were not distinguished in between. This supports our overall conclusion that use of biochar would not be chosen “ideally” but by careful pre-analysis of the soil conditions and biochar quality to match the potential nutrient needs of the intended crop, in this case trees. In Slide 20 we can see that potassium played a crucial role correlating significantly positively with height and crown and strongly negatively (a good result) with discoloration. Testing pH completes this analysis. In our samples, pH increased significantly across the entire field over time (from 6.17 to 6.53)(Slide 28). In this case the highest soil pH occurred with the combined treatment (Compost+ Biochar+ Probiotic) as compared to the biochar alone, which was the lowest, and all other treatments were in between. These effects are attributable principally to calcium loading from the organic amendments.
Carbon Content and Stock
Two forms of analysis are used to assess soil carbon: one is gravimetric or total weight-based analysis of soil total organic carbon and the other is analyzing in relationship to soil volume density to arrive at the stock per acre (or hectare). The analysis for TOC is straightforward since it depends only on the sample itself; the Stock depends on the volume density which is a more complicated measure with its own source of error, especially due to the required correction of stone content.
When analyzing total organic carbon (TOC) we found substantial differences, depending on the depth of analysis, as expected. Average starting TOC in core samples (0-0.15 m) was 1.32% ± 0.34 %, (1.26% ± 0.38 % in fertility samples), whilst in the deeper layer TOC measured only 0.19% ± 0.11% - values close to zero.
In the baseline year, 2022, there was a very high correlation between the fertility samples of 0 – 15 cm (0 – 6”) and the deep core samples for the 0 – 15 cm topsoil sample with regard to TOC content. Since these analyses are prepared from separately sampled methods, this high degree of correspondence suggest the area is well and accurately characterized.
If the baseline data is used to calculated carbon stocks (soil organic carbon, SOC) at 0 - 0.15 m (0 to 6”) we found 17 t ha-1, representing about 60% of total profile carbon, while at the entire remainder soil depth contained additionally 11 t ha-. These data can be used to estimate changes over time at future sampling points, but also suggest the effort and cost to sample beyond the 6” (0 – 15 cm) layer, may not be worthwhile.
In the final year sampling (2025), the overall field TOC was identical to the original control plot samples (Slide 23) or 1.34% C ± 0.40 vs 1.34 ± 0.26 at the start. The treatment with the highest TOC in the final year was Compost+Biochar+Probiotic (Slide 23). This treatment also had the largest addition rate of organic matter and carbon (see Slide 8).
Carbon comparisons in TOC % between 2022 and 2025 showed close correlation, (R2 = 0.3463 P < 0.05 between Yr 1 and Yr3), but with a significant dip in the second sampling period. There was large variance across the field and within replicates (Slide 22). Variability is controlled in statistics and normalization procedures but nevertheless, reduces the ability to distinguish treatment effects with confidence. Based on the visual graph, all treatments with compost increased in TOC by Yr4, but the Control and Biochar did not, with no significance to the observed differences.
Field Research Report & Data
Final SARE Biochar Field Research Results LNE22-452R
2025 Data
2025 Soil Health and Fertility Report
2025 Visual Observations Data All Years
2025 Total Carbon Macro-Core Data
2024 Data
2024 Soil Health and Fertility Report
2022 (Baseline) Data
2022 Total Carbon Macro-core Data
Biochar Scientific Literature Review
The complete Literature Review can be accessed here. Excepts from the paper are included here, with the citations excluded for clarity. Please refer to the paper for complete information.
Scientific research on biochar has grown rapidly over the past two decades—by some estimates outpacing related fields such as compost science. This surge of activity has fostered the perception that sufficient knowledge exists to justify widespread adoption, especially as an agricultural amendment. Yet the evidence remains mixed and context dependent.
Numerous studies have reported improvements in soil properties—such as water retention, aggregation, or nutrient retention—and in some cases increases in crop productivity or plant use efficiency. However, virtually all these reported benefits are highly variable across sites and study designs, and several well-controlled trials have documented neutral or even suppressive effects on plant growth or reduced nutrient availability. Meta-analyses further indicate that positive yield responses are largely confined to degraded, nutrient-poor tropical soils, and are rarely expressed in temperate systems. These conflicting results raise fundamental questions about when, where, and why agricultural benefits of biochar may occur.
Biochar also has been recognized as a natural solution that can capture/store carbon from renewable biomass sources and offset the use of fossil fuels with the surplus energy created during pyrolysis. Studies have also shown that biochar can reduce emissions of methane, nitrous oxide, and ammonia – significant sources of greenhouse gas emissions and environmental pollutants – from livestock operations and other nitrogen-intensive systems. These benefits are dependent on the entire lifecycle of production and use, including the biomass feedstock, pyrolysis technology, and field application, which need to be analyzed and verified to determine whether they provide net greenhouse gas emissions reductions or not.
The real-world costs and benefits of biochar for agriculture and to mitigate fluctuating weather conditions are dependent on many variables: feedstock, pyrolytic production process, agricultural conditions, plant needs, crop type, planting system, inoculation process, application rates, energy use, and carbon capture/storage potential. Addressing these uncertainties requires substantial continued work in agronomy, plant-soil interactions, and rigorous life-cycle evaluation of greenhouse-gas impacts across diverse production pathways. Equally important is research into whether and under what specific conditions commercial-scale systems are economically justified or environmentally beneficial given the variability of outcomes and alternative amendments available for soil and plant health.
Health risks to workers and communities exposed to biochar production and application are underexplored, particularly the potential for exposure to polycyclic aromatic hydrocarbons (PAHs), which are known mutagens and carcinogens emitted or retained during pyrolysis. Concerns about PFAS (per- and polyfluoroalkyl substances) contamination of farmland and water supplies from sewage-sludge field applications also raises questions about whether biochar made from such “biosolids” can be done safely and responsibly.
The evidence reviewed here indicates that key scientific and practical questions about biochar’s agronomic efficacy, safety, environmental sustainability, and economic viability remain unresolved. Until these questions are fully addressed, prescriptive recommendations for widespread or routine application are not justified. Recommendations for biochar use should remain targeted and evidence-based, rather than generalized, and should be paired with simple, field-based feedback that allow farmers and land managers to observe outcomes from real-world application and adjust practices as more empirical evidence emerges.
Biochar has been promoted as a rare “win–win” intervention, simultaneously improving soil health while delivering durable mitigation of fluctuating weather conditions through carbon capture/storage. However, the evidence from this project indicates that both claims are context-dependent and highly variable across biochar types, production processes, applications, growing-zones, soil types, and agricultural systems.
Biochar Field Research Conclusions
The results from our field research project found that biochar treatments did not measurably influence any single or combined plant or soil trait over four years. We conclude that biochar had no detectable effect within this chestnut agroforestry system. Compost emerged as the primary driver of plant and soil responses in our study. Compost+ Biochar+Probiotic Amendment (Treatment 5) effects were not statistically distinguishable from the Compost Treatment alone, proving that inoculation had no additional synergistic effect in this case. It is important to note that field-level variability was high and reduced the power to resolve treatment effects. However, even with lower variability, the direction and magnitude of the responses suggest the overall conclusion would likely have remain unchanged.
Our specific critiques of the field study include the challenge faced by the undulating landscape, which prevented field uniformity and reduced the ability to accurately distinguish non-random effects. The confinement of treatments (biochar, compost etc.) to a relatively small area around the trees limited holistic and interactive observations which might have emerged had we applied treatments field wide. We observed a general decline in soil health during the project due to large untreated areas suggest growers should not confine amendments to desired spots. Reduced treatments would have improved efficiency, since literature does not support distinguishing highly “nuanced” effects. The reliability of the deep carbon sampling was challenged by interference from stones and how the labs handled this. If this kind of sampling is repeated in the future, we recommend that the USDA-Kellog method 3B6* should be used for analyzing deep cores.
Scientific Literature Review Conclusions
Across annual crops, orchards, prairies, and forest systems, a substantial body of literature documents that biochar can measurably alter soil chemical and physical indicators, including pH, water-holding capacity, nutrient concentrations, and total carbon. However, the evidence reviewed here reveals that mechanical or chemical soil changes do not reliably translate into consistent improvements in crop yield, plant performance, or ecosystem function across soil types, regions, or management systems. In perennial and ecologically complex systems, these indicator shifts have rarely been found to result in demonstrable restoration of biological function. This broad finding was in line with the results of our biochar-chestnut field study, which found that compost had a more significant effect on soil health and plant growth than biochar.
Where positive responses are reported they are more closely attributable to co-applied composts, fertilizers, liming effects, or nutrient-rich feedstocks, rather than to biochar itself. The strongest agronomic effects of biochar documented in the scientific literature occur under the following conditions: acidic, nutrient-poor, or degraded soils; applications of alkaline or nutrient-enriched biochar; treatments combined with fertilizer or organic amendments; and short-term and highly controlled experiments. In fertile soils, temperate regions, perennial systems, or biologically constrained situations, biochar has been reported to provide little or no measurable agronomic benefit, and in some cases, produces negative outcomes. These patterns indicate that biochar’s agricultural value is highly conditional rather than generalizable.
Our review detected recurring structural tendencies in the biochar literature that have contributed to an overly optimistic portrayal of biochar’s agronomic potential. These include inadequate control structures (especially nutrient- and pH-matched controls), reliance on short-term pot and laboratory studies, statistical shortcuts that obscure variability, and the routine conflation of mechanical or chemical soil shifts with soil health, restoration, or functional improvement. Importantly, these limitations are not confined to primary studies that we reviewed but are frequently propagated, and amplified, through meta-analyses and higher-order syntheses. By aggregating heterogeneous experiments with uneven controls, short durations, and context-specific responses, such analyses often obscure the constraints present in the underlying primary studies while reinforcing positive summary estimates. As a result, tentative or conditional findings from individual studies are routinely presented downstream as robust or broadly applicable conclusions. Aggregation of studies, in this context, does not resolve uncertainty; it often compresses and masks it.
Together, these patterns suggest that caution is warranted when interpreting summarized evidence concerning biochar and its effects. Moreover, we find that much greater attention to experimental design, control structure, and functional validation is necessary to avoid perpetuating conclusions that exceed the strength of the original data.
Claims that biochar directly enhances soil microbial communities or their functions warrant particular caution. Across many studies reviewed, biological responses are commonly inferred from indirect indicators, short-term assays, or mechanistic plausibility rather than demonstrated microbial persistence, functional integration, or plant response. In most cases, biochar is applied in combination with composts, fertilizers, or microbial products, making it difficult to distinguish biochar-specific biological effects from nutrient- or pH-driven responses. Visual evidence from electron microscopy of microbial attachment to biochar surfaces has frequently been treated as functional proof, despite the absence of data demonstrating sustained colonization, competitive advantage, or ecological relevance. The evidence base for biochar as a broad soil or ecosystem restorative agent remains speculative and claims of its agronomic or ecological utility should be interpreted with caution and context specificity.
Biochar’s potential as a natural solution is also highly context-dependent, conditional on the net GHG emissions reductions from the entire lifecycle of feedstock production, processing, and use. Recalcitrance and persistence in soil are essential to assessing benefits and the long-term fate of biochar carbon in soil remains poorly constrained, with persistence inferred largely from structural proxies in the lab rather than measured decay dynamics. By highlighting these limitations constructively, we aim to provide clarity for land managers, researchers, and funders and to help guide future research toward designs and applications that are empirically defensible, context-specific, and proportionate to demonstrated benefits.
Education & outreach activities and participation summary
Educational activities:
Participation summary:
At the outset of this project, we conducted a survey of northeastern farmers to gauge interest in biochar’s potential as a soil amendment or conditioning. The survey showed broad interest among farmers who had heard of biochar, but hesitancy to use it due to a lack of information and data. This study sought to facilitate farmer engagement by convening a Farmer Working Group of 10 farmers to implement a small-scale trial of the five research treatments on their own farms. As part of the outreach conducted for the biochar video documentary, we visited several farms involved in biochar research projects or applying biochar experimentally with support from the USDA NRCS. Over the duration of the project, Farmer Working Group members attended two workshops (one in person and one virtual) to learn about biochar and the specific research undertook as part of this project, and to learn the results of our field-based and literature-based research. The farmers we met with provided feedback and perspective on the current opportunities and constraints for broader adoption of biochar as a soil amendment on farms in the Northeast.
We conducted an inaugural workshop with the Farm Working Group and collaborating research scientists in March of 2022 (slide presentation). We provided an overview of biochar and described the details of the research being conducted at Arthur's Point and the sample trials that the Working Group members are undertaking on their home farms. We toured the farm and showed the farmers how we currently make and use biochar. We had in-depth discussions about various related topics and then provided the farmers with their research kits (5 chestnut and 5 black locust seedlings, biochar, compost, soil amendment, tree tubes, weed mats, and written instructions). In late 2022, we sent an update to the Farmer Working Group on the research and outreach efforts. We also conducted one-on-one meetings with the three Farmer Advisory Group members.
We presented on the use of biochar and compost on a 2022 Connecticut Compost Webinar Series hosted by the CT Department of Resource Conservation & Development in March of 2022 with over 100 attendees. This presentation included an overview of the SARE project (video recording here).
We also published a blog on our website announcing the launch of the project as well as another blog promoting a bill in Congress that would create a national biochar research network. We discussed our use of biochar with the local USDA Natural Resource Conservation Service extension office during a visit to the farm this past summer. We discussed the newly established soil practice for biochar and was told that they hope to begin offering payment for services through CRP in 2023.
In addition, we hosted two workshops in 2022 with substantial focusses on biochar, including the SARE project work, one for the Berkshire Botanical Garden and the other for the Climate Farm School (presentation).
The SARE research project was also referenced in a report by the American Farmland Trust, the National Center for Appropriate Technology, and the Foundation for Food & Agriculture Research entitled "Scaling Sustainable Biochar Research Commercialization for Agriculture Conservation," published in December of 2022.
In December of 2022, we were interviewed for the Nature Calls podcast, focusing on agroforestry, biochar, and ecological resilience. The episode can be accessed here.
In September of 2022, 2023, and 2024 Arthur's Point Farm participated in the Chatham Area Farm Tour, which brought over 50 visitors to the farm each year. Participants were shown the biochar production process on the farm and were given an overview of the SARE research project. In 2022 and 2024, Arthur's Point Farm helped to organize the Columbia County Climate Carnival.
Significant time in the Fall-Winter of 2024-2025 was spent networking with scientists, biochar producers, researchers, and farmers in the region. The primary purpose of this work was to promote our research and to assess other activities and projects in the region. The second purpose was to plan interviews and site visits for the biochar video documentary we produced as part of this project.
Individual calls with the three Farmer Advisors reviewing the first year's work and discussing ways in which we can continue to engage farmers. Field visits to Farmer Working Group and Advisers in spring of 2023 and 2024 to provide trial amendments, replacement trees, and to give an update on the project.
We plan to use the literature review and the results of our field study to submit a manuscript for a peer-reviewed journal article. Extracts of the research will be digested and incorporated on our website and in future blog articles.
Relevant findings may be presented at conferences, such as the Savannah Institute’s North American Agroforestry Conference, Northern Nut Growers Association Annual Meeting, and the Northeast Organic Farmers Association.
These products will help farmers, extension services, NRCS service providers and policy makers across the region to better understand the linkages between biochar and other organic amendments, soil health, and tree crop vitality and productivity.
Learning Outcomes
The practical potential of biochar in agriculture and land restoration warrants greater caution than is commonly conveyed in online forums and the popular literature. We entered this study heavily influenced by preconceived notions of biochar's broad efficacy for enhancing soil and plant health. Based on the overwhelmingly positive information online, in popular literature, and in the scientific papers we had read, we honestly believed that we would demonstrate how beneficial biochar was in our soils and temperate agricultural systems. Only after completing our field research and the in-depth scientific literature review (both done as scientifically and objectively as possible), as well as from visiting and learning from farmers and researchers in the region, we have a much more nuanced understanding of the field. We are now in a position to bring this knowledge to a broader audience of farmers, extension officers, researchers, funders, and the general public. We plan to continue this effort with the tools and research we have developed as part of this project.
The clearest finding from our review is that biochar’s effects are highly context-dependent and, in many cases, weak or negligible unless specific soil constraints are present. Where positive outcomes have been reported, they are associated with chemistry changes to the soil such as pH increases, added nutrients like potassium and calcium from residual ash, or improved water retention in coarse soils, rather than due to unique biological or purported ecosystem-restorative functions of biochar itself.
Consequently, applying biochar without a clear diagnosis of the underlying soil limitations, and without comparison to available alternatives, can result in limited measurable benefits and occasionally negative agronomic or environmental outcomes. This result or pattern is reinforced by methodological features common to the literature we examined, including relying on short-term pot experiments, incomplete factorial designs, indirect biological indicators, and meta-analyses that synthesize or aggregate results without fully accounting for limitations inherent to the original studies. Taken together, the evidence from examining the literature does not currently support biochar as a broadly applicable solution for improving soil health, enhancing productivity, or restoring ecosystem function. Additional field research is needed with well-designed studies comparing different biochar amendments with organic and conventional treatments across a range of crops and farm systems analogous to the ones where it is being considered for use. Continued research is also needed to determine direct agronomic and soil health effects of biochar amendments under real world conditions over multiple growing seasons. Biochar production systems must also be further evaluated for life-cycle greenhouse gas emission reductions and health and safety effects to ensure broad claims of environmental sustainability are accurate and transparently communicated in the commercial marketplace. Absent conclusive evidence of biochar’s context-specific agronomic benefits, verified environmental sustainability, and clear cost-effectiveness compared with current agricultural practices, we conclude that biochar should be regarded as an experimental amendment, appropriate only under well-defined conditions and with realistic expectations about its likely effects.
Practical Considerations
Comparing Soil Constraints and Biochar Type
Taken together, the literature does not support biochar as a broadly applicable soil improvement strategy. Where benefits have been reported, they are conditional on aligning biochar type and blending and application protocols with existing soil constraints. A precautionary, diagnostic approach – grounded in soil constraints, realistic application rates, and verification in analogous climate-growing zones and agricultural systems – is therefore essential.
- Biochar responses reported as positive are concentrated in soils that are acidic, nutrient-poor, structurally degraded, or otherwise chemically constrained, particularly in tropical or highly weathered systems.
- If soils already exhibit adequate pH, organic matter, nutrient availability, and aggregation – as is common in many temperate agricultural and perennial systems – the literature reviewed here suggests that biochar is unlikely to improve productivity and may, in some cases, suppress plant performance.
- Most biochars will raise pH in acidic soils, but this is a liming effect rather than a unique biochar benefit – and may be achieved more cheaply with traditional liming materials. It is relatively easy to have an agricultural lab test performed for lime requirement, although the WBC analysis certificate does not list a “lime equivalent” procedure (WBC, 2023).
- Manure-based and low-temperature biochars contain more plant-available nutrients than wood-based biochars, but these benefits reflect nutrient addition, not the biochar’s structure. Always first evaluate the amount of nutrients required and then determine the amount of manure or biochar manure that would be required to meet those needs. It is questionable that a biochar alone can supply sufficient major crop nutrients (N, P, K, Ca, Mg, S) without exceeding an economic sustainability threshold.
- Use biochar sparingly if at all in seedling growing media since the germination and early development of seedlings relies on a moderately acid soil reaction (generally pH 6.2). If mixing biochar with peat, coir or leaf-mold, pre-test the resulting blend pH (which should be < 6.5) before using it as a general growing media.
Compost and Fertilizer Blending and Application
- “Raw” biochar has been reported in limited studies to temporarily adsorb nutrients (g., ammonium) from soil or fertilizers. The effect usually occurs at very high rates and without supplemental nutrients. Since ammonium is present in soil normally in very low amounts, this restriction should be carefully evaluated.
- Claims of biochar–compost synergies usually reflect compost or nutrient additions and surface coating of biochar, not a unique biological effect of biochar.
- Blending or co-composting biochar can reduce some nutrient losses (g., nitrate), but the dominant effects generally reflect the compost or fertilizer – not the biochar itself. It is best to assess how and why nutrient leaching would be present in the first place.
- Positive yield effects reported in trials generally occur only when biochar is added along with fertilizer or compost; biochar alone rarely has a yield effect or may reduce yield. Assess whether a higher result is needed and what the cost to obtain it would be to augment with biochar.
Understanding the Characteristics and Genesis of Biochar Before Use
- Obtain laboratory analysis, preferably independent of the biochar manufacturer, detailing feedstock, pyrolysis temperature, ash content and chemistry factors (pH, C, Ca, Mg, K, P, B, S), electrical conductivity, and potential contaminants such as PAH – rather than relying on generic descriptions.
- Interpret biochar properties in relation to specific diagnosed soil constraints in your situation (e.g., soil pH, texture, salinity, organic matter), recognizing that biochar properties must match a specific need; otherwise, little or no benefit should be expected. For example, plant-based biochar often has higher ash content than wood-based biochar and therefore carry more mineral-ash residue that may bolster yields under depleted circumstances.
- Consider logistical and economic factors—application rate, cost per nutrient unit, transport, and handling—as very high rates used in research trials (> 5% of growing media or in the range of 5–25 t/a) are rarely practical or cost-effective on farms.
Project Outcomes
This project clarified that, despite rapid growth in scientific and commercial interest, biochar should not be treated as a universally effective soil amendment. While biochar is often promoted as a broadly proven tool for improving soil health and mitigating fluctuating weather conditions, the research reviewed and synthesized through this project demonstrates that its performance is highly variable and strongly context dependent.
The project confirmed that biochar can improve certain soil properties—such as water retention, soil structure, or nutrient dynamics—under specific conditions. In some cases, these changes are associated with improved crop performance or nutrient-use efficiency. However, these benefits are inconsistent. Outcomes vary widely depending on soil type, growing zone, crop species, biochar feedstock, production method, and application practices. Importantly, well-controlled field trials have shown that biochar can also produce neutral or negative effects, including reduced plant growth or nutrient availability.
Synthesis of existing studies indicates that positive yield responses are most consistently observed in highly degraded, nutrient-poor tropical soils. In temperate agricultural systems similar to those in the Northeast region, yield benefits are far less predictable and often absent. This finding highlights a critical knowledge gap regarding when and where biochar is agronomically justified in regional farming systems.
The project also evaluated claims about biochar as a strategy to mitigate fluctuating weather conditions. While biochar has the theoretical potential to capture/store carbon and reduce emissions of methane, nitrous oxide, and ammonia in certain systems, these benefits are not inherent to biochar itself. Instead, they depend on full life-cycle factors, including biomass source, pyrolysis technology, energy inputs, transportation, and field application. Without rigorous life-cycle accounting, claims of net greenhouse gas reductions remain uncertain.
Economic and practical feasibility emerged as equally important considerations. The costs and benefits of biochar depend on many interacting variables, including feedstock availability, production scale, application rates, inoculation practices, and compatibility with existing farming systems. This project underscores that commercial-scale biochar systems are not inherently cost-effective or environmentally beneficial and must be evaluated against alternative soil health strategies on a case-by-case basis.
The project also identified significant gaps related to safety and risk. Health impacts associated with biochar production and application—particularly exposure to polycyclic aromatic hydrocarbons (PAHs)—remain underexplored. Additional concerns exist around biochar derived from sewage sludge or biosolids, especially regarding potential PFAS contamination and long-term impacts on soil and water quality.
Overall, this project concluded that key questions regarding biochar’s agronomic effectiveness, environmental performance, economic viability, and safety remain unresolved. As a result, broad or prescriptive recommendations for biochar use are not supported by current evidence. Instead, outcomes from this project support a targeted, cautious, and evidence-based approach to biochar adoption—one that is grounded in local conditions, transparent evaluation, and on-farm observation. This approach aligns with SARE’s emphasis on adaptive management, farmer learning, and practical decision-making informed by real-world results rather than generalized claims.
Information Products
- Biochar Agroforestry Research Project Launched
- Farmer Working Group - Inaugural Workshop Presentation - The Use of Biochar in Agroforestry to Promote Soil Microbial Health, Tree Productivity, and Carbon Sequestration
- Climate Farm School Training Presentation - Agroforestry, Biochar & Climate Resilient Farming