Improving nutrient retention with biochar

Final Report for GS10-093

Project Type: Graduate Student
Funds awarded in 2010: $9,852.00
Projected End Date: 12/31/2012
Grant Recipient: University of Florida
Region: Southern
State: Florida
Graduate Student:
Major Professor:
Dr. Danielle Treadwell
University of Florida
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Project Information


A series of short experiments to assess plant response to the same biochar source produced at different temperatures and applied at different rates determined that the rate of application was more important than temperature of generation, but results were inconclusive regarding the optimum rate of application in the field. Biochar made primarily from white pine chips was manufactured on campus in a laboratory setting at approximately 400 ºF and 800 ºF, and was applied to a series of pot and field experiments at rates ranging from and . Biochar remains an expensive input with limited commercial availability. The continued characterization of physical and chemical characteristics of commercial biochar and studies of plant response to application strategies will assist farmers interested in evaluating benefits in situ.


The purpose of this project was to investigate the effects of biochar amendments on nutrient and water retention and crop productivity. The potential for nutrient leaching to the ground water is very high in the sandy and calcareous soils of Florida. Fertilizer expenses consume 20% of Florida pepper growers’ and 22% of tomato grower’s pre-harvest variable costs (VanSickle 2009), and are typically the highest pre-harvest expense for growers. Nitrogen and phosphorous lost as runoff or leachate is a major economic loss and source of environmental pollution (Barbarick, 2006). In sandy soils under conditions of high rainfall or high irrigation, studies indicate that up to 33% of nitrogen fertilizer can be lost as leachate (Nyamangara et al. 2003). However, biochar has been shown to contribute significantly to nutrient retention in soils (Lehmann, 2003; Steiner, 2008). Our hypothesis was that by combining biochar and common soil amendments, a superior product will be created (in the sense of nutrient retention, water-retention, CEC capacity, increased soil microbial life, etc.) that surpasses the qualities that compost, biochar, or organic fertilizer could provide on their own. Thus, the biochar-compost will reduce leaching of irrigation water, and increase the stability and retention of various nutrients, and provide those nutrients to plants as a slow-release fertilizer and in bio-available forms.

Over the past few years, convincing evidence has become available that biochar is not only more stable than other amendments, and that it increases nutrient availability, but that these basic properties of stability and capacity to hold nutrients are fundamentally more effective than those of other organic matter in the soil – and therefore biochar is more efficient at enhancing soil quality than any other organic soil amendment (Lehmann and Joseph, 2009). Yet aside from one recent study by Rillig et al (2010), limited research has been done to test the effectiveness of biochar produced by hydrothermal carbonization in the context of plant growth, and no studies to date have been preformed with this type of biochar in conjunction with additional soil amendments. According to the International Biochar Initiative (established at the 2006 World Soil Science Congress), biochar is one of the few technologies that is relatively inexpensive, widely applicable, and quickly scalable. At least ten commercial biochar production facilities are in operation globally (and one major producer in the southeast region of the United States, Eprida) are already producing and marketing biochar, and therefore the opportunity is ripe to study its effects in agronomic systems and its economic viability.

Our working hypothesis was that adding biochar-compost to various farming systems will help to mitigate the economic problems associated with the loss and inefficient capture of nutrients, as well as to reduce the overall irrigation needs of various crops. In the future, should carbon-credits or tax breaks be offered for carbon sequestration, then biochar-compost could offer further financial benefits to farmers.

This project was inspired by the Terra preta soils that have been studied in the Amazon region. These soils were created by indigenous peoples thousands of years ago, and have maintained high levels of organic matter, high nutrient levels, and high microbial and fungal life. The natural soils in this area have very low organic matter, very low nutrient retention. However, thousands of years after their creation, the Terra preta soils are being harvested for use as potting mix and compost. Since charcoal is one of the primary ingredients thought to lead to Terra preta formation, in essence, one of our project’s long-term goals is attempting to recreate these types of soils through use of biochar-compost. This project has implications for sustainable management of agricultural waste products, as well as mitigation of global climate change (through carbon sequestration, as biochar has been shown to exhibit high stability in the magnitude of hundreds to thousands of years). Moreover, the byproducts of the biochar production process can be harnessed as renewable energy sources, and then used to power various farm machinery and energy needs.

Biochar technologies have the potential to simultaneously provide a renewable energy source, serve as valuable soil conditioner, address problems of waste management, and mitigate problems of global climate change (Lehmann and Joseph, 2009). Therefore, an opportunity exists to determine appropriate management strategies for on-farm implementation of biochar, for optimizing biochar performance, and for further understanding biochar’s effects on soil fertility and sustainable crop production.

Currently, biochar research is underway at at least twenty-five universities around the world, including Cornell, University of Georgia, and Iowa State University. Additionally, there are approximately twenty-five networks and organizations around the world working to advance knowledge and dissemination of knowledge related to biochar (i.e, Rodale Institute, UK Biochar Research Center). At least fifty companies are working on biochar-related technology, and approximately ten of those companies are currently offering biochar for commercial sale (Eprida, Best Pyrolysis Inc, Carbon-Char, etc.). The current scientific knowledge on bichar was recently compiled by two eminent biochar scholars, Dr. Johann Lehmann of Cornell University and Dr. Stephen Joseph of the University of New South Wales, and published as Biochar for Environmental Management: Science and Technology.

Our proposed research will provide information with immediate applicability for vegetable growers in the Southeast region who have an interest in using biochar in their operations. Our findings will establish baseline data for horticultural crop applications in the sandy soils of the southeastern coastal plain. The long term goal is to develop overall best management practices (loading rates, biochar types, application method) for biochar additions to vegetable cropping systems in varying soil types.

Project Objectives:

The goal of this project was to increase nutrient retention, crop productivity, and soil quality by adding biochar in various management contexts, and to compare various application rates and biochar-compost, biochar-manure, and biochar-fertilizer combinations. Specifically, the objectives were to:

1. Evaluate biochar + “amendment” combinations in a greenhouse setting in regards to nutrient retention, nutrient availability, soil moisture retention and crop productivity. Establish the precise parameters for future field trials, in regards to biochar application rate and amendment quantities.
2. Prepare and deliver outreach to inform growers, the public, and scientific audiences of results of research.


Click linked name(s) to expand
  • Seth Friedman


Materials and methods:

All experiments used the biochar produced from white pine chips sourced from the same lumber company and made using a pyrolizer designed by Dr. Green, Professor Emeritus, University of Florida, at approximately 800 ºF. Sufficient biochar was manufactured over a period of one week to use in all experiments below. Procedures were as follows:
Conduct Standard Toxity Tests on Biochar. Three 1.5 gallon trays were filled with field soil collected from the top 6 inches of the student teaching farm on the University of Florida campus. Soil collected from production areas but had not recieved any amendments for the past three months. Trays were divided in half with cardboard, and treated in three ways: 1) without biochar/without biochar; 2) biochar/biochar; and 3) without biochar/biochar. Biochar sides each received .25 lbs of biochar (mixed together with soil in bucket prior to placement in trays). Each side was screened for removal of debris, pre-moistened with equal amount of water, and twenty red wiggler worms were deposited in middle of each tray. After forty-eight hours, two pieces of cardboard were placed in center two-three inches of each tray to partition off the center aisle. The center aisle of each tray was not counted. In each side, worms were counted. Any worms crushed by the cardboard were not counted. The experiment was repeated immediately after with new soil, biochar, and worms.

Conduct Germination Tests. Three trays were filled with field soil as previously described, and amended with biochar as follows: 1) without biochar; 2) low rate of biochar + soil; and 3) high rate of biochar + soil. Trays were arranged randomly in each block and replicated three times. The low rate of biochar treatment received 5% char by volume, and the high rate of biochar received 15% (by volume). As in the worm test, the soil was screened for removal of debris. For uniform distribution, the soil was mixed with proper quantities of biochar prior to addition to containers. Prior to seeding, the containers were pre-moistened with 50 mL water. Placement of treatment/controls were randomized within each block. Fifteen lettuce seeds were sown in each container (three lines of five seeds). After six days, experiment was concluded and total germination for each tray was counted, for each block. For soil moisture assessment, prior to commencing the trial, soil in container was dried and weighed. During trial, regardless of soil moisture, water was applied at rate of ten sprays (20 mL) per day per container. At days two, four, and six, water leachate was assessed (weighed) from each container in each block.

Conduct Greenhouse Trial. A pot trial was established in March in a greenhouse at the University of Florida’s main campus in Gainesville with the following treatments: control (untreated soil only), fertilizer + soil, biochar + fertilizer + soil, manure + fertilizer + soil, compost + fertilizer + soil, biochar + manure + fertilizer + soil, biochar + compost + fertilizer + soil. Treatments were arranged in randomized complete block design. The biochar was thoroughly mixed with Arredondo series (well-drained, fine sand, 1.5% OM) soil extracted from the top 6” from a previously managed but fallow field at the UF-IFAS Plant Science and Education Unit in Citra, Florida. The mixture was tested in 8” pots at the following biochar application rates: 0%, 15%, 30%, and 60% (vol:vol). The purpose of applying biochar at low, medium, and high rates was to extrapolate approximate recommended loading rates for field trials. To avoid confounding effects of germination, butterhead lettuce (cv. Rex) was transplanted into pots at six weeks. Monitoring was performed to quantify leachate, soil moisture (continuous monitoring with a HOBO data logger), and plant vigor (visual rating). Fresh and dried plant biomass (shoot and root) was assessed at termination. Soil quality indices (soil total nitrogen, soil inorganic nitrogen, extractable phosphorous, and soil pH) were collected three times during the trial. Data were analyzed using GLM and least significant differences were determined with Fisher’s Protected LSD (SAS V.9, Cary, NC).

Research results and discussion:

After conducting standard toxicity tests (germination and worm) on the biochar, initial trials indicated that the biochar was suitable (non-toxic) for further testing. Our results indicated that there were no differences in which sides of the tray that the worms preferred (biochar/non-biochar) and the lettuce seeds had improved germination at the higher biochar rates versus the control and lower biochar rates. The next phase of research included an evaluation of the material in a controlled environment to determine soil solution nitrogen concentration and water holding capacity of soil when biochar was added at different rates.
Lettuce performed poorly in biochar only treatments, and rate of fertilizer was more important than rate of biochar to lettuce growth and development. Head diameter achieved a maximum of 7.0 inches in biochar + fertilizer treatments prior to showing signs of stress approximately 45 days after seeding. A delay in planting lettuce coincided with above average daily temperatures in early spring and reduced plant vigor overall. A shade cloth was installed over the experimental area inside the greenhouse to reduce heat and solar radiation, and was successful in reducing plant stress. Total soil nitrogen content was greatest in treatments receiving fertilizer (P< .0001), but all other comparisons of soil N were not significant for any of the sample dates evaluated. There were no interactions among rate of biochar application, fertility application or temperature of biochar manufacture for any of the parameters measured. Data loggers were used to measure soil moisture and temperature. Soil moisture ranged from 5% to 15% (field capacity for Arrendondo soil series is 17%) but no differences were attributed to the presence of biochar. Similarly, soil temperatures fluctuated diurnally and ranged from 65F at night to 91 F during the day. High soil temperatures likely contributed to reduced lettuce productivity. Lettuce heads were cut at soil level, dried and weighed at harvest. Biochar plus fertilizer treatments were 15% greater than fertilizer alone, but not statistically different. Overall, data from the greenhouse trial were extremely variable and it was difficult to data observations to treatment effects.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Prior to beginning the research, Mr. Friedman attended the National Biochar Conference in Ames, Iowa, and learned about the latest developments in biochar research. In addition, Mr. Friedman delivered a forty-five minute lecture to over 400 undergraduate students enrolled in FRC101 “Growing Fruit for Fun and Profit” at the University of Florida on the topic of organic/sustainable crop production, and offered an emphasis on sustainable soil management strategies and cited examples of farms/farmers that are engaging in these practices in the southeast region.
An electronic fact sheet was written and is ready for publication pending minor edits to the University of Florida’s electronic fact sheet library (EDIS) titled: An Introduction to Biochar and Its Application to Soils (S. Friedman, D. Treadwell and A. Wilkie); HS 1205. Once finalized, it will be available at: A copy of this draft is included in the appendix.

Project Outcomes

Project outcomes:

Due to the high variability in the data and the inconclusive results, it was difficult to draw conclusions from the data. One constructive outcome of the project was the collaboration among various research groups evaluating methods of manufacturing and characterizing biochar for different end uses including carbon sequestion, bioremediation, and improved nutrient retention in soils. The extension fact sheet that was authored (described below) is expected to have a readership of 2,000-5,000 downloads a year.

Economic Analysis

Not addressed in this project.

Farmer Adoption

During the time the experiments were underway we conversed with many farmers about biochar. Primary concerns farmers had about using biochar were recommended rates of application, and how to identify a “good” material. Additional concerns regarding biochar included the cost of shipping the material from a commercial manufacturer to Florida, and the length of time expected before benefits would be realized following applications. While the answer to these questions were beyond the scope of this study, they did provide opportunities for constructive conversation regarding carbon sequestration, nutrient and water retention, and cost to benefit analysis of farm inputs.


Areas needing additional study

The use of biochar as an agricultural/horticultural amendment shows much promise but there is much work to be done. A more rigorous approach to field experimentation is necessary to demonstrate its short and long term effects to the soil and the farming system. Like compost, qualities of biochar are highly variable depending on the raw materials used and the method of manufacture. In this experiment, considerable time was spent discussing, evaluating and deciding the formulation of biochar to use for the trials. Future research should focus on evaluating and identifying the raw materials and methods of biochar manufacture for agricultural use, and focus future work on a limited number of standard formulations.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.