Improving nutrient retention with biochar

Project Overview

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

Annual Reports


  • Vegetables: greens (lettuces)


  • Crop Production: municipal wastes, nutrient cycling, organic fertilizers
  • Education and Training: extension
  • Energy: bioenergy and biofuels
  • Natural Resources/Environment: carbon sequestration
  • Production Systems: organic agriculture
  • Soil Management: earthworms, nutrient mineralization, organic matter, soil analysis, soil quality/health


    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.

    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.