Inspection Services Blog

Research Update: Evaluation of Biochar

Note: This is part of a Research Update series that highlights projects funded by the Fertilizer Research and Education Program (FREP) annual grant program.

Project Title: Evaluation of Biochar for On-Farm Soil Management in California

Project Leaders: Danielle Gelardi, Sanjai J. Parikh, William R. Horwath, Daniel Geissler, Toby O’Geen, Kate M. Scow (UC Davis), Milt McGiffen (UC Riverside), Michelle Leinfelder-Miles (UC ANR)

Project Status: Year 2 of 3

Overview: This FREP-funded project will provide baseline data for biochar application to agricultural lands in California’s Central Valley. More specifically, this project is evaluating biochar’s potential as a soil amendment for impacting crop yield, soil moisture, nutrient retention and carbon sequestration, with attention paid to agronomic parameters such as biochar application rate and fertilizer rate.

Background: Biochar is produced from pyrolysis, a high-temperature decomposition of biomass (agricultural and forestry waste), and it has been proposed as an effective way to increase soil carbon stocks and improve soil health and ecosystem services. However, due to differences in biochar feedstock, production methods, soil properties, climate and cropping systems, there have been inconsistent reports on biochar impacts in agricultural systems. Results vary as to biochar’s ability to increase crop yields while addressing issues such as nitrate leaching, nutrient-use efficiency and soil organic matter levels. Thus, there is a need for reliable and localized research data to inform growers, stakeholders and policy makers of the benefits and trade-offs of biochar use on agricultural lands. The project aims to fill this knowledge gap by providing long-term empirical research data about the potential of biochar to boost crop yields and nutrient-use efficiency while minimizing nitrogen losses in the field.

Approach: The researchers tested basic physical and chemical properties of seven types of biochar, produced from different feedstocks and temperatures. Table 1 shows different types of biochar used in this study, the method of pyrolysis, and important physical and chemical properties.

Table 1. Biochar characterization data. All values reported as mean (n=3). Abbreviations: EC, electrical conductivity; CEC, cation exchange capacity; DOC, dissolved organic carbon.

IDFeedstockPyrolysisCarbon (%)Nitrogen (%)Oxygen (%)Ash (%)pHEC (ms cm-1)Surface area (m2g1)CEC (cmolc/kg)DOC (mg/kg)
NO (Control)
ASalmond shell (raw)
CS650coconut shellslow71.20.813.
SW500-Isoftwood sawdust w/ inoculanthydro63.50.720.
AS50075% almond shell, 25% softwood sawdusthydro65.80.817.
AS800almond shellgasification35.30.626.455.410.127.2188.252.7479.3
SW500softwood sawdusthydro70.90.117.1 4.5 7.82.593.516.543776.2
SW800softwood forestry thinningmixed41.8 0.1 15.331.510.32.7363.660.8631.4

In 2017, the researchers carried out a growth chamber experiment to test the effects of seven types of biochar, a raw almond shell amendment, and the control (no biochar) (Table 1) on romaine lettuce biomass and nitrogen accumulation. In addition, they established two three-year field trials in Davis and Parlier, Calif. Researchers subsurface banded each biochar at four rates (high, low, tiny, and control), in combination with low (150 lbs N per acre) and high (225 lbs N per acre) UAN-32 fertilizer rates. The experimental design is a randomized complete block design with three replicates per treatment combination. Processing tomatoes were planted each spring and harvested each fall, with data collected on marketable tomato yield, as well as plant and soil carbon and nitrogen content. The researchers developed a nitrogen budget to calculate and determine nitrogen losses through leaching and volatilization loss pathways. The data collection and analysis are ongoing in the lab and field experiments, with the third and final field season beginning in spring of 2020.

Preliminary results: Although not statistically analyzed, the researchers indicated that biochar produced from pyrolysis of pine (SW650) and coconut shell (CS650) had the highest concentration of carbon, respectively. However, the highest concentration of dissolved organic carbon (DOC) was observed in the softwood sawdust biochar (SW500) (Table 1). The results of growth chamber experiment showed that AS800 was problematic for plant growth; however, all other biochars showed no negative effect on plant growth parameters. Preliminary data suggest that CS650, SW650-M, SW500-I, and SW800 provide the most benefit for plant growth (Figure 1, left). Also, AS and AS500 indicated slightly smaller biomass accumulation compared to the control (Figure 1, left). SW500-I, SW500, and CS650 biochars resulted in higher plant tissue nitrogen concentrations compared to the other biochar types and control (Figure 1, right).

Two bar charts.
Figure 1. Plant biomass accumulation (left) and total plant nitrogen concentration (right) for lettuce for each of the biochar treatments and a 0% biochar control (NO). All values reported as mean + SE for experimental replicates (n=4)-2017.

In the Davis trial, tomato marketable yield (Figure 2) and nitrogen losses through volatilization and leaching (Figure 3) varied depending on the nitrogen and biochar application rates. Results from the Parlier site are pending.

Figure 2. Marketable yield from season 1 (2018) processing tomatoes from Davis trial. High fertilizer rates (225 lbs-N/acre) at left (a) and low fertilizer (150 lbs-N/acre) at right (b).
Figure 3. Nitrogen losses through volatilization and leaching in Davis at (a) high (225 lbs-N/acre) and (b) low (150 lbs-N/acre) UAN-32 fertilizer rates.

The impacts of different biochar sources and application rates and their interaction with nitrogen application rates are yet to be determined. At the close of this project, there will be a more comprehensive understanding of biochar’s effects on tomato yields, soil carbon sequestration and nutrient retention for Central Valley, Calif.

CDFA FREP funds projects on research and education regarding the agronomically safe and environmentally sound use of fertilizer in California. Visit for more information about the annual FREP Grant Program. Visit for details about current and completed FREP-funded projects, as well as a searchable database that aims to make the research available, understandable and convenient for growers to implement.

3 Responses to Research Update: Evaluation of Biochar

  1. Cathryn Guillette says:

    So what about the carbon pollution produced while you burn the materials? The CO2 emissions from pyrolysis?

    • Hi Cathryn, we’ve asked the researcher to provide information about CO2 emissions, and we will get back to you with more information. Thanks for the question!

    • Dani Gelardi says:

      Hi Cathryn,

      Thanks for the great question. Pyrolysis occurs in low oxygen conditions, so there isn’t the same quantity of CO2 produced as when something “burns” or combusts (organic material (C) + O2 = CO2). Instead, by limiting the quantity of O2, much of the organic carbon is converted and stored in the biochar, bio-oil, and/or syngas. That being said, there can still be CO2 (and other volatile emissions) released from pyrolysis. The quantity depends on the the type of process itself (and other parameters such as how long the feedstock is pyrolized, the moisture content of the feedstock, the type of feedstock, the max temperature, etc). For example, low-tech open kilns are likely to produce more volatile emissions (including particulate matter (PM) which has consequences for air quality) than really advanced gasifiers which have built-in mechanisms to capture any gases .

      The information above is specific to CO2 released during the actual production process. Of course there can be CO2 release (and other negative impacts) from elsewhere in the biochar life cycle. For example, how far the feedstock is shipped to the pyrolysis facility really matters in terms of oil and gas use, or whether or not the feedstock is a waste material, or a crop grown specifically for biochar/syngas production. If you search for “biochar life cycle assessment,” you can find some really interesting papers on this topic!

      I hope this answers your question!

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