Soil Amendment and Carbon Sequestration with Biochar

We are all experiencing climate change whether its extreme weather events, water scarcity, or wildfires [1] like Jasper in 2024 (Figure 1+2). I have seen the impact of climate change on plants. In my garden the past few years saskatoon berries and raspberries have shriveled before being harvested due to the drought-like conditions brought on by climate change.

My project, using biochar, tackles one greenhouse gas, carbon dioxide while also improving soil for agriculture. I hypothesized that if biochar is added to soil then it will grow a taller plant because it retains more water and nutrients. (Figure 3)

Biochar is a carbon rich material produced by heating biomass without oxygen, this is done in a pyrolysis kiln. When biomass is heated without oxygen the carbon is stored inside the biochar instead of being emitted. [2] (Figure 4) Another example of pyrolysis is turning carbon fiber polymers back into carbon fiber. [3]

My project tested biochar's ability to retain water and nutrients using a small-scale replicable test that farmers of any scale without lab access can perform on their own. I also tested the practical benefit of biochar in agriculture by growing oat grass seeds with and without biochar. Biochar is currently minimally used in agriculture as it is not well known and produced.

This project supports the potential to benefit gardeners and farmers. When farmers use biochar they are augmenting their crops. (Figure 5) Companies producing biochar sequester carbon, which is a preventative measure against climate change. [4]

Background

Pyrolysis is the process through which biochar is made. It has 5 stages (Figure 6), the main one being the pyrolysis reactor or kiln where dry, ground biomass is heated to between 300-700° Celsius without oxygen. No carbon dioxide is produced as there is no oxygen for the carbon to bond with. [5] In this stage the biomass, before becoming biochar, cracks apart and comes together. This action creates the microscopic pores that provide biochar with a high surface area(Figure 7). High surface area allows biochar to absorb water, adsorb nutrients and host microbial growth.

Experiments

Water Retention: I performed this test by soaking biochar in a jar with water for 24 hours. After 24 hours, I filtered the water from the biochar and measured the amount of water that filtered out. I subtracted this from the amount I poured in to calculate the amount of water retained. I repeated this experiment using soil as a comparison. (Figure 8)

Nutrient Retention: I performed this test by saturating biochar with fertilizer for 24 hours before filtering the fertilizer out and measuring the resistance of the biochar. I converted the reading of resistance into conductance by calculating the inverse of resistance. Conductance relates to nutrient retention as it is an indicator of the amount of ions that the biochar can hold. Higher conductance indicates higher nutrient retention. I repeated this experiment using soil as a comparison. (Figure 9)

Plant Growth: I performed this test by mixing the growth medium (soil or biochar), fertilizer, and soil together. Let the mixture sit for 24 hours. The next day I added the mixture to plant pots and planted 3 seeds in each pot. I watered the seeds every two days and took a height reading every day over the next 10 days. (Figure 10)

Results

Water Retention:

Figure 13 presents my water retention results in a clustered column chart, showing each trial as well as the average of the two trials.

The following findings supported my hypotheses.

Biochar retained more water than soil alone

Biochar made of pine, spruce, and cedar (varied feedstocks) retained more water than biochar made of just pine for the same granularity

The following findings refuted my hypotheses.

Medium biochar retained the most water followed by fine. This may be because the fine biochar was too small and the pore structures had collapsed which reduces the sponge like ability of biochar to absorb water.

Nutrient retention:

Figure 14 presents my nutrient retention results in a column chart, showing the average of the two trials I performed.

The following findings supported my hypotheses

Biochar retained more nutrients than soil alone

Biochar made of varied feedstocks retained more nutrients than pine alone regardless of the granularity

The following findings refuted my hypotheses.

Medium granularity of biochar retained the most nutrients followed by fine. This may be because the fine biochar was too small and the pore structure had collapsed reducing the surface area and the amount of nutrients it can retain.

Plant Growth:

Figure 15 presents my plant growth in a box plot showing results from all three of my trials.

All my plant growth hypotheses were supported

Biochar grew a taller plant than soil alone

Medium granularity of biochar supported the growth of oat grass the most, followed by fine biochar

Biochar made from varied feedstocks performed better than biochar made of just pine

All biochars greatly improve soil’s ability to grow and increase the size of plants.

Overall

My results show that biochar can play an important role through not only it's already proved carbon sequestration, but soil amendment as well by improving at least two specific characteristics of soil, water and nutrient retention. Additionally, my water retention and nutrient retention testing framework is a simple and accurate way for farmers to test the biochars they buy for the properties they would like to amend based on the needs of their soil. For instance if farmers have a silty soil they may want to amend the low nutrient retention over the water retention.

Biochar is a beneficial material that not only keeps carbon out of the atmosphere, [6] but can also be used as a scalable soil amendment by anyone from hobby gardeners to commercial farmers.

Agriculture

My results show that most biochar have a higher water retention level compared to soil as well as a higher nutrient retention. (Figure 16) The ability of biochar to improve these two qualities of soil is incredibly useful, especially as these properties can be tailored to the needs of the soil based on the feedstocks and granularity of the biomass being put into the pyrolysis kiln.

My two tests can be used as a framework by farmers who want to understand what qualities their soil lacks and which qualities they would like amended. Additionally, my tested framework can be applied by farmers of any scale and most means, as it is low-cost and the materials are readily available to most farmers.

Climate Change

Biochar not only sequesters carbon, it also prevents biomass from being burned which is a common disposal method that releases carbon dioxide into the atmosphere. [7] Biochar is a better alternative to charcoal in soil because it is more porous which is better for the soil. As charcoal is designed for burning it is also made to have a high carbon content, but not with long-term sequestration in mind as it  is expected to be burned. Because of this, charcoal decomposes much quicker and often has chemicals harmful to plants in it. [8]

I would like to continue my research into the production of biochar through pyrolysis. Additionally, I would research the usage of excess heat from oil and gas producers or other industrials to heat pyrolysis kilns. This would not only benefit the industrial producer by earning carbon credits, it will likely also increase the accessibility and lower the cost of biochar. (Figure 18)

I would also like to research into the production of small scale pyrolysis kilns that are being used in impoverished countries to provide an alternative to burning waste and produce an agricultural amendment. (Figure 19)

I would like to thank Professor David Layzell who put me in contact with Rob Lavoie and Don Harfield. These two people greatly helped my project by providing me with resources and insight about biochar.

I would also like to thank Mme. Girard for approving my project and for coordinating the science fair at my school.

Next, Thank you to Mme. Aragon who provided me with a multimeter and seeds to perform my experiment.

Additionally, thanks to Agriculture Canada who I reached out to and obtained and used informative resources from.

Thank you to my parents who helped me get through this project and for supporting me.

Lastly, thank you to the CYSF delegates who provided helpful resources to me and all of team Calgary.

ProjectBoard Citations

1.  Environment and Climate Change Canada. (2019, Spring). Canada’s climate is warming twice as fast as global average. Retrieved from https://www.canada.ca/en/environment-climate-change/news/2019/04/canadas-climate-is-warming-twice-as-fast-as-global-average.html

2.  Lehman, J., & Joseph, S. (2009). Biochar for Environmental Management. Earthscan.

Property and Environment Research Center.

3. The American Society of Mechanical Engineers. (2021, Summer).Unlocking Composite Carbon Fibers for Recycling. Retrieved from https://www.asme.org/topics-resources/content/unlocking-composite-carbon-fibers-for-recycling

4.  Lehman, J., & Joseph, S. (2009). Biochar for Environmental Management. Earthscan.

5. Yaashikaa, P.R., Kumar, P.S., Varjani, S., & Saravanan, A. (2020). A critical review on the biochar production techniques, characterization, stability and applications for circular bioeconomy. Biotechnology Reports, 28, 3-5.

6.  Lehman, J., & Joseph, S. (2009). Biochar for Environmental Management. Earthscan.

7.  International Biochar Initiative. (2018, Winter).Removing Carbon. Retrieved from https://biochar-international.org/about-biochar/sustainability-climate-change/#:~:text=Biochar%20can%20improve%20soil%20health,the%20Voluntary%20Carbon%20Credit%20Market

8. Carbon Gold. (2007, Winter). Is Biochar just Charcoal?. Retrieved from https://www.carbongold.com/is-biochar-just-charcoal/

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