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Beyond the biochar hype—how to decide if it’s right for you
Four key takeaways about using biochar in agriculture
September 4, 2024
Author: Dani Gelardi
In 2021 I finished my dissertation about the agronomic (yield, crop quality, soil fertility, cost), soil health (carbon, soil microbes), and societal (externalities, greenhouse gas emissions) impacts of using biochar as an agricultural soil amendment. Like many researchers during grad school, I was burnt out on my topic and never expected to write about biochar again. However, the people keep asking for more! To wrap up the WaSHI blog series on biochar, and to help you decide if biochar is right for you, I’ll summarize some big-picture takeaways from our previous articles and from my own research at UC Davis.
Takeaway #1: It's complicated
While the hype may have you believe that biochar is a universal cure-all, I hope our series has shown that there is much more nuance and complexity to the story. As Dr. Kristin Trippe perfectly described: The way a soil or a crop will respond to biochar application depends on what the biochar was made from (feedstock) and how the biochar was made (production conditions). Add in variables from the soil, cropping system, and climate, and you have yourself quite the experimental tangle!
Fortunately, as Kristin described, there are several new resources to help you select the right biochar for the right conditions to increase your chance of success (explore the resources and/or listen to Casey Vetch detail her decision-making process about what biochar to use and at what rate in Washington orchards). But before you use these tools or make your decisions, there’s an important question to ask: What does success even mean for your farm?
Takeaway #2 : You'll have the most success when you pre-define success
While the biochar in Dr. Si Gao’s study provided multiple benefits in San Juan County, it’s important to remember that won’t happen for everyone in every condition. Biochar can provide many agricultural benefits (Figure 1), such as increased yields 1–4, soil fertility 5,6, or soil water retention 7,8. However, these benefits are not consistent across soil textures 9–12, and biochar types 13,14, and can be minor, short-lived, or nonexistent 15–20.
Read about biochar on the San Juan Islands
The most consistent agricultural benefits have been observed in suboptimal agricultural soils 12,21,22, such as saline or sodic 23–25, contaminated 26,27, highly acidic 28, or low fertility soils 12. In fertile soils, temperate climates, and cropping systems with regular inputs of irrigation and fertilizer, biochar may deliver fewer agronomic improvements 19,23,28–31.
FIGURE 1 | Potential benefits of biochar production and use, which are not universal across all biochar, soil, and crop contexts.
From Gelardi and Parikh (2021) doi.org/10.3390/su131810079 32
So, is your soil acidic? Then, as Dr. Claire Phillips and Dr. Kristin Trippe described, you may find great success in using a high pH biochar to neutralize the soil. But if you farm in the Umapine soil series (pH > 9!) near Kennewick, adding the same biochar would make your problem worse!
Do you have a fertilizer problem? In my own research, I tested seven biochars for their ability to retain nitrogen33–36. Because most biochar surfaces have a negative charge, they are great at attracting and retaining the positively charged ammonium ion (NH4+). In the cropping system I studied, however, nitrate (NO3-) is the primary nitrogen source. And because it’s negatively charged, biochar does little to retain it.
So, are you fertilizing with ammonium? Perhaps biochar could improve your fertilizer use efficiency. But with nitrate? You may find less success.
If you have a clearly defined soil problem, there’s a good chance that the resources Kristin described could point you toward a solution. But perhaps you’re less interested in agronomic success, and instead motivated by mitigating climate change? Read on.
Takeaway #3: Biochar production sequesters carbon, even when the biochar is not added to soil
An engineering professor once joked to me that, despite society’s technological advancements, our only bright idea for waste products is to “add them to concrete or put them in the soil.” While we might add biochar to soils for many positive and beneficial reasons, her joke emphasized that alternative options may also be worth exploring.
The global policy push to produce biochar stems largely from an interest in mitigating climate change37,38, as biochar production converts carbon from waste products (i.e., tree prunings, corn stover, almond shell) into more stable forms.39 Once the biochar is made, that carbon isn’t going anywhere for hundreds—maybe thousands—of years. Even if the biochar isn’t added to soils. Even if the biochar is landfilled! However, the economic feasibility of large-scale biochar production (and the desire to optimize potential co-benefits) requires viable secondary markets for the material38,40,41. This may bolster the addition of biochar to agricultural systems, even in soils that do not require conditioning.
There are many alternatives to agriculture for biochar use, some of which may deliver greater societal benefits and at less cost 32. For example, biochar can be incredibly effective at removing contaminants from soils and water42–44, or at treating wastewater or stormwater45–48. My personal favorite is its role in replacing non-renewable, mining-intensive materials, such as peat in potting mix49–53, or odor control clays in cat litter or animal bedding54,55. For agriculture, biochar may play a huge role in reducing greenhouse gas emissions from composting operations, which has the dual benefits of “pre-loading” biochar with nutrients56,57. The below decision tree (Figure 2) was developed to help policymakers, biochar producers, and farmers decide if biochar should indeed be added to soils, or if another option may provide greater benefits.
FIGURE 2 | Decision trees for the sustainable production (left) and use (right) of biochar, to aid in optimizing environmental and economic benefits.
From Gelardi and Parikh (2021) doi.org/10.3390/su131810079 32
Takeaway #4: Advanced planning can optimize benefits and minimize costs or unintended consequences
Of course, there are other soil health benefits that biochar may provide. In my California field trials, not one of the seven biochars improved yield, soil moisture, or fertilizer use efficiency after three years36. However, in our slightly less fertile and more coarse soil, we saw a shift in the microbial community that indicated less environmental stress 34. We also saw an increase in permanganate oxidizable carbon, which may indicate a future increase in soil organic matter.
Though biochar is often described as a profitable climate change mitigation strategy due to its potential to increase yield and farmer income, my results, and many other economic analyses, suggest otherwise 58,59 due to high biochar pricing 60,61, widely variable biochar pricing 59 or the inconsistent delivery of benefits 61,62. This brings up an important question about who should pay for the biochar.
In Si’s study, perhaps the yield increase would be enough to entice a farmer to pay the price per acre to buy and apply biochar. In my study, however, a farmer may be frustrated to see no agronomic improvements after three years.
If you are using biochar to solve a specific issue, it’s possible the cost would be worth it. But if you’re more interested in global soil health improvements, or in “doing your part,” consider taking advantage of new incentives63 or subsidies to offset the private costs of providing those public benefits.
Regardless of what biochar you choose, for what purpose, and who pays for it, care should be taken to minimize potential consequences64.
While making biochar, there are many strategies to reduce air pollution or the development of toxins in the biochar like heavy metals, dioxins, or polycyclic aromatic hydrocarbons (PAHs): never use feedstocks from construction and demolition, which may contain treated woods or other chemicals; make sure your feedstock is dry, as moisture leads to incomplete combustion and PAH formation; consider rinsing or aging the final product before application, to remove excess soluble salts and chemicals.
When applying biochar, it’s essential to minimize the potential that you, farmworkers, or neighboring farm communities will inhale the material: wet the biochar before applying; do not apply on a windy day; wear the appropriate protective equipment. See the images below for details of the dos and don’ts of biochar application.
RECOMMENDED
Here, biochar is applied to the field at 40% moisture content (a), using a subsurface banding technique (b) in which biochar is immediately covered by soil (c) so it is less likely to pollute air or water during wind- or rain-driven erosion. The worker is protected with a respirator, gloves, and goggles.
NOT RECOMMENDED
Here, biochar is applied at 0% moisture content (d), on a windy day (e), and left on the soil surface where it became airborne (f). The worker (Me! Before I knew any better ☹) is unprotected, and has biochar on her eyes, nose, and mouth.
DOS AND DON'TS OF BIOCHAR APPLICATION | Practices that are recommended (top) and not recommended (bottom) for the application of biochar.
Adapted from Gelardi et al. (2019) doi.org/10.1016/j.scitotenv.2019.05.007 64and Gelardi and Parikh (2021) doi.org/10.3390/su131810079 32
Read more about biochar
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Dani is the Senior Soil Scientist and Climate Coordinator at the Washington Department of Agriculture where she leads soil and climate efforts for the agency including the Washington Soil Health Initiative.
This article was published by the Washington Soil Health Initiative. For more information, visit wasoilhealth.org. To have these posts delivered straight to your inbox, subscribe to the WaSHI newsletter. To find a soil science technical service provider, visit the Washington State University Extension website or the Washington State Conservation District website.