This year, 2024, Leon County leaders, becoming the first in the nation, voted to make permanent a test program to turn yard waste into a carbon-negative material called biochar.
Carbon negative means the product or process offsets more carbon, through carbon capture, sequestration, or avoidance, than it contributes to the environment.
Biochar is essentially charcoal, created from wood or other materials which have been partially burned at very high temperatures in anaerobic conditions to create a stable product which will sequester carbon for many years while rendering benefits to soil and plants.
Benefits of Biochar Additions in Soil
o Enhanced nutrient retention: Biochar has a porous structure that acts like a sponge, absorbing and holding onto essential nutrients like nitrogen, phosphorus, and potassium. This helps prevent nutrient leaching, ensuring that plants have a steady supply of nutrients for their growth and health.
o Improved water holding capacity: The porous nature of biochar also aids in retaining moisture in the soil. It can absorb water and release it slowly, reducing water runoff and evaporation. This means that plants have better access to water during dry periods, reducing the need for frequent irrigation.
o Increased microbial activity: Biochar provides a habitat for beneficial soil microorganisms such as bacteria and fungi. These microorganisms play a crucial role in breaking down organic matter and converting nutrients into forms that plants can readily absorb. By promoting microbial activity, biochar supports a healthy soil ecosystem and enhances overall soil fertility.
o Carbon sequestration: Biochar is a form of stable carbon that remains in the soil for an extended period, sometimes even for hundreds or thousands of years. By adding biochar to the soil, carbon from plant material is effectively locked away, mitigating the release of greenhouse gases into the atmosphere, and contributing to climate change mitigation efforts.
o Reduced soil erosion: The incorporation of biochar into soil can enhance its structural stability, preventing erosion caused by wind and water. It helps bind soil particles together, reducing the risk of soil loss during heavy rainfall or strong winds.
o Balancing pH and soil remediation: Biochar has the ability to adjust soil pH levels by acting as a buffer. It can help neutralize acidic or alkaline soils, creating a more suitable environment for plant growth. Additionally, biochar can aid in the remediation of contaminated soils by adsorbing pollutants and preventing them from entering the food chain.
o Long-lasting soil amendment: Biochar has a slow decomposition rate, allowing its benefits to persist in the soil over an extended period. This reduces the need for frequent reapplication and provides a long-term solution for soil improvement.
Biochar in Sandy vs. Clayey Soils
o When biochar is added to clay, it makes the soil less dense, and it increases hydraulic conductivity (the higher the hydraulic conductivity, the more easily water can move through soil).
o Adding biochar to sand also makes it less dense, but researchers have found that biochar-amended sand holds water longer.
o Sandy soils can be more responsive to biochar than clayey soils because of the larger differences in particle size between biochar and sand particles.
o Biochar application rates as low as 0.5% appeared to reduce saturated flow in sandy soils, but only >1% application rates appeared to increase saturated hydraulic conductivity in soils with high clay content.
o Application: To improve aeration in clayey soils, biochar can be tilled into the soil benefitting the entire root zone. For most other soils, including sandy soils, biochar can be top-dressed and blended into the upper layer of soil.
Biochar in the VegHeadz Garden.
Most sources agree that the addition of untreated biochar to the soil may temporarily immobilize nutrients, potentially leading to a short-term reduction in plant growth. Avoiding this result would require several months up to a year of fallow time after application of untreated biochar to allow the soil and its organisms to stabilize before planting.
After poring through a lot of online information about biochar, it seems that all the discussion about how it is made and what it is made of isn’t as important to a gardener as how it is treated prior to applying to the soil. The purpose of treating the biochar, called activating, or inoculating, or charging, is to fill the nutrient storage capacity of the biochar and pre-load it with microorganisms so it will cause the least disruption in the growing medium, and will immediately begin doing its work in the soil and providing nutrients to plants.
There are a number of approaches for the home gardener to charge or activate biochar.
Charging with Compost—This seems to be the easiest method if you have compost available, although it takes longer. It involves adding biochar in any amount up to a 1:1 ratio to existing compost and allowing it to “marinate” for four to six weeks. Some sources recommend soaking the biochar in water before mixing it with the compost to help nutrients move through the material easier. It’s also important to keep the compost/biochar mix quite wet during the charging period. This should allow time for microorganisms and nutrients to inhabit the many pores in the biochar particles, and for these processes to become stable. This can be scheduled so that it is ready when it is time to apply compost before planting, reducing or eliminating any fallow time.
The same thing can be accomplished over a longer period by adding biochar to your nitrogen and carbon materials when you are feeding your compost bin. In this way, the nutrients and microorganisms that are created in the composting process will inhabit the biochar at the same time.
According to the University of Arizona Extension, “Biochar lacks nutrients like nitrogen and phosphorous so mixing it with compost or manure is a helpful option. Biochar has the ability to absorb these nutrients and keep them in the soil longer and is better than using compost alone. Mixing up to 1 part compost with 1 part biochar is effective at increasing the time nutrients stay in the soil, but most gardeners start with ratios closer to 10 parts of compost to 1 part biochar to be sure that plants tolerate it well. Before adding this mixture to soils, or using it in a potting mix, it should be aged for several weeks under moist conditions to allow for the exchange of nutrients between the two materials. This will also help microorganisms, worms, etc., found in compost to adjust to the biochar. This step also helps beneficial fungi that grow on plant roots to develop quickly once the biochar-compost mix is applied to soil.”
Charging with liquid—This is a method which produces quicker results and biochar that can be applied sooner than the compost charging method. This method follows a common pattern—add nutrients, add liquid, and let it sit. Some proponents of this method claim that aeration of the liquid mixture is essential for the flourishing of microorganisms in the biochar since the beneficial organisms we want need oxygen to proliferate. This makes it similar to the method for creating bio-brew from compost or animal manure with biochar added to the mix. Look for Compost Tea or Bio Brew under Garden Resources in the left sidebar of the VegHeadz Blog for details on this method. A drawback is the inability to do this in larger amounts without multiple batches, and it requires an aeration device such as an aquarium pump.
If aeration is not used, the biochar can be activated by mixing in some source of nutrients, and letting it sit for approximately three days before adding it to your soil. The liquid is usually water, and the source of nutrients can be organic or conventional fertilizer, compost, manure, fish emulsion, worm castings, etc.
The llquid method will also furnish microorganisms to a greater or lesser degree, depending on the nutrient-supplying material used, but the short soaking period may not allow the microorganisms to develop to the same extent as the compost method, and access to oxygen is necessary for microorganisms to proliferate. Also, using this method to activate biochar in any substantial volume would be cumbersome for a home garden.
Biochar for Raised Bed Vegetable Gardens
The rate of biochar application in vegetable gardens can vary depending on the type of soil, organic matter content of the soil, and the plants being grown. A general rule of thumb is to apply 5 to 10% biochar by volume to the soil. For example, a typical 8 ft. by 4 ft. by 10 in. raised bed holds about 30 cubic feet of soil. Therefore, you could add 1.5 to 3 cubic feet of biochar per raised bed.
Biochar Trial in the VegHeadz Garden
Our goal at the VegHeadz garden is to run our own trial by planting some of the same plants in soil that does not include biochar, in soil with biochar added without charging, in soil amended with biochar charged with compost, and in soil amended with biochar charged with organic liquid fertilizer. Any differences in pests and diseases, and plant health and growth, will be noted.
Several gardeners have also taken small amounts home to try in their own gardens. One Master Gardener (MG) has a green house and tropical plants to protect. He soaked the biochar overnight with commercial liquid fertilizer, combined it with his potting mix, and applied it to his greenhouse plants. He reports that so far they look healthy with no adverse effects. He also added biochar to his compost bin to charge there and will use it on his spring garden.
We have several concerns or questions.
According to some sources, biochar tends to increase soil pH, and our soil test results reflect we are already operating at the high end of the desirable pH range. Other sources indicate that while biochar can indeed raise pH if it is extremely low, such as 5.0 or below, if the pH is close to neutral or alkaline it does not further raise the pH. This would tend to support the claim by some sources that biochar regulates pH. We had our soils tested this fall so we have a benchmark with which to compare biochar amended soils. This is highly recommended when adding amendments to your soil..
Second, in general, biochar seems to be more beneficial for sandy or poor, nutrient-depleted or acidic soils than healthy ones. Our soils are already healthy, and definitely not acidic, so our main purpose in using biochar would be to utilize its water and nutrient retention and microbe boosting capabilities, and its ability to sequester carbon and some soil-borne pathogens over long periods of time—to do our bit for the environment.
A third consideration is whether biochar can help remediate the copper concentration in our garden soil. Biochar is reported to be effective in sequestering copper contamination in soil. Our recent soil test indicated that our soil contains much more copper than recommended. It has been determined that it is probably from the use of animal manures in the garden mixes that we have applied, which is further concentrated by composting plant material from our garden that has been grown in the high copper soil. Copper is included in the feed for most domestic animals because of its antimicrobial qualities as well as for nutrition. The buildup of this element in our soil has affected seed germination and plant growth to some extent and will get worse if copper levels continue to rise.
Finally, it is important to proceed carefully when adding any amendment to your soil, and particularly biochar because once it’s there, it cannot be removed and it will not degrade naturally in our lifetime.
Some References:
USDA site: https://www.climatehubs.usda.gov/hubs/northwest/topic/biochar, lots of info and a wider view of potential uses and benefits of biochar
https://edis.ifas.ufl.edu/publication/SS585, UF/IFAS introduction to biochar and its uses in agriculture
https://www.rhs.org.uk/soil-composts-mulches/biochar. Biochar over view and use in gardens from the Royal Horticultural Society of Great Britain (RHS).
https://climate.mit.edu/explainers/biochar. A good explanation of how biochar works to sequester carbon dioxide over centuries.
https://www.southlandorganics.com/pages/faqs/the-power-of-biochar-how-long-does-it-take-to-charge-in-compost#:~:text=Optimal%20Charging%20Period%3A%20For%20optimal,of%20nutrients%20and%20beneficial%20microbes. Details about compost charging of biochar.
https://www.geoengineeringmonitor.org/growing-concerns-about-biochar-safety-and-carbon-markets#:~:text=A%20review%20of%20259%20studies,water%20availability%20and%20soil%20erosio. A more negative or cautionary view of biochar.
https://www.permaculture.co.uk/articles/how-to-charge-biochar/#:~:text=The%20simplest%20and%20most%20efficient,by%20maturing%20in%20your%20compost., A permaculture view of biochar charging and application.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10821463/ A more complete analysis by the National Institutes of Health
https://ohioline.osu.edu/factsheet/anr-36. role of soil bacteria and aerobic vs. anaerobic bacteria.
https://www.sciencedirect.com/science/article/abs/pii/S004896971732942X The ability of certain biochar to sequester copper contamination in soil.
Several sources with information about liquid activation of biochar.
https://bottom-up-biochar.com/7-ways-to-charge-biochar/
https://biochar6.com/activating-biochar/
https://soilfixer.co.uk/Biochar-activation-inoculation
Biochar Educational Materials
These organizations have ongoing research into biochar and/or good summaries/bibliographies of some of the more popular research that has already been conducted. The first two are the trade associations for the biochar industry.
- International Biochar Initiative
- U.S. Biochar Initiative
- Yao Lab at Yale University School of the Environment
- Bioeconomy Institute at Iowa State University
BIOCHAR OVERVIEW STUDIES/ARTICLES
- Properties of Biochar
- How Biochar Works and When it Doesn’t
- Combined Effects of Biochar Properties and Soil Conditions on Plant Growth
- Biochar application to soils
PUBLIC/END USER ARTICLES
- Biochar: A home gardener’s primer, Washington State University Extension
- Biochar: An emerging soil amendment, Michigan State University Extension
- Guide to Making and Using Biochar, University of Arizona Extension
- How to Use Biochar, Wakefield
In addition to the above, the International Biochar Initiative undertook a fairly significant campaign in 2018 focused on research and public education as part of their Biochar For Sustainable Soils (B4SS) Campaign. There are some good resources that run the spectrum from full scientific articles to cartoons on their campaign site.
No comments:
Post a Comment