October 1, 2018

By: Ron Kushner

What is it?

Biochar is a solid material obtained from the carbonization of biomass in an oxygen-limited environment. It is produced by the decomposition of organic material under a limited supply of oxygen at low temperatures. The process is similar to the production of charcoal.

Biochar differs from charcoal in that it is used as a soil amendment to improve soil functions and reduce emissions from biomass that would otherwise degrade to greenhouse gases. Charcoal briquettes are made from lower temperatures that cause tars and oils to remain, providing fuel for cooking but not a material for your soil. It is a smoldering process that is highly polluting. Biochar uses a higher temperature causing most of the tars and oils to burn out, leaving a pure carbon char, mostly carbon and minerals from ash.

There are many different kinds of biochar. It can be made from wood, grasses, bamboo, nut shells, corn cobs, fruit pits, rice hulls, manure and bone. All of these materials have different properties resulting in varying content of ash and minerals.

How is biochar supposed to help our environment?

The creation of biochar has been considered by some as a 2,000 year old practice converting agricultural waste into a soil enhancer than can hold carbon, boost food security, increase soil biodiversity and discourage deforestation. The process creates a fine-grained, highly porous charcoal that helps soils retain nutrients and water.

Biochar is found in soils around the world as a result of vegetation, fires and historic soil management practices. Biochar-rich earth in the Amazon has led the way to discovering its unique properties as a soil enhancer. It could be an important tool to increase food production and diversity in areas with depleted soil, lack of organic resources and inadequate water supply.

Supposedly, increasing the soil retention of nutrients and agrochemicals will result in the improvement of water quality. More nutrients will remain in the soil instead of leaching into groundwater causing pollution.

According to the International Biochar Initiative, “the carbon in biochar resists degradation and can hold carbon in soils for hundreds to thousands of years reducing carbon emissions”.

Biochar stimulates the activity of soil microorganisms that affect the microbiological properties of soil. Because it attracts and holds nutrients, it can reduce fertilizer requirements.

How can we actually use biochar in the soil?

In many cases, it is necessary to charge the biochar with nutrients and microbes before use. This action would depend on the soil pH and the amount of biochar used. If a large quantity of biochar is to be added, it is best to add nutrients at the same time. The best way to charge biochar is to compost it with other organic material.

It is best to add biochar in small amounts every year and allow it to slowly build up in the soil. The amount could vary from as little as 1% and as much as 20%. Large amounts of biochar added to soil must be mulched, as the biochar can wick water to the surface where it evaporates and dries the soil surface. Also, testing the pH of the soil after application is a must as biochar could have a very high pH due to the content of wood ash.

Field trials
  • Virginia Tech – Their report on the effects of biochar on corn showed mixed results. Corn plants with biochar grew higher and fuller with an increase in productivity. With some other plants, productivity decreased. The mixed results could be due to the variety of biochars used or the variation in soil where it was applied. Different plants react differently  to the addition of biochar. Biochar appears to have increased the soil surface area retaining more nutrients and increasing the capacity to hold water.
  • The International Biochar Initiative – Many field studies have been performed for their research in a variety of locations, soil types and climates. Mixed results were achieved. Corn yields showed high increases in some control plots while others showed no difference and some a decline. Rice field studies showed little increase in yield. On the other hand, wheat production in Australia showed significant yield increases with the application of biochar. A study of soybean production in Quebec, Canada showed a 20% increase in biomass in the plots where biochar was added.
  •  Oak Hill Farm in Sonoma, California – In 2015, a green manure cover crop using biochar and compost was grown on a 1/4 acre test plot next to a plot of the same size where no biochar was used. After the cover crop was plowed in, winter squash was planted on both plots. The test plot with biochar grew larger plants with larger size and weight of fruit than the control plot but also had more weeds requiring greater labor. The test plot with biochar withstood high temperatures better as more moisture was retained in the soil. A concern was the purchase price of the biochar, a constraint against its further use.



It is my personal belief that organic practices and the creation of humus from the composting of all organic material created is still the solution to our agricultural problems. Not the creation of some new material created by burning stuff in factories. Cutting back on emissions we are spewing into the air is a fundamental requirement for environmental well-being in the future.

That being said, small amounts of biochar added to the soil can be productive, especially when composted first with other organic matter.

Biochar can improve the water and nutrient holding capacity of the soil but it is not a fertilizer.

A better understanding of the variables of how biochar is produced, the soil composition and the existing nutrients needs to be established before biochar can be recommended for positive results.

One of the main benefits touted in using biochar is its ability to remove carbon from the air and placing it back into the soil. If this assumption is true, it has not been proven scientifically.

Biochar is not humus. It is unclear how humus and charcoal interact. Thus, the different test results in different soil types and climates.

The biochar market is still in its infancy but there are sellers. A good place to start is your local garden center. Buy a bag of biochar and create your own evaluation on your crops. It could be done simply in two small raised beds or in containers. I would be very interested in hearing about your results.

For questions or comments: ron@primexgardencenter.com