Biochar

#207Biochar

also available for: Honduras, Guatemala

Applicable for:
Arabica, Robusta

207⸱AConcept

  • Improves soil structure and organic matter 
  • Improves plant nutrition 
  • Increases the coffee yield

Biochar is used to improve soil fertility. It can be produced from any carbon-based feedstock, e. g. crop residues such as coffee husks, wood, rice hulls, etc.

The plant-based feedstock is converted into biochar by heating it up to ca. 500°C with little or no oxygen. This process is called pyrolysis. During this process, the contained cellulose, lignin, and other materials are transformed into gases, liquid (bio-oil), and a solid material called biochar. Biochar consists of carbon and mineral nutrients. The carbon in biochar is much more stable than in the original biomass and does not decompose easily.

Applied to the soil, biochar serves as a soil conditioner. It rapidly improves soil quality and fertility, especially in soils that have a low water retention capacity, such as sandy soils. Why is that so? Biochar is a porous material that can retain water and air. The biochar surface features a high cationic exchange capacity that is able to store plant nutrients such as NH₄⁺, K⁺, Ca²⁺, etc., and to gradually release them to the soil and plants. Areas with low rainfall or nutrient-poor soils will therefore most likely benefit the most from the addition of biochar.

207⸱BTo be considered

There are different ways to produce biochar from artisanal to high technology pyrolysis machines:

In a pit in the ground: This is the most basic way to produce biochar. Wood and other heavier plant-based feedstock can be applied. Light materials such as coffee husks or rice hulls should not be used as they would burn to ashes very quickly and uncontrolled here.

In a kon-tiki: This is a cone-shaped container made of metal that facilitates the handling. Here also, wood and other heavier plant-based feedstock can be applied.

In a pyrolyzer: This is an “oven”, that permits a more controlled process and the use of lighter and less dense materials such as coffee husks or rice hulls.

Biochar improves soil quality and fertility but usually it does not contain enough and balanced nutrients by itself. Therefore, it is recommended mixing it with fertilizers such as Bokashi. A mixture ratio is recommended in the application recipe below. Generally, it is recommended to perform a soil analysis before applying any fertilizers. This provides information about the amounts of nutrients needed.

Biochar can also be used to improve the process of producing compost as a soil fertilizer. See Compost.

Timing: The production takes around 2 days, depending on the amount and number of pyrolysis repetitions and the used technique.

The use of biochar as a soil conditioner requires some patience. There might be an initial “neutral” year. However, a single biochar application has been observed to provide benefits for crop nutrition for several years afterwards. First improvements of soil quality will be seen in the second year after application. Usually, it further improves with biochar aging in the soil which leads to increasing crop yields over time.

207⸱CImplementation

Most common in Brazil is the basic way, using a pit in the ground and coffee wood for the pyrolysis process. However, we invite you to review other forms of pyrolysis used, for example, in Central America.

Materials

For 1 ha

207⸱1Preparation

Collecting wood

a group of people are standing on a dirt path in a field .
a group of people are standing on a dirt path in a field .
a large pile of wood is sitting in the back of an orange dumpster .
a pile of wood is sitting on the ground next to a black tarp .
a stack of sticks is sitting next to a scale that says ' king ' on it
a pile of wood is sitting on the ground next to a yellow bucket .
Digging a pit
a man is digging a hole in the dirt with a shovel .
a man is measuring a hole in the ground with a tape measure
a man is digging a hole in the dirt with a shovel
a man is digging a hole in the dirt with a shovel
a man in a hat is measuring a hole in the ground
a man wearing a hat is digging a hole with a shovel .
Attention

The flames might reach high and the heat is intense. That needs to be considered, when choosing the place.

Tip

Using wood of the same size is better for the production of biochar. They will burn more evenly.

207⸱2Production

To process the full amount of 10 tons, the pyrolysis described here will need to be repeated several times when using only one pit at a time. Each batch will take around 3-4 hours.

Carbonization of the wood

fire in a hole
Tip

The wood shall be added at a rate that allows the fire to consume the material. If you add it too slowly, the fire will start to die, and smoke will appear. If you add it too fast, it will burn too much of your residue, and you will end up with only little biochar and lots of ashes. The right speed is that of when the fire is stable, with orange flames and no smoke.

207⸱3

Stirring the fire

two men are standing around a fire in the dirt .
Tip

Make sure the pyrolysis temperature is high enough to burn off all oily deposits which may be phytotoxic. You see that the process and temperature is correct when there is no smoke.

207⸱4

Tip

Make sure, the wood does not burn to ashes!

207⸱5

Loading the ready biochar into a cart

a man is standing next to a wheelbarrow filled with ashes .
a man is standing next to a wheelbarrow filled with ashes .
a person is holding a pile of coal in their hands

207⸱6

The final biochar product should be a dark, porous, and odor-free material. After drying, it should have a water content of no less than 10 % so that it is not too dusty or powdery. Some humidity can be felt when squeezing it in the hand but without water coming actively out of it.

The final biochar

a group of men are standing around a large pile of coal .

207⸱7Application

Dosage:

For 1 hectare

  • 2,5 tons of biochar. Equals the outcome of the pyrolysis process of 10 tons of biomass as in the preparation recipe.
  • 7 tons of bokashi (depending on soil analysis)
Tip

Ideally, a soil analysis should be performed to evaluate the right amount of fertilizer.

207⸱8

207⸱9

If preparing a fresh coffee field for the plantation of new seedlings:

207⸱10

If applying to existing coffee plants in a field:

Storage

The biochar can be stored in a storage room in big bags, raffia sacks, or plastic boxes with a lid. As it is a very stable product, it doesn’t require high-maintenance storage.

It can be stored for 1 to 2 years before applying it.

207⸱DEconomic benefits

Lower fertilizer costs

This tool allows for a lower demand for synthetic fertilizers and therefore saves input costs over time.

Higher coffee yield

The effects of this tool can lead to a higher coffee yield and therefore a higher income.

Re-use of waste

The economic potential is particularly high if the waste products that serve as tool ingredients are produced on the farm or in the neighborhood, for example, manure from own cattle, straw or wood from the own field. Furthermore, by utilizing waste, this tool helps reduce landfill fees.

207⸱EGreen benefits

Less synthetic fertilizers needed

This tool reduces the need for syntheticfertilizers. This reduces carbon emissions and water pollution, improves soil life, and saves resources.

Re-use of waste

Reusing organic waste material in a circular economy saves resources from being discarded. This reduces the environmental load, carbon emissions, and water pollution.

Carbon storage

This tool removes CO₂ from the air and stores it. This helps to reduce CO₂ levels in the atmosphere.

207⸱FFurther readings

Links

About Biochar