Dome School Biochar Experiment Report

Date: May 12 2010


The purpose of this experiment is to find out if plants grow better in biochar. We tested 3 different kinds of biochar.


Our hypothesis is that biochar added to soil will help plants grow bigger and better than plants grown in soil without biochar.


1. First, we made 3 kinds of biochar. We bought lump wood BBQ charcoal in bags. We collected urine from our families. We got seaweed tea and liquid fish guts from a fertilizer company. We started soaking the charcoal in buckets on 2/17/2010 using these formulas: Urine - undiluted. Seaweed - 4 T to 1 gal. water. Fish guts - 4 T to 1 gal. water
2. On 3/17/2010, we removed the biochar from the buckets and shredded it in the compost shredder. We put the shredded biochar back in buckets except for a small amount that we used for the worm avoidance test.
3. On 3/17, we set up the worm avoidance test to find out if worms like our biochar soil. If worms like it, then probably plants will like it too.
4. Results of the worm avoidance test showed that worms liked the seaweed biochar and the fish guts biochar. The worms did not like the urine biochar. Because of these results, we rinsed the urine biochar to make it less strong. This is the biochar we will use in the plant growth test.
5. Biochar soil mix. We made soil mixes of 2 parts potting soil to 1 part biochar for each of the treatments.
6. On 4/7/2010, we planted collard seeds in 4 trays. There is one tray for each kind of biochar plus one tray of plain soil used for a control. We planted 3 seeds in each cell. We labelled the 6-pack containers.
7. After planting, we randomized the 6-pack containers by mixing them up and putting them in different trays. The trays will be watered and cared for over a one month period.
8. After one month, we will measure the size of all the plants and report on our observations.

Results of the Worm Avoidance Test:

Fish Guts
Worms in biochar
Worms in control

Results of the Plant Growth Experiment:

Measurement Procedures:
1. Find the 2 best 6-pak pots from each of the 4 treatments: seaweed, fish, urine and control
2. Divide class into 4 groups and assign each group to one of the treatment samples.
3. Each group should label their pots as follows:



4. Count how many plants are growing in each cell. Record the value.
5. Each group should get two large sheets of construction paper and write the labels across the top like this:

B1 B2 B3 B4 B5 B6

A1 A2 A3 A4 A5 A6

6. Then remove the plants, roots and all from the pots. Shake the dirt out of the roots and lay the biggest plant from each cell on the paper under its label.
7. Measure the height of each plant stem to the top leaf and record the value.
8. Measure the length of the root mass for each plant and record the value.
9. Measure the width of the root mass at its widest point and record the value.
10. Take a picture of the sheet of paper with all the plants.

Data Collection Sheet for Plant Growth Results:
Cell Label
Number of plants
Stem height
Root Length
Root Width













Compiled Results of Plant Growth Experiment Measured on May 12

Stem Height
Root Length
Root Width
Rinsed Urine
Fish Emulsion

1. What do the results say about each different kind of biochar compared to the other kinds of biochar?
Fish emulsion had the worst results; urine was best and seaweed was in-between. Urine probably has more nitrogen than the fish or the seaweed. Urine also has growth hormones that promote plant growth. Why did the fish do so badly? It has more nitrogen than seaweed, but we noticed some bacterial mats growing in the buckets where we soaked biochar in the fish emulsion. Perhaps these were bad bacteria harmful to plants. Or perhaps the bacteria used up all the nutrients in the fish emulsion. We did not observe bacterial mats in the seaweed biochar.

2. What do the results say about our biochar compared with no biochar?

It seems that our biochar inhibited growth of these plants, except when we used the biochar soaked in urine. The urine seemed to compensate for the biochar properties that inhibited growth in the other treatments. We were not expecting these results because the teacher’s homemade biochar had produced good results earlier. But the homemade biochar was much lighter than the BBQ biochar. We believe the BBQ biochar had a lot more volatile oils and tars remaining in it compared to the homemade biochar that was mostly just carbon.

Can the experiment tell us anything about biochar in general or just about the biochar that we made from BBQ charcoal?
The experiment tells us that the BBQ charcoal might not be good for starting and growing young collard plants. However, we used the same seaweed and fish emulsion biochar at a slightly weaker concentration (3 parts soil to 1 part biochar) for our plant sale plants – we transplanted seedlings of a variety of species (broccoli, leek, celery) into this mixture – and those plants grew big and healthy. So perhaps our biochar mix for the experiment was just too strong. We concluded that the experiment does not tell us much about biochar overall because there are so many variables involved.

What kinds of mistakes did we make in the experiment?
  • We did not control the number of seeds planted in each pot well enough. Some pots had too many plants.
  • We forgot to water a few times and the plants suffered.
  • We broke off too many roots when measuring the results so the roots measurements are not accurate.

If we did it again, what could we do differently?

We would have learned more if we had:
  • tried the biochar alone without treatments
  • tried the different biochars at different concentrations in the soil mix
  • measured the pH of the biochars to see if that was a factor

What other kinds of biochar could we test?

  • Biochar that we made with our TLUD stoves
  • Biochar that we pick out of campfire rings
  • Biochar we find in the woods left over from the big Biscuit Forest Fire
  • Biochar mixed with bokashi from our school compost