Now roots play some key roles in the life of plants they; anchor plants in the soil, are the engine for plant growth, provide access to water and nutrients, as well as storing energy and carbon…so what effect does biochar have on tomato root systems?

Observations from our Tomato Trial

As our tomato growing experiment came to an end we extracted the roots from the beds to see if the improvements we had seen above ground were somehow repeated underground. To our pleasant surprise, there were major differences. The roots of the biochar grown plants were substantially bulkier than the controls.

Control plant root on left, trial plant grown in biochar enriched compost on the right. The plants had been carefully removed from their growing bed and excess soil was removed by dunking gently in water.

Looking more closely we noticed that what appeared to be biochar particles adhered to the root system.

Section of tomato root decorated with biochar particles

We think it’s a thing of beauty and weren’t expecting such striking images.

Biochar particle on left with roots growing through the particle. Agglomerate on right also infiltrated by roots

The roots form quite a tangle but we could see examples where the root is growing directly into the particles of biochar.

We are not the first to see this. Lehmann and others have published photos showing roots interacting with biochar particles, see References below.

The Test – Are these particles Biochar?

The root system is decorated with particles, black particles. At first glance they look like the biochar we had incorporated into the compost used in our growing beds. To be sure we tested a section by crushing some of the particles under a small screwdriver blade ca 2mm width. The clear give-away for char is that it crushes with, often, a small “crack” before breaking into a pile of fine particles or dust – a brittle failure.

Among the pieces of char we did find some fragments, black on the outside brown and wood-like on the inside. These particles did not show the brittle failure of biochar but rather a plastic deformation under the pressure of the blade. The soil we used in the trial was created from garden compost sieved to 12.5 mm to remove larger material such as pieces of wood and stones. Woody fragments smaller than this were still present in our growing media.

Reflection – Root Systems Love Char

These tomato plant roots have formed an extensive network decorated with biochar and some woody fragments. Both biochar and these wood fragments are clearly not phyto-toxic. It is difficult to escape the conclusion that these “roots love biochar”. Reference 1 below includes the comment: “Our results indicate that roots are attracted towards biochar, resulting in its (N & P*) partitioning between bulk and rhizosphere soil. Biochar thus controls plant root nutrient acquisition directly as a nutrient source and indirectly by altering soil nutrient content.” Their reference* in the quote above is to nitrogen and phosporous.

It is difficult to draw too much from this small scale experiment but it deserves follow up in later trials.

References

Biochar–root interactions are mediated by biochar nutrient content and impacts on soil nutrient availability
M. T. Prendergast‐Miller M. Duvall S. P. Sohi
First published: 04 September 2013

“Our results indicate that roots are attracted towards biochar, resulting in its partitioning between bulk and rhizosphere soil. Biochar thus controls plant root nutrient acquisition directly as a nutrient source and indirectly by altering soil nutrient content.”

Rapid electron transfer by the carbon matrix in natural pyrogenic carbon
Tianran Sun, Barnaby D. A. Levin, Juan J. L. Guzman, Akio Enders, David A. Muller,
Largus T. Angenent & Johannes Lehmann 
Nature Communications volume 8, Article number: 14873 (2017)

Researchers discover high-def electron pathways in soil
by Cornell University
April 3, 2017

Contains a photo showing roots interacting with a biochar particle.