Dream-Team: Activated vegetable charcoal and Trichoderma as soil conditioner

Vegetable carbon, also called biochar, is a porous material that is used as a soil improver in gardening, landscaping and agriculture. It is a charred product, which is produced from vegetable substances (such as wood, grain husks, garden waste). Carbon-enriched Biochar is not a nutrient, but a habitat for desired microorganisms.

The European Biochar Certificate (EBC) has established itself as the quality standard. Many countries use this standard for the biomass used, the production technology, the properties of the coal and for its application.

Only activated vegetable carbon improves the soil

Biochar used by itself is not effective immediately, as all living organisms are killed during the heating process (500-800 °C). A direct application of biochar to the soil can have negative effects, since the charcoal must first “charge” itself with nutrients and microbes. This can be done, for example, by mixing it with compost or organic fertilizer. Only enriched and saturated biochar is a real soil improver. Without enrichment, biochar can raise the pH value of the soil and immobilize nitrogen, causing micronutrients to become less available to the plant. When enriched, biochar makes a valuable contributions to soil and plant health.

Advantages of carbon-enriched biochar

  • Plant carbon matter can store water up to 5 times its own weight and thus supports the soil organisms as well as the living plant during drought stress
  • Carbon-enriched charcoal can buffer nutrients and make them available to the plant when needed, thus counteracting soil leaching.
  • The porous structure of vegetable charcoal leads to higher soil aeration and supports the loosening of heavy soils. This prevents soil compaction.
  • Binds odours: heavy metals such as copper and toxins (excretions of harmful fungi) and thus promotes soil diversity and reduces microbial toxins.
  • Increases humus content and soil fertility
  • Soil bacteria and microorganisms can settle and multiply in the pores of the biochar. Organisms, such as Trichoderma, are maintained by biochar over a longer period of time in larger populations in the soil. The frequency of application can thus be reduced.

Trichoderma grows on biochar

A study by Empa (Ribera et al., 2017) showed that Trichoderma atrobrunneum can rapidly colonize the substrate of biochar. After 48 hours (at 25 °C), the entire surface of the biochar was populated with Trichoderma (see Figure 1). The different modes of action of Trichoderma atrobrunneum further enhance the activated biochar.

Figure 1 A and B: Colonization of biochar (appears black in the photo) by Trichoderma atrobrunneum (appears green in the photo). Scaling is 100 micrometres. Source: Ribera et al., 2017.

The perfect team: Biochar and Trichoderma

The frequency of Trichoderma application can be reduced by biochar, as the biochar maintains the population of Trichoderma in the soil over a longer period of time. Thus, the stimulation of the growth of roots and plants and the parasitization of harmful fungi by Trichoderma is guaranteed for a longer period of time.

Figure 3: Hyphae of Trichoderma atrobrunneum coils around the hyphae of a harmful fungus, eventually dissolving it by means of enzymes.

Tests carried out together with FiBL (Research Institute of Organic Agriculture) have shown that nutrient-poor soils are positively influenced by a combination of Trichoderma atrobrunneum and biochar (see Figure 2). This was shown  by the increased availability of phosphorus and iron in the soil.

Figure 3: Influence of Trichoderma atrobrunneum on the amount of available phosphorus in the soil after 3 weeks. K1: Control, T1: Trichoderma atrobrunneum, B1: Biochar, TB1: Trichoderma atrobrunneum plus biochar (Fuchs & Tamm, 2018)

Activated biochar for healthier trees – Stockholm as an example

The majority of the trees planted in Stockholm have lost vitality over the past few years, with leaf fall occurring as early as July. Tree care specialist Björn Embren from the Road Traffic Department used a mixture of granite gravel, soil and biochar for new plantings. His findings are enthusiastic: “We are impressed with what Stockholm’s city forest now looks like, with every single tree now having a denser crown”. Since 2009, at least 2,000 trees in Stockholm have been treated with carbon-enriched biochar.

Literatur:

Fuchs J, Tamm L. 2018. Wirkung von Trichoderma atrobrunneum (vormals harzianum) Stamm Th720 und Biochar auf Pflanzenwachstum. Frick.

Ribera J, Gandia M, Marcos JF, del Carmen Bas M, Fink S, Schwarze FWMR. 2017. Effect of Trichoderma-enriched organic charcoal in the integrated wood protection strategy. PLoS ONE 12: e0183004.