A four-year independent trial by Terra Nostra (Netherlands) compared Carbon Gold Tree Soil Improver mixed with structural tree soil (“Amsterdam Tree Soil”) against plain biochar and against a structural-soil-only control. The trial was designed and conducted by Terra Nostra’s scientific research department.
The results published by Terra Nostra are summarised below, with the original Dutch source available here.
Trial design
Terra Nostra researcher Wendy Batenburg tested three different batches across the trial programme:
- Reference: regular “Amsterdam” structural sandy soil (coarse sand, uniform grain size greater than 400 microns)
- Plain biochar mixed with Amsterdam structural soil
- Carbon Gold enriched biochar with mycorrhizal fungi and natural mineral components, mixed with Amsterdam structural soil
For each batch, ten 1 m³ samples were placed in big bags. A two-year-old small-leaved lime tree (Tilia cordata) was planted in each. In total 30 lime trees were tested over two years, ten per batch.
Measurements
Above ground:
- Stress levels and tree vitality, measured with a chlorophyll fluorescence meter
- Degree of degradation, shoot length and leaf density
Below ground:
- Soil nutrient value (CEC value) at start and end
- Root size and root development
- Mycorrhizal fungi growth
At the end of the two-year measurement period, all 30 lime trees were uprooted with roots intact. Roots were sorted into four diameter classes (under 2 mm, 2 to 5 mm, 5 to 10 mm, over 10 mm) and totalled per tree and per batch.
Reported results
Terra Nostra reported that the enriched biochar mixture produced the strongest outcomes in the trial.
Above-ground findings:
- More growth from year one
- Less stress and higher leaf vitality
- Lower susceptibility to lime leaf wasp larvae compared with some other batches
Below-ground findings:
- Soil nutrient value (CEC) in the enriched biochar mixture decreased by 11% over two years, compared with a 40% decrease in the reference mixture
- The strength of the enriched mixture was preserved, an important criterion for planting sand
- Root development was substantially greater: 1,028 metres of roots per tree in the enriched biochar mixture, compared with 706 metres per tree in the reference mixture. Approximately 98% of the additional root length was made up of fine roots under 2 mm diameter
Conclusions reported by Terra Nostra
Source: Terra Nostra PowerPoint presentation:
- Better growth from year one
- Less stress and more leaf vitality
- Reduced susceptibility to certain diseases and decomposition
- More efficient use of nutrients
- Better root development
- Positive effect on soil life
What this means for UK tree planting
Tree pit specification is a long-standing professional concern. Urban planting projects routinely face high first-year mortality, and the Terra Nostra trial supports the use of enriched biochar within structural tree soil as part of a soil specification designed for root establishment.
Carbon Gold supplies Tree Soil Improver and Tree Fertiliser into UK trade and professional markets including arboriculture, landscape design, urban greening and tree planting projects.
Find Out More
Substantiation references: Terra Nostra four-year independent trial, designed and reported by the Terra Nostra scientific research department (Wendy Batenburg, lead researcher). Source: published Dutch summary at henrykuppen.nl and Terra Nostra PowerPoint presentation. Carbon Gold can provide the trial summary on request.
