- Particle density and surface area depend on the porosity.
- A high porosity, low density biochar may have higher water holding capacity, but it may be more easily removed by wind or water.
The physical and chemical properties of fresh biochars
Important physical properties of fresh (and aged) biochars include:
- Bulk density and particle density, particle size, macro and microporosity, surface area, water holding capacity.
The chemical, electrical and magnetic properties include:
- Macro nutrient content (N, P, K, S, Ca, Mg) and micro-nutrient content (Fe, Mn, Cu, Zn, Mo, B, Cl, Si, Na, Ni ). Measuring their solubility at different soil pH will provide an indication of their plant availability
- Soluble organic compounds (soluble in water or in other solvents)
- pH (proton activity), Eh (electron activity), EC (electrical conductivity), liming value, cation and anion exchange capacity (CEC and AEC), reducing and oxidising potential, magnetic susceptibility/paramagnetism
- Adsorptivity of heavy metals and organic pollutants.
Physical properties of biochar: General
Physical properties of biochar: Density
Physical properties of biochar: Macro and micro-porosity
Physical properties of biochar: Porosity, surface area
Physical properties of biochar: Porosity, surface area, bulk density
Physical properties of biochar: Hydrophobicity
Properties of biochar: Grindability
Chemical properties of biochar
Proximate vs. Ultimate Analysis
Relationship between Fixed Carbon, Ash and Volatile Carbon
Relationship between C, H, O for fresh biochar
Properties of fresh biochars: Persistent carbon
The Composition of Biochars
H/C ratio – examples
Soluble and Mineralisable carbon
Polycyclic Aromatic Hydrocarbon (PAH)
Polycyclic Aromatic Hydrocarbon (PAH) content
Properties of fresh biochars: Mineralisable carbon, Key points
Properties of fresh Biochars: Ash (Inorganic Compounds)
Properties of fresh Biochars : Heavy metals
The Availability of Macro Nutrients in Biochars: Fertiliser Value
Matching fertiliser value to crop requirements
Cation Exchange Capacity
Anion Exchange Capacity (AEC)
Overview of trends of properties with temperature and residence time
The impact of biochars in soil and composting
Plant Available Water
Review of the literature indicates that grasses and straw biochars provide the greatest increase in plant available water
Electrochemical Properties Of Biochars
Electron activity, Redox effects
Biochar makes oxidised soils more reducing. It lowers the Eh (electron activity) and increases the pH. This helps plants and microbes resist stress e.g. increase in temperature.