Lower temperatures in biochar production (350-500 C) results in more "functional" groups. These groups provide the char with a higher negative charge. These chars adsorb much more positively charged ions than char produced above 600 C and have a much higher CEC (cation exchange capacity). The positively charged ions in question happen to be the majority of macro and micro nutrients necessary for plant growth and health.

Higher temp chars are more hydrophobic, have less negative charge and therefore less CEC.

The functional groups provide sites for microbial colonization as well so they increase the "life holding capacity" of soils. Further increases of these functional carboxylic (-COOH), phenolic (-OH), lactone (C(O)O-{carbon chain}-OH), and carbonyl (C=O) groups occur if the char is exposed to steam while still hot.

Steam oxidation at 400°C for 2 hours can nearly double the CEC of biochar compared and significantly increases the concentration of functional groups on the surface.