Lydia, very nice question . Physical qualities of biochar depends upon the temperature of decomposition , and the composition of waste material undergoing decomposition. However , pH , EC and carbon concentration , all increase with rise in decomposition temperature . There is also a rise in C:N ratio due to increase in carbon concentration  and reduction in n content with rise in decomposition temperature.   CEC tend to reduce with rise in temperature during biochar formation , primarily due to reduction in calcium concentration . find below the PDF giving you more details .

Thank you very much for your time and the suggested paper. I will read this and maybe come back to you for more questions!

Some points of clarification:

EC should be closely related to total concentrations of salts (and all electrolytes), but CEC is the capacity of the material to hold exchangeable cations.  There is thus no fundamental reason for there to be any link between EC (or pH) and CEC of chars.  While there may be an empirical relationship between EC, pH, and CEC for certain types of chars (made from certain feedstocks under certain pyrolysis conditions), you cannot safely infer one from the other.

Thank you very much Prof Thomas!  Yes i fully understand the link of EC and salts/electrolytes as it makes sense, my results show that.

pH relates with high Alkali and Ca contents (feedstock influence thus) that i also believe is reasonable.  Indeed the influence of process conditions (technology of biochar production) and feedstock itself is vey strong,