Be aware that biochar, depending on the feed stock and process, is more than a sorbent/exchanger: it is alkaline and contains potentially beneficial constituents such as Ca, K, P and reactive Si. These constituents interact with the soil and may affect its suitability as a plant growth medium. When the biochar amendments are at % concentrations the changes can be appreciable. To attribute the effects other than to 'biochar' is not simple, but corresponding inorganic amendments are a start as 'control' treatments. Otherwise the wider applicability of results is unpredictable.