Why? The research is showing some of the carbon is staying in the soil for 100s of years. If you would visit redrok dot com you would see that other design methods exist, and they have been demonstrated to generate higher tempratures. While 'excessive wood' exists, wood is a limiting factor for CO2 to Carbon char. Using crop wastes as the source of bio-char increases the CO2 to Carbon conversion ratio. Not to mention killing various things that effect plants which might be 'hiding' in the crop waste. Don't discount the use of the outgasing material as a way to generate power via stirling or internal combustion engines. wood gas was used during WWII as a substute for harder to obtain gasoline. Generation of units with a low enought cost, high enough heat and ease of operation while avoiding the known carcinogen effects of the resulting tars will be the engineering challenge.