the wood ash will just take the place of the dolomatic lime.

"Field and greenhouse research have confirmed the safety and practicality of recycling wood ash on agricultural lands. It has shown that wood ash has a liming effect of between 8 and 90% of the total neutralizing power of lime and can increase plant growth up to 45% over traditional limestone." http://hubcap.clemson.edu/~blpprt/bestwoodash.html