Here is a link to a very interesting theory about the use of woodchips in USA. It is called “The Back to Eden Concept”.
It is claimed here that Woodchips can adapt the PH of the soil to the plants needs and increase their sugar content on a year by year bases. Perhaps there is some type of trasmission system inherent within the wood of the woodchips. This definitely needs looking at in a university scientific level.
In our experiences with woodchip mulch we have had really good results from bulbs to trees, as well as crops. Also in our recent experiment with more unusual root crops woodchips had been very useful in getting around the problem of the need for constant cold in the winter, but with no frost but with light – such as with Oca and Yakon.