One of the things that bubbles up from time to time as an alternative to our fumigation regime is the use of biochar, which is organic material burned at very high temperatures - ie charcoal.  Never paid it much mind because there is so much else going on and things to do, but the work by Diedre Griffin up at UCD and the subsequent concise summary of it is all I need to know.

A summary for berry people (link below for full article, it's only a few minutes of reading):

1- Biochar has been shown to increase (as in more alkaline) pH and fertility in weathered tropical soils.  The effect seen in tropical soils might not be the same up here in California.

2- Addition of biochar is an irreversible decision, but even so to maintain the benefit it might need to be repeatedly applied over time.

3- The effect of biochar doesn't kick in until the second year.   It's hydrophobic and consequently doesn't interact initially with the soil so well.

4- Rather than an effect on N cycling, it seems that the biochar  in the study had a positive effect on P, K and Ca.  All three of which most of our soils have in great abundance, so I'm not seeing the benefit for many of our soils on the Central Coast.

Nice piece of work here, I really appreciate the good research and straightforward summary.  Thank you Diedre.

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=22954