Today I was looking up the effects of wood ashes on soil, which led me to soil building in general. For most people, soil is just "dirt". It's not thought about too much and mostly to be tolerated. I think people do know there is "good soil" and "really good soil" and there are things we can do to it to help plants grow better, like buying a bag of steer manure at the big box store.
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As a long-time organic gardener, Rodale inspired from the times of the old magazine "Organic Gardening and Farming", soil for me has a more complex and living character. It's almost spiritual. I know there are no gods. But there is soil.
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There are a lot of ways to look at soil. Soil is physical structure, it's chemical constitution, it's history, it's a community of organisms, it's process.
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I try to build all of those aspects to promote health of the garden plants and trees.
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For structure, I'm using raised beds, and compost. Raised beds help structure by creating areas that are not walked on, and don't need tilling. Walking causes excessive compaction, especially when wet. Tilling causes compaction under the tilled area, and breaks up fungal fibers that support soil structure and transportation of nutrients through soil levels. It also breaks up tiny tunnels left by old roots, worms, and tunneling insects. Tilling has a place, but the raised bed method minimizes the need for tilling, and supports the soil structure. Compost makes the soil more spongy, allowing more water in when dry, and promoting better drainage when wet. I also mulch, which prevents formation of a hard crust on the soil surface.
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For chemical constitution, again I'm adding compost. When you think about it, compost is the plant material that grew by removing nutrients from soil, so using compost adds it back. What's added back is exactly what plants need, because it the chemical part of what plants are. Plus compost contains beneficial bacteria and fungi, that may have been disrupted or depleted in the original soil. I also add crushed eggshell for calcium. That may not seem like much, but it adds up over a year's use of eggs. As for wood ash, care is needed. I haven't chemically tested my soil. I assume it's somewhat acid, given that blueberries do well here. Blueberries don't thrive in alkaline soils. Wood ashes alkalinize soil, so can be used in limited amounts to return nutrients to acid soils, but I wouldn't use in alkaline soil.
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I don't know much of the history of my soil. There is volcanic contribution. This land is former Fir forest. It was logged, long ago. Part of it was orchard - there might be residual chemical residue. Given that is remote past, I hope not much. Most of the soil for the raised beds is coming from an artificial hill behind the house. I don't know the history of that hill - it's odd. I'm suspecting it's fill from the house, or from digging the septic tank and drainage field. Lots of mushrooms are coming up now that it's fall. That suggests an active fungal population. I avoided using soil from below the septic tank drainage field, assuming some household cleaners or other substances may have wound up there.
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As for the community of organisms, all of that digging, moving, and mixing, must have caused tearing up of the fungal microfibers, but otherwise I think the compost supports bacterial, fungal, worm, and beneficial insect community. I'll try to give the soil a chance to recover it's communities. I bought some mycorrhizal inoculant to promote plant-fungal interaction. There is no proof that helps so I don't know. The local fungal spores might be all that's needed. When I plant beans and peas, I'll add rhizobium inoculant too. Rhizobium enables legumes to convert atmospheric nitrogen to forms plants use, promoting growth and enriching soil. Rhizobium can be specific to the type of legume, so most likely there isn't the right type, if any, in my soil. There were earthworms in the compost and in the soil added to the beds, so I think I'm good there.
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Most likely, I think too much about these things. Ramble while having morning coffee. The grounds of which, will go into the raised beds too. Coffee grounds are an excellent addition to soil or compost.
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Embedding links isn't working, so here are some sources. I'm not promoting any particular product, but a couple of these are sources I've used.
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http://gardening.about.com/od/soil/a/GardenSoil.htm

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http://organicgardening.about.com/od/soil/qt/coffeegrounds.htm

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http://www.territorialseed.com/product/127/22
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http://www.thehydrosource.com/pure-mycorrhizal-inoculant.html
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http://www.rodaleinstitute.org/node/441