I've been dabbling in no-till techniques for the last few years, due to a vague understanding that tilling is bad for the soil.  Robert Kourik's book gave me the low down on the best no-till techniques and why they succeed (or fail.)

So, what's wrong with tilling?  Although we can't see it, our soil is teeming with microscopic and macroscopic life, most of which lives in the top three inches of soil.  Tilling churns up soil, mixing the microorganism playground with the lower soil and resulting in a lot less life.  Although you might expect that the microorganisms folded deeper into the earth just expand their populations, lack of air and sun quickly kills them off.

Bare soil is another bane of conventional tilling.  Erosion is the obvious problem --- rain washes away the precious topsoil when it is unprotected by plants or mulch.  But sun is just as much of a problem.  When bare soil is exposed to summer sun, the heat vaporizes nitrogen and kills the precious soil microorganisms, resulting in a garden that requires much more fertilizer in order to grow your veggies.

Of course, we can't just throw our lettuce seeds amid the grass in our lawns and expect it to grow.  So how do we garden without annual tilling and bare soil?