Paul and Sandra,

Replenish your soil from the top down the way that Mother Nature does in a woodland area. Here's what I mean: When you walk through a wooded area, what do you see on the surface of the ground? Leaves, sticks, twigs, rotting logs, stumps or branches, dead grass and other plant debris. Does anyone come along and rototill that stuff into the ground? No.(Well, in an odd way....you might have an occasional armadillo or skunk digging and working some of the surface debris into the ground.) What does occur, though, is that over time rain and small decomposers in the soil (earthworms are the most well-known, but there are many others) carry the nutrients down into the soil. So, as long as you regularly apply mulch or other material like manure, blood meal, etc. to the soil surface, it will decompose on its own and, as it breaks down, release nutrients into the soil.

You really don't have to work it into the soil manually, unless you just want to, in most cases.

There is an old saying, though, and it is this: "Heat eats compost" and, for the sake of discussion, I am using the word "compost" to refer to any organic (once-living) material in the soil, so it would include humus, plant debris, etc. In a hot climate like ours you have to continually add organic material because it decomposes very quickly in our long, hot, and often humid summers. It is preferred to add the material to the soil surface and let natural decomposers work it into the ground. Why? Because when you work organic material into the soil, whether by hand or by tiller, you are adding oxygen to the soil and oxygenation speeds up decomposition. (This is one reason you stir or turn over working compost--to speed up its rate of decomposition.) One of the relatively new techinques in farming is no-till farming and farmers are doing it because it works. They plant their new crop through the 'debris' of last year's crop (with some exceptions) and this cuts down on the loss of organic material in the soil due to oxygenation and it cuts down on wind erosion and, often, rain erosion as well.

I know from working with my soil that I really need to "feed" it every year by adding mulch (non-stop) that will decompose and feed the soil. Depending on where you live, you may not have to add it that often.

If you know of someone who has a mulched area where mulch has been for several years without being disturbed, and where they add new mulch on top of the old mulch on a regular basis, dig down into that mulch. On the surface, it will look like chunks of bark mulch. The lower you go, the more you'll find it has broken down into compost.

If you cannot tell by looking at your soil whether or not it has adequate organic content, do the jar test linked below. I do it all the time to check various parts of the garden because I have some areas that are more clay-ey and others that are more sandy. For what it is worth, my sandy areas seem to need more frequest amending, but then they are pure sugar sand, so I guess no matter how much organic material I add, it just isn't enough.

You can add whatever organic material you want to your soil. If you use manure, it should be completely composted first to reduce the incidence of sprouting weed seed and to reduce the chance live bacteria, like E. coli, will contaminate your plants. Or, you can use chopped and shredded deciduous leaves, rotted/spoiled hay/straw/grass clippings, purchased compost or humus, cottonseed hulls, etc.

As far as nutrition, you need to regularly put some nutrients back into the soil to replace what your plants take out of the soil. You can do this in several ways. First, if you are using a lot of native plant material (leaves, grass clippings, etc.) as mulch, they'll put the nutrition into the soil as they decompose. Or, you can use any of the organic fertilizers--blood meal, bone meal, earthworm castings, soft rock phosphate, green sand, lava sand, etc. Or, you can purchase a good organic fertilizer that contains all the trace elements as well as the major elements, and of the ones available, I prefer Espoma Vegetable-Tone for general veggie gardening or Espoma Tomato-Tone for tomatoes, peppers and eggplants. Or, you can use slow-release chemical fertilizers found on the shelf at any store that carries lawn and garden supplies. If you do this, be sure you get a fertilizer that is a fertilizer intended for food crops if you're growing food, and avoid weed-n-feed combos.

And, for what it is worth, tilling up or digging up the soil will not keep reseeders from reseeding. In fact, tilling or digging up the soil often gives you more sprouting seeds, but the problem is that such activity stirs up buried weed seeds by the millions--and that is another argument against disturbing the soil.

Even though I think manure is great, I only use it every 2nd or 3rd year in any given bed. It is better to give your growing beds a wider variety of amendments that put more types of nutrition into the soil. However, if I had a perpetual source of free, composted manure, I'd use it most of the time. Manure and leaves/grass clippings used together will usually give your soil all it needs as long as its nutrients are not terribly out of balance.

One way I work to improve my sandy soil (and I only have a narrow band of it about 30' wide, running north-south through our property of mostly thick, heavy, red clay) is to add clay to it. I usually add a couple of inches of clay by rototilling it in when I am about to plant an area....say, if I can converting a piece of lawn area to a planting bed. This only works, of course, if you have access to clay, which I do. Clay is high in mineral content so it adds to your soil fertility and it helps the sand retain moisture much longer than sand holds moisture alone.
I hope this answered your questions.

Dawn

Here is a link that might be useful: Jar Test for Soil Texture/Composition