Before-and-after nutrient test on two patches of soil

On a recent weekend I did two soil-texture tests in my backyard which graphically illustrate the value of a soil-building program. The first, using soil taken from an established vegetable bed, tested out at 60 percent sand, 40 percent silt, and 0 percent clay. The US Department of Agriculture (USDA) describes such soil as sandy loam and considers it moderately good for crop production.

The second test, using soil taken from a neighboring grass patch, can be considered representative of the entire garden before the soil-building program began. The USDA would be less complimentary about that sample. It tested out at roughly 85 percent sand, 15 percent silt -- just a skip and a hop away from being pure sand. It is too well drained to be good crop-producing soil.

Nutrients leach rapidly away from plant roots and, for the same reason, even short dry spells can result in moisture stress.

What turned the poor soil into moderately good soil in my vegetable garden (it still drains too readily to be perfect) has been nothing more than the annual addition of organic materials.

But back to the soil-texture test. It's a very simple thing to undertake, and you might wish to test your own soil this way.

I got the idea from a useful publication, edited by Sharon Ross, called Family Food Garden. All you need is a quart jar, some water, and a little garden soil. Fill the jar about two-thirds full of water and add the soil until the water comes to within half an inch or so of the top. Screw on the lid and shake vigorously for a minute. Now set the jar aside and leave it for a few hours.

The heavy sand in the soil is the first to settle and does so at the bottom of the jar; next comes the silt; and finally the clay. The three stratified layers are clearly visible in good light, and you can roughly gauge the percentage of each in your soil's makeup. According to Family Food Garden, the addition of a dispersing agent to the quart of water will aid the stratification. But for the average gardener the test is accurate enough without the agent.

Loam is considered to be the best of all soil types. According to the USDA, loam consists of 7 to 27 percent clay, 28 to 50 percent silt, and 20 to 45 percent sand, with the best of all loams falling in the middle of these percentages. The trouble is, few people are blessed with naturally good soil. On the other hand, good soil can be built.

If you don't have naturally occuring clay or sand in your soil, there is nothing much you can do about it short of trucking in expensive loads of the stuff. Fortunately, you don't have to go to such extremes. Organic matter works wonders with all soil types, except perhaps muck soils, which are of almost total organic origin anyway.

In my yard the addition of organic matter has boosted the siltlike content of what would otherwise be almost pure sand. This has improved the texture and moisture-holding capacity of the soil. On the other hand, the silty humus material that comes from addign organic matter also improves clay soil -- by opening it up and providing much-needed aeration. In short, the organic matter helps make up for the absence of either clay or sand in your soil.

Organic matter -- leaves, hay, straw, weeds, kitchen scraps, manures, etc. -- does more than improve soil structure. It also provides the nutrients for the next generation of plant life.Basically, the nutrients that went into the growth of the plant are returned to the soil when the plant decays with the help of an army of bacteria, fungi, and other creatures of the earth, such as earthworms.

Fall is one of the best times to incorporate organic matter, because the soilis warm at this time of year, even whn air temperatures are frigid. In such a cozy situation the decay organisms are most effective. They get a head start in converting the organic waste into nutrient-rich hunus, which will both feed your plants next spring and improve soil tilth.

Fortunately, too, organic materials are at their most abundant in the fall.

In a samll garden, the organic matter can be turned into the soil with a garden fork or spade. Otherwise, rent a tiller for a thorough and speedy job. Spread the materials about 6 inches thick and dig in. Another option is to dig a trench 6 to 12 inches deep and as wide as you want the bed. Fill this with the waste materials, then put the soil back on top. This is hard work, but many gardeners say it works.

In soil that has been built up over the years so that it has adequate drainage, you might apply the organic materials as a mulch, leaving the earthworms and other soil organisms to incorporate it slowly into your soil.

In any event, it is beneficial to mulch your garden over winter, even if you plan to turn it into the soil as soon as spring comes around. In recent years, I have gone the permanent nulch route and the results are proving most satisfactory.

If you can shred all these waste materials, using a power shredder or a rotary lawn mower, they will break down much more rapidly. Shredded materials also make for a much more attractive mulch.