How to improve 'pore space' so soils can store goodies

When I first started gardening on the coast of Massachusetts, it was obvious that the soil lacked the quality needed to grow vegetables intensively. Simply, it was far short of the 5 percent organic matter that is considered ideal for productive food growing.

For the record, good garden or farm soil is 50 percent ''pore space,'' which provides the storage for the moisture and air needed by plant roots.

The solid portion of the soil is 45 percent mineral deposit, derived from the original parent rock, and 5 percent organic matter in various stages of decay. It doesn't matter too much if the organic content increases by a few percentage points, but soil quality declines rapidly as organic matter drops below the ideal fraction.

Both heavy clay soils and light sandy soils need their organic fractions increased.

My garden soil was just too sandy. So for the first few years, I spread leaves several inches deep over the garden each spring, sprinkled a little chicken manure on top, and turned everything in with a rented Rototiller.

The soil responded in a gratifying way as the increasing humus content bound the mineral fractions together into little ''soil pebbles,'' the crumb structure that indicates a good soil. Water was absorbed more readily and retained more readily than previously.

I have since learned two things about this particular practice: (1) that it would have been more beneficial had it been done in the fall; and (2) that not all soils can immediately accept large quantities of organic matter.

Since the practice of tilling organic matter - leaves, straw, garden refuse, and such - into soil has spread, some problems have also surfaced.

Organic matter is being plowed into some soils and failing to decompose rapidly, often turning into a sour mess. Apparently this is occurring on land that has been deprived of its biologically active topsoil by erosion or construction practices, or on land subjected year after year to an exclusive diet of chemical fertilizers and herbicides that has destroyed much of the soil life.

Put another way, these abused soils have lost their ability to readily digest the organic matter that is fed to them.

If your soil is capable of decomposing organic matter (you can assume your soil has this capacity if earthworms are present), simply spread the organic matter, including manure if you have it, over the soil and turn it in. In the relatively warm soils of fall, decay will begin immediately, taper off during winter, and resume again in the spring.

Not only will the organic matter provide plant nutrients as it goes through the final decay process the following growing season, but it will also lock up many soluble nutrients during winter.

The addition of a mulch over the surface of the soil will also help soil structure.

In fact, once their soils have reached a satisfactory state, many gardeners find they can rely solely on continuous mulching to retain a good-quality soil.

Mulching, with cover cropping where possible, is now my preferred way to go.

Where does all this leave the gardener with biologically poor soil?

The need still is to incorporate organic matter quickly into the soil. There are two options:

* Use partly predigested materials, such as compost or manure.

* Sprinkle the necessary bacteria and enzymes (generally available from garden centers in powder form) over the organic matter before turning it into the soil. The one product that I have tested and found satisfactory is called Winterize.

Soil building can be undertaken at any time of the year, but the best of

all seasons is fall.