Food-producing plants on farms and in gardens sometimes suffer badly from prolonged drought while sitting within reach of plenty of water. The crops literally die of thirst when life-saving moisture may be only inches away.

The reason is that the roots cannot get to the water that is just below them. It may be the soil is too acid or too infertile for the roots to survive; it may be due to the hard pan (a layer of compact soil) the roots cannot penetrate. In either case, it can be corrected, and in many years will pay big dividends.

For example, 1977 a plot of soybeans in North Carolina barely noticed the midsummer drought that gripped much of the area. They went on growing despite the reinless skies.By early August they wer hip-high and loaded with young seed pods.

Neighboring soybeans were barely knee-high.

Only one practice - subsoiling - explained why these lush soybeans could be growing amid all the drought-stunned acres of the Coastal Plain.

Subsoiling has been under study by a team of scientists with the North Carolina Agriculture Experiment Station for the past three years.

Many soils in the area have a compacted layer due mostly to traffic - tractors and farm implements - moving across the land. The roots cannot penetrate it. They reach it and just spread out. When a drought comes, they are dependent on the top few inches of soil for moisture.

To break the hard pan, Dr. Eugene Kamprath, N.C. State University professor of fertility management, and his co-scientists, ran a subsoiler 14 to 16 inches deep under each row of their experimental soybeans at planting time. This freed the roots to move as deep as necessary to reach moisture.

In Maryland, most cultivated soils usually have a depth of at least 30 inches. These soils are capabale of having five to seven inches of water available to plants growing in them. In many areas, much of this water cannot be used by the plant. The great bulk of the roots are in the upper horizons, especially the plow layer.

It is mainly because the subsoils are not chemically conducive to root growth, according to specialists. Acid conditions and low fertility prevail and root development is retarded.

Then too, compaction inhibits the penetration of roots deeper into many soils. Both natural and artificial root restricting horizons are present in some soils, the specialists say.

For a crop such as corn this means the upper 12 to 18 inches of soil must supply most of the necessary water. Once this reservoir is depleted, growth is slowed or halted until rainfall can recharg the water supply. If the condition is prolonged, serious yield reductions or corp failure can results - all this when water is still available below the root zone.

Scientists at the University of Maryland found that applying lime, fertilizer and organic matter to the lower depths solved the problem.

Gardeners can accomplish the same results by double-spading. It must be done with mixing much of the subsoil with the surface soil, otherwise the texture of the surface soil may be destroyed.

Start spading at one end of the plot by removing a 3-foot strip of soil to a depth of 12 to 15 inches. Pile the soil to one side. The spade the subsoil inches deep and mix organic matter (peat, compost, rotted manure), lime and 5-10-5 fetilizer within. Do a thorough job of mixing. Use about 2 pounds of ground limestone, 2 pounds of 5-10-5 per 10 square feet (5x2) and 2 or 3 in layer of organic matter. Better still, have your soil tested and follow the recommendations. Replace the top layer of soil and then do another 3-foot strip. Keep it up until the job is completed.

Be extra certain the organic matter is mixed thoroughly with the soil. A mat of organic material can block movement of water and air between the surface soil and subsoil.

The treatment should solve the problem for four or five years.