Carol Bovenaer, age 12, Winston‑Salnm, N.C., for the question:

What is soil?

Soil is a vast grocery store which feeds the plant world. And the animal world depends on the plant world for its food and its oxygen. So the soil is vital to all life on land. It comes in different qualities and covers vast areas of the earth in layers from a few inches to a few feet thick. Soil making is a slow process and nature may need 100 years to make a layer of it one inch thick.

It is true that green leaves make plant food from air, sunshine and water. But, as a rule plein wr for will not o. A growing plant needs certain vital chemicals dissolved in the water which seeps in through its roots. A good soil is rich in these chemicals and always ready to dissolve them in ground water and then build up this rich moisture to the roots of plants.

The bulk of all soils is powdered rock. But powdered rock will not support plant life. It must be mixed with a plentiful supply of organic matter. And organic matter comes from the world of living things. It may be decaying plants, fallen leaves and rotting tree stumps. It may come from the waste material from animals or from their dacaying bodies.

Also present in the soil are countless bacteria. These mites attack the fallen vegetation and animal organic matter and cause them to decay. And decay is a vital process in the making of soil. It breaks down orcanic matter into simple chemicals. And those chemicals are the ones needed by new enscrptions of plant life. In time each generation of plant and animal life falls to the ground and decays, building up its vital chemicals to new generations.

When the harvest crop, we remove the plant life which would otherwise decay and return its chemicals to the soil. In growing one bushel of wheat takes from the soil two pounds as of nitrogen, one pound of potassium and almost half a pound of phosphorus, besides other chemicals. Then the wheat is harvested and carried away the soil is in no condition to feed a new generation.

The farmer must see to it that this loss of vital chemicals is replaced. He may decide to replace the nitrogen with a crop of peas. For the roots of pens and other legumes support bundles of little bacteria which spend their time putting nitrogen into the soil. Other chemicals may be replaced with fertilizers.

Soils vary and the up‑to‑date farmer knows just whet will grow best in his soil. He knows whether it is to acid or to alkaline and how to correct it. He knows about the profile of the soil, its different layers. On the surface is the topsoil which feeds most of his crops. Below the topsoil is a layer called the subsoil.

Rain water seeps through the topsoil try the subsoil below. It carries with it dissolved chemicals stolen from the topsoil. So the farmer plows, turning the richer subsoil topside where his crops can use it. In nature, the subsoil is carried upstairs by countless busy helpers. Moles, rabbits and all burrowing animals turn up a good doe of subsoil during a year. But the bussiest of all natures plowmen is the little pink earthworm.

In arid regions, the topsoil may be richer than the subsoil. This is because chemicals are pulled up by evaporation from below a desert surface often needs only water to become very rich topsoil.