Joni Weick, age 9, of Tucson, Arizona, for her question:

Is it true that worms are good for the soil?

Soil is that crumbly, brown dirt in the garden. It is the rich, brown wound under the grass and the fields, the woods and the orchards. The plants need the soil and we need the plants. And the little pink earthworm helps to make the soil and to keep it just right for the plants.

We feed on leafy vegetables and crisp salad greens and these plants must grow in rich, brown soil. We eat eggs and dairy foods. The chickens that give us eggs and the cows that give us milk feed on corn and grains that come from plants that also grow in the soil. We eat meat from cattle, sheep and pigs that feed on plants that grow in the soil. If the earth lost its layers of soil there would be no plants and we would be very hungry very hungry people indeed.

Soil is made from powdered rocks and stones mixed with other things. Stormy winds and icy frost chip away pieces from the hard boulders and the bare mountain peaks. Rains and running rivers smash and bash the rocky pieces to powder and strew layers of the mud on the plains and in the valleys. The mud mixes with fallen leaves and rotting logs, dead insects and decaying animals. And this mixture becomes soil for new growing plants. It takes Mother Nature about 100 years to make a layer of soil one inch deep.

Through the ages, the rich soil piles up deeper and deeper. But many things must be done to keep it just right for the plants. It must be kept loose and crumbly so that air can filter down through tiny pores and pockets. It must be kept moist, so that plants can soak up water through their roots. As the rain seeps through the ground, it carries down the plant food chemicals. The soil on top has less plant food than the deeper layers. So we must dig up the deeper soil and put it on top.

The farmer does this when he plows his fields. But nature has a little plowman who depends all his life turning over the soil. He is Mr. Pinky, the earthworm. The little fellow feeds on old leaves and other bits of vegetation decaying in the ground. But he does not bother to pick aut his bits of food.. Instead, he fills himself full of soil and lets his tummy sort out the useful scraps. The rest of the dirt goes out through the tail end of his body and he leaves it on the ground in a curly little pile called a worm casting.

As the earthworm eats dirt to find food or to dig a burrow, he moves it bit by bit from place to place. He brings up deep, rich soil to the surface where the crops can use it. His tunnels loosen the dirt and make it crumbly. This lets in air and drains away soggy pockets of water. Mr. Pinky does all the useful things that the farmer does when he plows his fields.

One little earthworm cannot do very much plowing. But fifty thousand of them can move great piles of dirt. And there may be this many of them living in one acre of soil. Every day, all of them drag bits of old leaves and other decay down their burrows and bring up little piles of dirt from below. In a year, this army of earthworms can move around 15 tons of dirt. In 20 years, they can plow up a layer of dirt three inches deep.