Delayna Sturgis, age 13, of Springfield, Ore., for her question:

PLEASE EXPLAIN HYDROPONICS.

Good soil has all of the foods within it that are necessary for plant growth. Almost all commercial agriculture ventures use the rich earth for planting, although a number of them are using a system called hydroponics. Hydroponics has also been suggested as a way to grow crops aboard ships at sea or in ice-covered Arctic areas where land isn't available.

Hydroponics is the science of growing crops without soil. Plants are grown in special tanks which are filled with sand, gravel or water. Nutrients in a special form, usually supplied to the plant through the soil, are then added to the water or sand.

Hydroponics is also called soilless agriculture, acquiculture, nutriculture and chemical culture. It was first tried in the mid-1800s and has been only used on a rather limited basis since. Commercial growers, for the most part, find hydroponics too limiting for their needs.

There are two types of hydroponics: water culture and gravel culture.

Using the water culture type of hydroponics, plants are actually suspended with their roots in tanks of water. Tanks are made of either plastic or metal, not wood.

Into the water goes a special brew of nutrients. A good mixture will include about 5 pounds 13 ounces of potassium nitrate, 1 pound of ammonium sulphate, 4 1/2 pounds of magnesium sulphate, 2 1/2 pounds of monocalcium phosphate and 5 pounds of calcium sulphate. This amount of nutrients will be added to 1,000 gallons of water. Once each month 1 ounce of manganous sulphate and about 5 drops of concentrated sulfuric acid will be added, and once a week 4 ounces of ferrous sulphate in 1 gallon of water will be put into the tank.

Air must regularly be pumped into the water culture hydroponics tank since the new roots will require lots of oxygen.

It is easier to grow plants using the gravel culture. A nutrient solution similar to that used in water culture is pumped through sand or gravel. Material not taken up by the roots drains back into a supply tank. Another method runs tiny tubes directly to each plant. The nutrient solution is then slowly dripped, and each plant receives a more direct feeding.  Plants grown without soil must receive a proper amount of artificial or natural light.

Scientists have not proven that hydroponics produce better crops than those grown in the soil. However, they can effectively study the needs of the plants. With hydroponics it is easy to vary the amount of nutrients the plants are receiving, and then scientists are able to determine the best ratio needed for proper growth.