Many people with poor lawns get an urge in the spring to try to improve them. Before starting, it is a good idea to try to determine what caused the lawn to go bad and see if it can be corrected. Otherwise it may be a waste of effort.

The soil may be too acid. Most soils in the eastern part of the United States are too acid for good grwoth of lawn grasses. If you haven't applied lime to your lawn during the last five years, it probably is badly needed; lime will reduce soil acidity.

Another probable cause could be improper mowing. The green part of the grass blade produces the food of the plant. If too much of the grass is removed when it is cut, food production is reduced and root growth is seriously affected.

The way to find out if your soil is too acid is to have it tested. Residents of the District can have their soil tested free of charge by Cooperative Extension Service, University of the District of Columbia, 1331 H St. NW, which will provide instructions on how to take the samples and where to send them.

Residents of Virginia can have their soil tested at Virginia Polytechnic Institute, Blacksburg, Va. 24061, and residents of Maryland can have it done at University of Maryland, College Park, Md. 20742. Telophone your county extension agent for instructions.

If the soil is too acid or too alkaline, important nutrients become insoluble and unavailable for plant use.

The problem with lawnmowing is that it is difficult to get someone to do it who can be depended on to do it properly.

Bare spots in the lawn can be caused by oil and gas spills, female dogs, fertilizer burn, heavy foot traffic, damage from rock salt used for deicing the pavement and other kinds of soil contamination.

To repair bare spots it may be better to get a few strips of sod from a graden center, or take some sod from an out-of-the-way place in the lawn. Dig out some of the old soil, replace it with good top soil and cut the sod into appropriate sized pieces. Keep the sod watered for at least three weeks by which time it should be somewhat established.

It may be best to water it rather lightly every day because if it dries out before the roots catch on, the effort may be in vain. Don't let it dry out and odn't keep it soggy wet.

Watering too much too often will keep the soil soggy and cause death of grass roots. For good growth during hot weather, the grass needs about an inch of water once a week. It can survive underwatering but not overwatering.