MISSISSIPPI STATE -- Homeowners sprucing up their lawns for spring should be careful using fertilizers as two of the most common types may harm area water quality if managed poorly.

Dr. Larry Oldham, soil fertility specialist with the Mississippi State University Extension Service, said movement of nitrogen and phosphorus from soils to water supplies raises water quality concerns.

"Elevated nitrate in drinking water has possible negative health affects," Oldham said. "Excess phosphorus that gets into surface water can promote algae growth to where it chokes out more desirable plant and animal species."

Oldham said what is done to individual lawns and gardens may seem unimportant to the community, but the accumulated impact of what happens on a small scale can be significant.

"Each lawn and garden by itself is small, but decisions made by individual homeowners have important cumulative effects in maintaining and protecting the environment," Oldham said. "Simply following a few common sense practices will demonstrate your stewardship."

Among these practices are soil testing, proper fertilizer application rates and times and controlling fertilizer runoff.

Apply phosphorus and potassium based on soil test results and recommendations. When these nutrient levels are high, adding more does little to increase plant productivity.

Soil testing is less useful for nitrogen management, as this substance changes forms rapidly in the warm, humid Mississippi climate. However, Oldham said environmentally conscious recommendations for nitrogen are provided by MSU soil test reports.

Most fertilizer recommendations for homeowners refer to a 1,000-square foot area, or an area 20 feet by 50 feet. With nitrogen application, it is especially important to carefully follow these guidelines.

"Managing all fertilizers properly is crucial to minimizing potential water quality problems," Oldham said.

Some homeowners dispose of unused fertilizer by spreading excess on too small an area, a practice they should avoid, Oldham said.

"The soil has an enormous capacity to store or filter nutrients, but it is not infinite," Oldham said. "After many years of applying too much fertilizer, many lawn and garden soil samples have extremely high levels of phosphorus and potassium."

When applying fertilizer, fill applicators over a hard surface, and sweep up any spills. Over watering nitrogen-fertilized areas can wash the nutrient away from the roots, especially in sandy or coarse soil. Never wash fertilizer into street drainage, and control erosion to limit the amount of phosphorus that leaves the lawn with erosion. Remove plant debris from hard surfaces where rain could wash phosphorus from these into the water supply, and never overspread fertilizer into surface waters.