MISSISSIPPI STATE -- Fall applications of lime make the most sense for state producers, but experts suggest a soil test before applying it.

Larry Oldham, soil specialist with the Mississippi State University Extension Service, said controlling soil acidity is the most important aspect of soil fertility management. Adding lime changes the pH of the soil.

"If you've only got so much money to spend on a soil fertilizer input, invest in lime before you invest in mineral fertilizers such as phosphorus or potassium," Oldham said. "If you get your lime correct, the nutrients that are already in the soil will be more readily available. Nutrient availability is affected by the pH of the soil."

Lime requires water to react with the soil, so lime applied in the fall can take advantage of winter rains. This timing also allows it to be incorporated into the soil during fall tillage. Before adding lime or other nutrients, have the soil tested. Soils have different abilities to interact with lime; in addition to information on phosphorus, nitrogen and potassium, the test will come back with a pH and lime recommendation.

"If you have not had a soil test done in more than 2 years, have your soil tested as soon as possible," Oldham said. "Soils must be tested periodically because of weather and land use."

Over time, high levels of rainfall and heavy crop production pulls nutrients from the soil. Oldham recommended producers test soil at least every three years to determine nutrient needs.

How a soil sample is taken depends on the size and topography of the field and whether or not fertilizer has been applied.

"Fields with less than 20 acres can be sampled as one unit, unless there is a topography difference within the field, such as bottomland and an adjacent slope," Oldham said. "Any field larger than 20 acres should have more than one sample."

Take two samples from fields that have received surface-applied fertilizers over several years. Take the first sample from the regular 0- to 6-inch depth, and the other sample from the first 2 inches. Follow the soil test recommendations from the deeper sample to determine phosphorus and potassium management, and the results of the more shallow sample for lime management.

Soil samples cost $6 each at MSU's Soil Testing Laboratory. Oldham said their expense is well worth the benefit gained from knowing the nutritional requirements of a field.

There are still other considerations once lime needs have been determined. For example, the size of the lime particle affects how readily it reacts with the soil and how often it must be applied.

Art Smith, Extension area agronomic agent stationed in Tunica County, said growers in his area are well aware of the need for lime, but some don't test soil as often as they should.

"In some cases, the emphasis is not placed on soil testing until they start noticing a loss of productivity," Smith said.

He said most productive farming operations in his area are performing soil tests every two years and have gotten into a four-year liming rotation.

"With the economic conditions we operate under now, productivity is everything," Smith said. "Producers are addressing their liming needs better now than in the past."