New regulations that govern lime sales make it easier for producers to decide how best to meet their soils’ nutrient needs.

Mississippi’s lime law was established in 1993. In 1997, the regulations were amended to create a grading system, but these regulations were revised recently with input from the Extension Service, the Mississippi Agricultural and Forestry Experiment Station and other stakeholders. The new law went into effect Dec. 15.

“When the regulations were revisited, the concept of relative neutralizing value was included,” Larry Oldham, soil specialist with the Mississippi State University Extension Service, said. “This concept that measures the usability of lime has been part of Extension programming since 1997, but it was formalized into state regulations.”

Now when lime is purchased, the vendor must provide a relative neutralizing value, or RNV, of the product. Producers can take this value and comparison shop to find the best value for their specific crop needs.

Oldham said most lime used in Mississippi is either calcite or dolomite, both hard rock limes. These must be crushed into powder to be used. Lime reduces the acidity of soil to which it is added, and smaller particles raise the soil’s pH more rapidly than do larger particles.

Oldham said Mississippi producers need lime to produce their crops efficiently. About half the soil samples tested each year by the MSU Extension Service Soil Test Lab need lime. Most lime applications are made in the fall after harvest, but some producers add it in the spring.

Lime’s usefulness is based on how fine it is ground and how pure it is. Most lime used in the state is imported from other states, so transportation costs make lime costly for producers.” If the soil test comes back and tells a producer to add 2 tons of lime per acre and lime is $30 a ton, that’s a significant investment for that producer,” Oldham said. “The new regulations requiring vendors to state the relative neutralizing value of the lime give producers a way to compare input costs.”

Harry Ballard, branch director of feed, fertilizer, lime and plant amendment programs with the Mississippi Department of Agriculture and Commerce’s Bureau of Plant Industry, said the RNV percentage simplifies the information available about a particular lime product.

“The RNV takes the calcium carbonate equivalent and the two sieve measurements formerly used to determine lime grade and puts these into an equation,” Ballard said. “Using this equation gives you one number, the RNV, that you can use to compare limes. The law set a minimum RNV of 63 percent, and the higher the number, the better the lime.”

Bonnie Coblentz writes for Mississippi State University Ag Communications.