Wednesday, 17 March 2021 11:56

Understanding agricultural limestone in North Carolina; basic information to protect consumers

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RALEIGH — Spring is in the air and many growers are already in the field preparing for the 2021 growing season. Similarly, gardeners are preparing beds either for planting vegetables or spring or summer landscape plants, which often includes applying lime to lower excessive soil acidity.


By applying lime according to soil test recommendations, you achieve an optimum pH for your soil and provide balanced availability of plant essential nutrients. It also enhances the chemistry of the soil for roots and important soil organisms to flourish.  

North Carolina is fortunate to have a lime law that is administered through the Plant Industry Division’s Seed and Fertilizer Section with the N.C. Department of Agriculture and Consumer Services. The N.C. Agricultural Liming Materials and Landplaster Act is to protect consumers so that products allowed for sale meet designated chemical purity and physical property or particle size requirements. The law also directs manufacturers of product specific minimum standards that must be met to be sold as lime in our state.

“While there is much complexity in this law as related to these requirements, the consumer can quickly determine if a product will be effective to neutralize acidity or increase soil pH by key information found on lime labels,” said Brian Bowers, seed and fertilizer administrator for the Plant Industry Division.

On the label of lime products, consumers should look for claims of the calcium carbonate equivalent as a percentage in weight, relative to pure calcium carbonate of 100 percent. This indicates that the product does have the chemical capability or purity to neutralize soil acidity. If it is not documented, then the product is not a lime and cannot be sold as such. 

There is no minimum calcium carbonate equivalent requirement for limestone sold in North Carolina. However, the product must be labeled to show the amount necessary to equal that provided by a liming material having a 90 percent calcium carbonate equivalent.  

The other important criteria consumers should look for relates to the physical aspect of lime or the size of limestone particles. In the crushing and preparation of limestone, screens with specific size openings are used to size particles. Smaller particles have greater surface area, which enhances chemical reactivity. In other words, a smaller particle of lime will dissolve much faster as it encounters soil acidity as compared to a larger particle. In North Carolina, 90 percent of particles are required to pass through a very small meshed screen (20 mesh screen - 0.85 millimeter opening) to be effective. If specific screen sizes are not listed on the product label, the material being sold is not a lime.

By looking at the label and using these tips, a discerning consumer is less likely to be misled into buying a product that is not effective as a lime. More information about lime products can be found at https://content.ces.ncsu.edu/soil-acidity-and-liming-basic-information-for-farmers-and-gardeners .