Sunday, December 4, 2022

Alabama ag lime law amendment makes it easier to compare products

• By Steve M. Brown •

Gov. Kay Ivey signed Senate Bill 173, sponsored by Sen. Larry Stutts, into law in early May. The bill — assigned Act No. 2021-321 — requires agricultural limestone products to be labelled with their relative neutralizing value (RNV). This law will make it easier for farmers to compare agricultural limestone products based on quality.

What is relative neutralizing value?

Relative neutralizing value is a measurement used to determine quality of an agricultural limestone product. RNV is based on calcium carbonate equivalent (CCE, which is a measurement of the material’s ability to change pH) and particle size of the material.

Fineness of liming materials affects how quickly a lime will react with the soil. In Alabama, material which passes through a 60-mesh screen is considered 100% effective, and material that passes through a 10-mesh screen (but not a 60 mesh screen) is considered 50% effective. The formula for determining RNV is provided below:

• A = the percent of lime passing through a 10-mesh screen, but not a 60 mesh screen

• B = the percent of lime passing through a 60-mesh screen

Since the 1970s, Alabama’s lime law has specified that products cannot be marketed as an agricultural limestone unless:

1. The material has at least a 90% calcium carbonate equivalent

2. At least 90% of the material passes through a 10-mesh sieve

3. At least 50% of the material passes through a 60-mesh sieve

lime screens
Photo courtesy Alabama Cooperative Extension

Products that meet these requirements have an RNV of at least 63%. Therefore, producers can be guaranteed that a product is at least 63% effective if they buy an agricultural limestone product in Alabama.

However, there is no easy way to compare lime products without doing some extra math. The new amendment to the lime law will increase transparency by requiring companies to provide RNV on labels, making it easier for farmers and retailers to compare products.

Why is this change timely?

Precision agriculture technologies have allowed farmers to become increasingly precise with lime applications. Technology for variable-rate lime application often requires RNV to be entered into computer software to determine the appropriate amount of lime to apply (example, more lime is required for a product with 63% RNV compared to a product with 90% RNV).

Dr. Steve M. Brown is an Alabama Extension cotton agronomist. He may be reached at Auburn University.

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