By Greg LaBarge, CCA, Ohio State University Extension
Depending on your location, you may have a few options for ag liming materials. There are several questions to consider in a lime purchase. What is the calcium or magnesium content? How easily does the product spread with available equipment? Can we address other soil and management goals with the lime source available? Another critical question is, what is the most cost-effective source?
Fortunately, the Ohio Department of Agriculture regulates products sold as agricultural lime in Ohio. A key part of the regulation is providing an analysis number that allows us to compare lime sources and make accurate applications.
The number that every lime product sold in Ohio must show on the labeling is the Effective Neutralizing Power or ENP. The ENP is a calculated value based on total neutralizing power (TNP), fineness of grind, and percent moisture.
ENP provides a convenient way to compare lime sources on a cost-per-acre basis. We can compare sources with three numbers: your lime recommendation, ENP, and the lime material cost delivered to the field. The calculation is Cost ($ /A) = ( Lime Recommendation / (ENP / 2000)) X (Material Cost in $/ton).
ENP is also helpful in adjusting the amount of liming material applied to reach the target pH your recommendation is based on. Our lime recommendations are in the Tri-State Fertilizer Recommendations, Bulletin 974, on page 15, Table 4. The lime amount in table 4 is based on a lime material with a 2000 ENP value. If the ENP for a lime source is higher than 2000, you will use less lime; if the value is less than 2000, you will use more lime to meet the target recommendation.
You can find a two-page guide on developing a lime recommendation plus evaluating different lime sources at https://go.osu.edu/limeworksheet.