Buyer Beware of Free Lime

The saying "there’s no such thing as a free lunch" comes to mind when talking about free lime. Over the last couple of months, I've received a few phone calls and heard conversations from farmers who have been using lime from an industrial plant as a free byproduct. However, before you load the spreader and cover your fields, it's worth asking: What's actually in that product, and how effective is it as lime?

In Pennsylvania, agricultural lime is regulated under the Pennsylvania Fertilizer, Soil Conditioner, and Plant Growth Substance Law. This law requires that any lime sold or distributed for agricultural use be registered with the Pennsylvania Department of Agriculture. Certified products must undergo laboratory testing for fineness (sieve analysis), calcium carbonate equivalency (CCE), and the detection of potential contaminants. Heavy metals are also tested to ensure the material is safe for crop production and will not cause long-term issues in the food chain. Only products that meet these standards can legally be sold or distributed as agricultural lime in the state.

That's why testing is so necessary when dealing with byproducts or "free" lime sources. Earlier this year, a sample of one such byproduct was analyzed, and the results showed that it would take nearly twice the application rate—and twice the tractor time—to deliver the same neutralizing power as certified ag lime.

If you're considering using one of these byproducts, your first step should be to test its liming capacity. Laboratories such as A&L Great Lakes in Fort Wayne, Indiana, or Spectrum Analytic in Washington Court House, Ohio, can provide this analysis. For help interpreting the results and applying them to your farm, you can reach out to your local agronomy educator.

The second step is to check for contaminants. For this, the Penn State Agricultural Analytical Services Lab offers a biosolids testing package. You will need to contact the lab to test for heavy metals under the EPA 503 guidelines test. For testing, you'll need to collect a cup of the material, complete the biosolids submission form, and send the sample in for analysis. This will provide a clear picture of any heavy metals or other unwanted compounds present in the material. When interpreting the finalized report back from Penn State AASL, follow the limit of quantification and the last page of the report titled "Appendix: Interpretive Guidelines for Use of Biosolids on Cropland." If all the thresholds are within the acceptable range on the last page, then your product can be applied to cropland. However, if it exceeds the threshold of acceptability, it would be worthwhile to consider finding an alternative product.

Potential Problems with Heavy Metals in Crops that are Fed to Livestock:

A primary concern here is contamination by toxic heavy metals, including arsenic (As), cadmium (Cd), mercury (Hg), chromium (Cr), and lead (Pb). Each of these elements can accumulate in an animal's body and interfere with various metabolic functions. Clinical signs depend upon the toxifying element, but most often the gastrointestinal tract, liver, and kidneys are affected. Signs may begin with very subtle changes in animal performance. Diagnosis is based on finding elevated concentrations of these heavy metals in the blood, liver, or kidneys.

Another challenging issue is the potential for the lime product to be contaminated with molybdenum (Mo). This element is a required nutrient; however, in ruminant animals, it can interfere with dietary copper availability, inducing a secondary copper deficiency condition. This is a unique situation in ruminant animals, as molybdenum interacts with sulfur within the rumen environment to form thiomolybdate compounds. Thiomolybdates will bind to copper in the rumen, preventing the copper from being absorbed by the animal. The production of thiomolybdates is influenced by the presence of sulfur in the diet or water sources. The sulfur (S) content of a potential lime source should also be evaluated, as it may directly contribute to copper deficiency. Copper (Cu) deficiency will present with different clinical signs depending on which biological function of copper is affected. Most often, one will notice changes in hair pigmentation, transitioning from a dark to a lighter color, due to impaired pigment formation. Subclinical copper deficiency may present as reproductive failure in females as well as impaired offspring health and productivity. Copper status is best evaluated via liver copper concentration; however, multiple blood samples from a potentially affected group can provide some indication.

In summary, free lime may look attractive, but without testing, you cannot know whether you're saving money or creating problems. The Pennsylvania Lime Law exists for a reason—to protect soil, crops, and food safety. Take advantage of certified lime whenever possible. If you want to experiment with byproducts, test them before spreading. Only use a product once you've completed your homework on it. If you haven't, unintended consequences could loom on the horizon with heavy metals accumulating in your livestock.