Lime: Not all it’s cracked up to be
If you think lime is boring, think again. Although lime has long been shown to affect soil productivity, a recent meeting involving key members of the U.S. Department of Agriculture, academia and lime industry identified serious questions, concerns and significant opportunities related to liming material evaluation.
Adding annual pH testing and more predictable lime applications based on how these materials react in soil may boost soil health and productivity, which could mean more sales of product and services for full-service ag retailers and agronomists. However, better liming may reduce the need for applied nutrients. Of course, from a grower, environmental and regulatory relief standpoint, that is good news. Taken as a whole, the discussion raises the question, “Do we fully understand how liming materials are reacting in the soil and exactly how they are impacting soil health and associated processes?”
“We’ve got target pH for maximum yields figured out,” said Andrew Hoiberg, Ph.D., director of research and development, Calcium Products. “We brought USDA and Iowa State University researchers together with the lime industry to lay out inconsistencies that exist in how materials are evaluated and what that could mean for agriculture moving forward.”
Those inconsistencies start with state lime laws that follow 39 different ways to grade lime and 19 ways to define it. At the same time, there are inconsistencies simply with putting together a liming recommendation. The process seems simple.
Test the soil for pH. Test the lime for calcium carbonate (CaCO3) equivalent. Apply enough lime to equal the recommended rate of 100 percent calcium carbonate equivalent (CCE) needed to raise the pH to the desired level.
Unfortunately, once you get past the soil test and prescribing a target pH, the process starts to fall apart. Rather, it doesn’t always fall into solution, soil solution that is. It turns out that not only is reactivity (rate at which the lime dissolves in soil solution) for different types of lime poorly understood, reactivity based on particle size raises further questions.
“The CCE test is very accurate at describing the potential a liming material has to effect pH change, but it uses hydrochloric acid, a very strong acid that may not reflect the actual capacity of a material to react in weaker soil solutions,” explained Hoiberg.
VARIANCES IN LIME’S REACTIVITY
Dan Olk, Ph.D., research soil scientist, USDA-ARS National Laboratory for Agriculture and the Environment, pointed out that past research has shown calcitic limestone to be relatively more reactive and raises pH more quickly compared to dolomitic limestone. However, the established HCl test for determining CCE gives additional neutralizing power to dolomitic materials despite these fi ndings. Dolomitic limestone works fine as a liming material provided it is processed properly, and it is desired for soils deficient in magnesium.
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