Ask Big Jon

The Question of Lime

Q:  I have had some folks tell me that I should use gypsum instead of agricultural lime to raise soil pH.  Is that okay? 

A:  Use agricultural lime, not gypsum.  Agricultural lime (calcium carbonate) is quite different from gypsum (calcium sulfate).  From the food-plot planter's perspective, the biggest difference is that agricultural lime raises soil pH while gypsum does not.

Q:  Do you have to use as much pelletized lime as you would agricultural lime to raise soil pH the same amount? 

A:  Opinions vary on whether you must use the same amount of pelletized lime as it would take to equivalently raise soil pH with bulk agricultural lime, but the experts we have consulted suggest that one may use a weight of pelletized lime that is at least 70-75% of what the bulk lime recommendation would be and get the same effect.   

The key to understanding this is knowing that lime works to raise soil pH by particle-to-particle contact; a particle of lime must touch a particle of soil to neutralize it.  The “fineness” of lime is expressed in "screen size", which just means the fineness of the mesh the lime particles will pass through.  The finer the lime grains in a pound of lime, the more individual grains there are, and the more grains there are, the more dirt particles they will touch and neutralize (IF you work the lime into the soil properly and thoroughly).   

Remember that the pellets in pelletized lime are not all lime.  They are much smaller lime particles rolled up into little clay balls so that they will go through a broadcast spreader.  The actual pieces of lime that are in the balls are actually of smaller screen size than the lime particles in granular bulk lime.  What that means is that there are more “pieces” of actual lime in pelletized lime than there are in an equivalent weight of the more coarsely-ground agricultural, or bulk lime.   

That brings me to a tip about using pelletized lime that you are planning to disk in.  Remember that I said the pellet consists of lots of little lime particles rolled up into clay balls?  Try taking one of the pellets and leaving it on your driveway overnight.  Overnight, the ball will break down, and in the morning you will find a little pile of powdered lime where you left the pellet.  In the same way, it is a great idea to broadcast pelletized lime one afternoon, but wait until the next morning to disk it in.  That way, you are disking in the separate lime particles, not the whole pellet, and with vigorous "stirring" with your disk, you will get better  particle-to-particle contact.   

The key to raising soil pH with either bulk or pelletized lime is to work it into the soil thoroughly.  As I often heard the  former Director of Plant Breeding for the Institute, Dr. Johnson, say, “Lime pretty much stays where you put it.  You HAVE to disk it in thoroughly if you are going to raise soil pH.”  So, when you disk in your lime don’t just make one pass.  Instead, think about making pancakes: if you put pancake mix in a bowl and then the water, and make only pass around the bowl with the spoon, most of the water will not reach the mix.  However, if you stir vigorously and in multiple directions, the mix will be much better.  Same thing with lime—the better you disk in (multiple passes in different directions), the more particle-to-particle contact you will achieve with the soil. 

Another good tip is to disk the lime into the soil only within the first six inches (or even less if you are planting a relatively shallow-rooted plant like Imperial Whitetail Clover) and then disk the last ton in only in the top three inches or so.   When preparing to plant Whitetail Institute forages, it is not necessary to disk in your lime any deeper than that. If you do, you will be decreasing the effectiveness of the lime by mixing it with more dirt than you have to.  

Personally, when I want to lime a new plot site, I start six months before I intend to plant and disk in the amount of bulk lime required by my soil test.  Then, I add 800 – 1,000 pounds of pelletized lime right on top of the soil when I plant.  By doing it this way, I get the top four to six inches of soil up to proper pH by the time I plant, and the additional pelletized lime on top gives an extra pH kick to the surface of the soil where the seed will be germinating.  Then each year, I top-dress the plot with 800-1000 pounds of pelletized lime just to maintain soil pH at the surface to slow the descent of the soil into acidity. 

An article discussing pelletized and agricultural lime is available on-line at the following web page: http://www.whitetailinstitute.com/info/news/nov05/11.html.