Understanding Ultra-Fine Particle Lime
When buying any Lime product there are two critical factors that will determine its efficiency and cost effectiveness in raising the soil pH on your farm.
1. Purity. Fact - It’s the Calcium Carbonate portion of Lime that raises soil pH.
In New Zealand our Limestone quarries range in Calcium carbonate purity from approx 98% down toless than 50%.
To achieve a pH increase of say 0.2, as the Calcium carbonate purity decreases, the quality of lime required increases.
2. Particle size. Fact - It’s the surface area of exposed Calcium carbonate that determines Lime efficiency.
As Lime particle size is reduced its surface area increases exponentially.
Contrary to popular belief it is a scientifically proven fact that large particles of applied Limestone do not have any significant slow release effect in pastoral applications.
Understanding fine particle lime.
Consider grandad’s rule of thumb, “a ton to the acre”, if we place a 1 ton boulder of limestone in the middle of a 1 acre paddock we have ‘a ton to the acre’, however that won’t be very effective. If we crushed that same boulder down to Track Lime and spread it in the same paddock, you can guess how effective that’s going to be. Grind thatsame Limestone boulder down to Lime flour (far smaller that Ag-lime), and spread that, you know it will work. So now when it conmes to Lime you know the importance of particle size.
Very small particle sizes are measured in microns. There are 1,000 microns to a millimetre. A healthy human eye can only see as small as about 4 microns. Bacteria are around 1 to 2 micron. The smaller the micron number, the finer the particle size.
For agricultural use, Lime is sold under many generalised descriptions that are relative to the particle size of the product. As Lime particle size is such a critical factor, it’s important to have an understanding of these general descriptions.
Ultra-fine particle. An average particle size of less than 20 micron.
Lime flour. An average particle size of less than 50 micron.
Fine particle Lime. Crushed the usually sieved to 250 micron maximum particle size.
Crop-fine Lime. Similar to Fine particle Lime
Ag-Lime. Limestone crushed and sieved so that 95% is less that 2mm, (2000 micron).
Track Lime. Limestone crushed to 20mm, (20,000 micron).
Note: These descriptions and sizes may vary supplier to supplier, there fore it is important when buying Lime, to ask “What’s the particle size”? When buying Prilled, Granulated Limes or slurred products, ask “What was the particle size before it was Prilled or Granulated”?
When it comes to Lime the finer the particle size the and the higher the purity the better the results.
Andrew de Lautour ©