When is the last time your pasture has had a soil test? If it has been more than 3 years, you might want to consider making the investment. A soil test will show the pH of the soil, which is measure from a 1-14 scale. Anything under 7 is considered acidic and anything above 7 is considered alkaline; 7 is considered neutral. Having a pH between 6.0 – 6.8 is an ideal range for most forages as it allows nutrients in the soil to move efficiently to the grass or legumes to out compete with other weeds.
Before spreading lime, it is highly recommended to take a soil test. A miscalculation of the amount of lime needed could be unnecessarily costly.
The transition to cool, fall weather is the perfect time to make a lime application, because lime may take several months to break down. When applied in the fall, the rain and snow fall throughout the winter will help break down the lime, along with the freeze and thaw cycle.
If you look at the recommendations of your soil sample, it will tell you the amount of lime you need to apply to reach your buffer pH, but does it matter what type of lime you choose? It sure does.
Let’s take this hypothetical: You are making Kool-Aid, and you have the option to use sugar or artificial sweetener. Both look the same but will have a different impact. If you use 1 cup of pure sugar, it will probably taste great, but with a whole cup of artificial sweetener, you are going to have an interesting tasting experience.
This may be an extreme example, but it’s important to know that not all lime is the same. As you look at that soil test, it will say something like “Lime expressed in 100% pure CaCO3, adjust accordingly.”
How do we know how pure or strong our lime is? The answer is by the Effective Neutralizing Power (ENP) of the lime analysis. In other words, the power the lime has to push the pH up towards neutral 7.
Let’s take an example of a lime analysis that has 1,371 ENP. The first step would be to take: 1,371 ENP divided by 2,000 lbs./acre = 0.6855 or about 69%
This tells us that this lime will only be 68.55% effective, so now we must make another calculation. Let say that our soil sample says we need 1,700 pounds of lime to the acre.
1,700 pounds of lime divided by 0.6855 (%ENP) = 2,479.94 pounds of lime per acre.
So, in this case, even though our soil sample calls for 1,700 pounds of lime per acre, we need 2,479.94 pounds of that specific lime per acre due to the purity of the lime, 68.55%.
Let’s do another example, but this time we have a high purity lime. Our lime for this example is 2,293 ENP: 2,293 ENP divided by 2,000 pounds/acre = 1.1465 or about 114.65%
We will use the same recommendation as the last example of 1,700 pounds per acre: 1,700 pounds per acre divided by 1.1465 = 1,482.77 pounds of lime per acre.
If you compare the difference from the two examples (2,479.94 – 1,482.77), you are looking at just about a 1,000-pound difference in the amount of lime you would need. By knowing these calculations, we can make more informed decisions to improve our soil health and potentially save money at the same time.
