Lime is not just lime. There are differences.

The number one thing you can do to help boost yields, improve weed control, improve nitrogen use efficiency, and improve soil health isn’t solved by a biological product, foliar feed, cover crop, planter attachment, or new, flashy technology. The answer is so simple, we don’t even talk about it anymore and it is two little letters representing two words that few know – pH.  pH stands for “potential of hydrogen” or “power of hydrogen” and is a measurement of acidity or alkalinity. The pH scale runs from one to 14 with seven being neutral. Below seven is acid, above seven is basic or alkaline.

Over the last 10 years, we have been graphing our year-end soil test results to see what percentage of our macro soil elements are low or below the optimum range. What we have learned has now become predictable here in southern Illinois. On average, about 40 percent of the soil samples we take every year have a pH(w) (water pH) of less than 6.2. We have seen this number be as low as 30 percent and as high as 42 percent. What is even more shocking is that on average 12-15 percent are below a pH of 5.8 and 6-10 percent are below a pH of 5.4. It is almost as common to see a pH of 4.8, 4.9, or 5.0 as it is to see a pH of 7.5. So, we could draw the conclusion that pH could be THE yield limiting factor on about 40 percent of our farmed acres.

In corn, soybean, and wheat production, we desire our soil pH to be between six and seven with the “ideal range” being 6.2 and 6.8. This is the pH range where everything is firing on all cylinders in the soil. Our soil microbes and soil applied herbicides are happy, and roots can be better at taking up nutrients and water. When within the ideal pH range, we are also getting the maximum uptake and use of applied fertilizer. At a soil pH of 6.0, 20 percent of the fertilizer that we apply could be tied up in the soil or not taken up by the plant. At a pH of 5.5, that percentage of fertilizer climbs to 33 percent. We also can have potential yield loss because of what was mentioned above. Weed control, nitrogen use efficiency, water uptake, as well as plant and soil health can suffer.

I made a spreadsheet where we can put in the cost and yield goals of producing an acre of corn or beans to see what the potential dollar per acre loss could result from having a pH outside of the ideal range. In some instances, it becomes very costly NOT to correct your pH.

Provided by Kelly Robertson, Precision Crop Services LLC

The only way to correct soil pH is with limestone.

A lime product must contain carbonate (CO₃), such as Calcium Carbonate (CaCO₃) or Magnesium Carbonate (MgCO₃). Gypsum is not a lime because it contains no CO₃, only Ca (Gypsum is CaSO₄).Using gypsum to try to correct soil pH will lead to other problems. Anyone who advised you to use gypsum to alter soil pH is misguided and does not understand the neutralizing power of the carbonate component of limestone. I will say it again:  Gypsum is not a lime and will NOT change your soil pH.

Often when you take soil samples from the laboratory, they will generate a limestone recommendation based on the crops to be grown. Unless you specify what limestone you will use, these recommendations are made based on a pure limestone (100 percent) or what is called a “lime 90”, or 90 percent limestone. The problem with these recommendations is that we don’t buy 100 percent or 90 percent limestone; therefore, we or your agronomist must correct this number to the limestone being used.

In Illinois, we have a booklet that is published every year called the Illinois Voluntary Limestone Producers Handbook. This book consists of a compiled list of all participating quarries and the samples they submit show correction factor compared to a reference limestone. In this book, you can see the differences in one limestone vs the other and then compare their correction factors (CF). The correction factor is used to compare the lime in question to the pure lime or 90 percent lime. The higher the number, the more lime you will need to apply vs the smaller the number.

Let’s look at an example. 

Below, the lab recommendation shows we need 2 tons per acre of lime.

However, looking at the two limestone sources close to us we see that Lime 1 has a correction factor (CF) of 1.29. This means that we need to put on about 29 percent more of this lime to equal pure limestone or lime 90.

Looking at Lime 2 it has a correction factor of .74. Meaning we need about 25 percent less lime than a pure lime or lime 90.

Provided by Kelly Robertson, Precision Crop Services LLC

How is this possible?

Well, it goes back to fineness of the lime grind. The finer the grind, the faster it will break down and correct pH. You can see in the picture below the huge difference between these two lime products: Lime 2 is almost like a powder and Lime 1 has chips or almost rocks in it.

Provided by Kelly Robertson, Precision Crop Services, LLC

So, we need to compare the cost of the lime, the cost of trucking the tons and the spreading cost of those tons to get a true picture of which lime is the better buy. Just because it may be cheaper, doesn’t mean it will be the better buy. 

Provided by Kelly Robertson, Precision Crop Services LLC

In this case, even though Lime 2 costs more per ton, we haul less and spread less. In our example, we save $872 on 40 acres or $22/ac over Lime 1! A ton of lime is not necessarily a ton of lime. Our experience is that in most cases, when we do not “true” the lime source to the recommendation, we under apply!

Fixing pH is the simplest, most cost effective and highest ROI activity we can do to increase yields, control weeds, increase fertilizer efficiency and increase soil and plant health. It pays to fix pH, and it pays to do it right. Do the homework and do the math.