By Jeff Burbrink
Ag & Natural Resources Extension Educator, Purdue Extension LaGrange County

Jeff Burbrink

LAGRANGE — Over the past two weeks, I have talked to several people about applying lime to fields, pastures and lawns to solve various issues on their property. Many people do not understand the purpose of lime applications or the science behind when to apply it, and when not to apply it. It was just something they had heard that might work, or they had watched their parents or family do that.

Let me try to briefly explain why and when we should or should not apply lime (or sulfur) to our soils.

First, agricultural lime is nothing more than ground up limestone, or calcium carbonate. Indiana has some great sources of lime originating in our quarries to the south. Some of the lime is known as high calcium lime (or hi-cal). Some of our ag lime is called dolomitic lime, and it is somewhat higher in magnesium. Dolomitic lime is used when soils are low in magnesium.

Way back in the 1900s, some of the early research coming from the land grant colleges was showing crop yields could increase by adding lime to the fields. The results in those turn-of-the-century county corn club test plots were spectacular, and farmers started adding lime to fields without really understanding the science behind yields jump. In short, they thought of lime as a fertilizer.

The primary reason for the bump to crop yields was due to changing the pH of the soil so other nutrients were more available to the crops. Six or seven generations have passed since those demonstration plots got people excited about dramatic benefits of lime applications, and we are still trying to explain the “why” behind the science.

By the 1940s, it was understood the real value of adding ag lime to soils in Indiana occurred when the soil pH is low (acid soils). Our common field crops and our turf thrive best at a soil pH of 6.0 to 6.8 on mineral soils. When the pH is lower than 6 (acidic), the plants cannot find some of the key nutrients they need to thrive. That’s when we add lime.

If lime is applied to mineral soils that have a high pH, say above 7.0 (basic soils), it can have a detrimental effect, because again, some plant nutrients are not as available at pHs of 7.0 or greater. Above 7.5, deficiencies like phosphorus, iron and manganese can show up in some circumstances. In fact, most of these high pH solids need sulfur, not lime, because they need to have the pH lowered to more acidic levels.

You cannot look at the soil or the crop and know how much lime or sulfur to add to bring the crop to the most favorable pH. The soil pH determination is done with a soil test. In most fields, its good to take a soil test every 2-3 years. So the practice of applying 1,000 pounds of lime per acre annually is not based on any real knowledge, it’s just a habit, maybe passed down from generation to generation.

In fact, here in northern Indiana, over the past 30 years, we have been seeing soil pHs changing, moving higher (less acidic) in many situations, because the sulfur we used to get from the steel mills to our west is no longer falling from the sky as acid rain as it did for so many years. Sulfur, of course, is both a plant nutrient, and a way to lower pH. Farmers are seeing crop yields affected by this changing level of sulfur and pH, and many are now managing for this.

Please note that applying lime or sulfur does not instantaneously change the soil pH. It takes more than six months for the real effects to maximize. And, applying lime or sulfur over the top of an existing perennial crop, like alfalfa or turfgrass only changes pH in the top inch or so of soil, not 10-12 inches down where a lot of the roots are. For perennial plants like pastures, alfalfa and turf, the pH adjustment is best done six months before seeding.

The bottom line is: there are real scientifically valid reasons to apply lime and sulfur to lawns and fields, and that should be done with a soil test in hand. Spreading lime or sulfur because “it looks bad” or because “it is the way we always have done it” is not taking good care of your plants or soil.

I cannot cover this topic thoroughly enough in a simple newspaper article, so for further explanation, so I suggest reading canr.msu.edu/resources/facts_about_soil_acidity_and_lime_e1566 for field crops
and turf.purdue.edu/extpub/soil-testing-for-lawns/.