Limestone is a cost-effective input, often yielding the highest ROI when correcting soil pH. Soil tests reveal that low pH is a prevalent issue, affecting around 40% of Illinois farmed acres.
By applying limestone to adjust soil pH, farmers can greatly improve crop yields, nutrient uptake, weed control and herbicide persistence, according to Kelly Robertson of Precision Crop Services.
The correct application rates and type of limestone used have the ability to bring growers a multiyear, cost-effective benefit.
"Compared to all the other inputs, limestone is very cheap. I can often get the biggest ROI from adjusting my soil pH," says Robertson, who participates in the Soy Envoy program, an initiative by Field Advisor and the Illinois Soybean Association (ISA).
When he is called upon to do problem-solving in Illinois fields, Robertson takes a soil test to help investigate the issue. About 90% of the time, one of the problems he identifies is the soil pH is low. In fact, the ISA estimates soil pH is possibly the No. 1 yield limiting factor on about 40% of the state's farmed acres.
"That means we've got low weed control or no weed control, as pH affects herbicide activity and how weeds die or don't die," Robertson explains. "It also affects persistence, how long that chemical will stay in the soil. It affects nutrient uptake. It also works with the microbial activity in the soil, and it also works with plants in regulating water uptake."
He offers farmers a couple of recommendations as they plan their fertilizer program for the 2025 season.
Do a soil test on a regular basis. "Especially as they pick up new (ground), farmers need to be soil testing on a regular basis to know what the pH of the soil is," he says.
Know that not all limestone is created equal. Soil pH levels need to be adjusted based on the specific limestone the grower plans to use.
"The recommendation you get (from the lab) is often for pure lime or a 90% limestone," Robertson says. "The problem in Illinois is we don't have those. Farmers often take the recommendation from a soil testing laboratory and use that by itself - without adjusting it to the limestone that they have available or that they could buy locally."
In some cases, the limestone farmers end up purchasing is not at a quality or purity level the laboratory recommends.
"So, even when we are applying limestone, in some cases we are underapplying what was really needed," Robertson says.
He encourages farmers to consult various resources to help establish the quality of the product they are selecting and determine the proper amount of lime that is needed to meet the laboratory's recommendations.
He says an excellent online resource for Illinois farmers is the Illinois Voluntary Limestone Program Producer Information booklet. "This is a yearly, updated list of the quarries in Illinois," he says, adding certified crop advisers, state soybean associations and soy envoys are other good resources.
