On 12 November 2013, members of the U.S. agricultural lime industry met near Iowa State University to discuss improving the measurement of limestone reactivity to better predict pH changes in soils. The goal of this conference was to compare current practices with other developed methodologies to determine if there are opportunities to improve measuring limestone reactivity in soils among a variety of liming materials. Research has shown that optimizing soil pH levels can help producers improve their yields while lowering environmental impacts in support of the Nutrient Management Strategy. In attendance were key leaders from the lime industry, academia and USDA.
According to conference presenters, current U.S. methods for testing liming material reactivity involve strong acids that may not reflect how they behave in soil environments. The methods are quick and repeatable, but the accuracy of these methods to describe a given material’s behavior in soil is unknown. It may be possible that the neutralizing capacity determined by these methods overestimates the actual reactivity of liming materials in the soil, which indicates the need for further investigation of improved methods. Further, current methods that don’t predict soil-based reactivity with accuracy are not compatible with advancements in precision ag technology.
“Research has shown that the most important factors when liming are your pH goal, material source, its particle size, and placement in the field,” said Dr. Andrew Hoiberg, Director of Research and Development at Calcium Products. “There’s a wide range of purity between various types of limestone and their ability to dissolve in the soil solution. We know that smaller particles react faster in the soil, but the overall reactivity is still very dependent on the source of the material.”
Dr. Dan Olk, Research Soil Scientist with the USDA-ARS National Laboratory for Agriculture and the Environment reported that the current U.S. lime methods only measure the potential reactivity. These methods appear unlikely to tell the grower the rate of reactivity of agricultural lime materials based on the chemical composition of the limestone, soil type and soil pH. By contrast, reactivity-based test methods could inform producers how quickly a specific lime source will actually react to increase soil pH. Successful implementation of such methods would allow growers to make better use of fertilizer inputs and reduce excess nutrients lost to the environment.