Lime: Not all it’s cracked up to be
Europe has placed a much greater emphasis on lime evaluation. Conference presenter Hans-Siegfried Grunwaldt, Ph.D., University of Applied Sciences, Faculty Agriculture, Kiel/Germany, described differentiation based on reactivity.
After extensive research in Europe, common lime sources are now broken up by source material, quality and reactivity, and must contain information that growers and retailers can use to determine how it will behave in soil.
If this isn’t enough to consider, particulate size (measured in mesh) also impacts reactivity, yet variations in state requirements for mesh size to determine a fineness factor are dramatic. Hoiberg pointed out that Iowa uses 4- and 8-mesh particle sizes in their calculation, and nine others also use 8-mesh as part of their fineness factor (though most include finer material also); yet a substantial body of research suggests that particles larger than 10- (and some suggest 20-mesh) have no pH changing value. Many states don’t include anything finer than 60-mesh in calculating the fineness factor. Research suggests that as the mesh size increases/particle size decreases, the speed and the level of pH change increases dramatically.
Gudrun Mahrt, Columbia River Carbonates, AGRO, described this range in reactivity, with particles passing a 100-mesh screen as having 100 percent reactivity in the soil within six months and particles between 20-mesh and 60-mesh reacting about 50 percent during the first year.
“What it may indicate is that in states that use coarser mesh fractions in determining the fineness factor, people have not been applying enough lime,” said Hoiberg. “Some of these coarse particles are not reacting in the soil, while the fines do. The rate of and completeness of reactivity in soil are poorly understood.”
Hoiberg suggested that as both are better understood application rates will likely be adjusted accordingly, as under German law. Grunwaldt reported that minimum particle sizes are defined by source and CaCO3 content. A 5-mesh chalk with 97 percent CaCO3 is allowed, while a hard limestone with only 70 percent CaCO3 requires a minimum 48-mesh to be considered reactive enough to perform as expected based on reactivity testing. While higher quality, finer particles may prove to have a premium value in many scenarios, there may be some situations where a slower reactivity will prove beneficial. Grunwaldt described just that with high reactive limes prescribed for heavy soils, large amounts of low reacting dolomites for sandy loam soils and slower reacting limes for sandy, organic soils and pastures. What all presenters agreed on at the meeting was that much additional research is needed.
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