Correcting acid soil conditions through the application of lime can have a significant impact on crop yields, especially alfalfa. Since seeding alfalfa is expensive and a stand is expected to last for several years, getting lime applied and acidity corrected before seeding is critical, says Jill Zimmerman, Kansas State University ag specialist.
"Liming is one of the most essential but often overlooked management decisions a producer can make," Zimmerman says.
She says a routine soil test will reveal the pH level of the soil, and this will determine whether lime is needed on the field. Target pHs can vary due to the pH of the subsoil.
Where the subsoil tends to be acidic, a higher target pH is used to ensure adequate pH conditions in the root zone and provide sufficient amounts of calcium and magnesium.
Most soils with a high-pH basic subsoils can provide additional calcium and magnesium to meet crop needs. Soils with more clay and organic matter will have more reserve acidity at a given pH and will require more effective calcium carbonate (ECC) to reach a target soil pH than will sandy soil," Zimmerman says. "This is why two soils may have the same soil pH, but quite different buffer pHs and different lime requirements."
Lime materials can vary widely in their neutralizing power, Zimmerman says. The two factors that influence neutralizing value and are used in determination of the ECC content are the chemical neutralizing value of the lime material relative to pure calcium carbonate and the fineness of crushing, or particle size, of the product. The surface area of the particles is critical for neutralizing to occur, she says.
"Expressing recommendations as pounds of ECC allows fine-tuning of rates for variation in lime sources and avoids under- or overapplying lime products," Zimmerman adds.
She says research has clearly shown that a pound of ECC from ag lime, pelletized lime, water treatment plant sludge, fluid lime or other sources is equal in neutralizing soil acidity. All lime sources have a very limited solubility and must be incorporated and given time to react with and neutralize the acidity in the soil.
"While most ag limes contain both calcium and magnesium, the relative concentrations of the two essential plant nutrients vary widely," Zimmerman says. "While the advantages and disadvantages of using a dolomitic, magnesium-containing lime versus a calcitic lime — low-magnesium, high-calcium lime — have been discussed for years, the differences are slight unless your soil is deficient in magnesium."
In Kansas, for example, she says both dolomitic lime and calcitic lime are suitable for use on cropland.
Under most circumstances, the cost per pound of ECC applied to your field should be a primary factor in source selection, Zimmerman says. Such factors as rate of reaction, uniformity of spreading and availability should be considered, but the final pH change and subsequent alfalfa growth will depend on the amount of ECC applied.
"With no-till, lower rates of lime have been shown to be cost-effective in many cases," she says. "This is because lime is relatively immobile and will react only with the top 2 or 3 inches of soil."
She adds that current Kansas State lime recommendations suggest that “traditional” rates should be reduced by 50% to 60% when surface-applied in no-till systems or when applied to existing grass or alfalfa stands.