You Can't Afford Not to Lime

ARDMORE, Okla. — Agricultural producers want to get all they can out of their fertilizer dollars, but if their soil pH is too low, they may be shortchanging themselves. To maximize nitrogen, phosphorus, potassium and other nutrients, pH must be at the proper levels.

According to Jim Johnson, a soils and crops specialist and the Noble Foundation, as pH decreases below 6.5, phosphorus becomes less available. On a relative scale, only about 30 percent as much phosphorus is available when pH is below 6.0 versus when pH is above 6.5. Nitrogen and potassium start becoming less available below pH 6.0. Both are about 30 percent less available at pH 5.5 and 70 percent less available at pH 5.0. As pH continues to fall below 5.0, nitrogen, phosphorus and potassium become so unavailable that they are of little use to a growing plant.

"It is not uncommon for soil specialists at the Noble Foundation to see pH soil test levels below 5," Johnson said. "Commonly when the pH is in the 4s, other nutrient levels will be high. This is because the nutrients are not available to be taken up by the plants, so they build up in the soil."

The most effective way to raise pH is to apply a good-quality agricultural lime. The two factors that determine quality of lime are the calcium and/or magnesium carbonate content of the liming material and how finely the lime is ground. Often, local rock pits sell a product as ag lime that has good carbonate content but is not ground very fine. This makes the lime less effective. The more finely ground the lime, the faster it will raise the pH of the soil.

Incorporating lime into the soil makes it react faster than if it is surface applied. Therefore, applying lime before plowing to establish a new crop is a good idea. However, applying lime whenever it is possible is better than not applying lime at all. If lime is needed, the sooner it is applied the better, since lime can take several months to react and raise pH.

"The only way to know if and how much lime is needed is with a soil test. In addition to pH, a buffer index will be reported," Johnson said. "This tells a soil specialist how much lime to recommend based on your soil type."

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The Samuel Roberts Noble Foundation, headquartered in Ardmore, Okla., is a non-profit organization conducting agricultural, forage improvement, and plant biology research; providing grants to numerous non-profit charitable, educational and health organizations; and assisting farmers and ranchers through educational and consultative agricultural programs.

To learn more, visit the Noble Foundation Web site at http://www.noble.org.

More news releases available at www.noble.org/Press_Release